Protecting Water Quality: Best Management Practices for Row Crops Grown on Plastic Mulch in Virginia

Authors: Mary Leigh Wolfe, Department of Biological Systems Engineering; B. Blake Ross, Department of Biological Systems Engineering; J. Fred Diem, Virginia Cooperative Extension; Theo A. Dillaha, III, Department of Biological Systems Engineering; and Katherine A. Flahive, Department of Biological Systems Engineering

Publication Number 442-756, June 2002

This report was 100% ($25,000) funded by the Virginia Coastal Resources Management Program at the Department of Environmental Quality through Grant #NA50312-99-6-PT of the National Oceanic and Atmospheric Administration, Office of Ocean and Coastal Resource Management, under the Coastal Zone Management Act of 1972, as amended. The views expressed herein are those of the authors and do not necessarily reflect the views of NOAA or any of its subagencies.

This document was prepared to meet the requirements of section 6217 of the Coastal Zone Act Reauthorization Amendments of 1990 as administered by the Virginia Department of Conservation and Recreation.

Table of Contents

Chapter 1 Introduction

Chapter 2 Water Pollutants and Pollution Control Measures

Chapter 3 Practice Effectiveness and Implementation

Chapter 4 Guidelines for Developing Water Quality Protection Plans for Crops Grown on Plastic Mulch in Virginia

Chapter 5 Example Water Quality Protection Plans

Technical References

Appendix A Financial Programs

Appendix B Websites

Appendix C Contact Information

Acknowledgements

Technical Advisory Committee

Growers Advisory Committee

Return to Table of Contents

Chapter 1 Introduction

This handbook focuses on BMPs for row crops grown on plastic mulch. Such a production system includes plant rows, often bedded, covered with impervious plastic mulch alternated with uncovered, inter-row spaces. Usually, drip irrigation tubing is placed under the plastic mulch to provide water and nutrients to the crop. In some cases, overhead sprinkler irrigation is used. In a few instances, no irrigation is employed.

Row crop production with plastic mulch has been shown to increase profitability for most fruits and vegetables, such as tomatoes, strawberries, and peppers, compared to conventional row crop production (without plastic mulch). Increased profitability is due to increased yield and improved crop quality.

Production is often enhanced by earlier plant growth and maturity compared to production without plastic mulch. Some crops grown with plastic mulch can be harvested one to two weeks earlier, which often enhances marketability. Plastic mulch, by preventing contact with the soil, provides cleaner crops, decreases incidence and severity of disease, and reduces spoilage. Plastic mulch also discourages weed growth and retains soil moisture.

Because of the differences between crop production with plastic mulch and conventional crop production, requirements and conditions for water quality protection differ. For example, applying fertilizers directly under the plastic mulch, a common production practice, reduces the potential for nutrient losses; thus the need for additional nutrient control BMPs should be less for crop production with plastic mulch. Conversely, utilization of plastic mulch can substantially increase the amount of runoff from a field, thereby requiring implementation of additional runoff control BMPs.

Some BMPs that have been determined to be effective for conventional production may not be effective for crop production with plastic mulch, and, conversely, some practices that may not be appropriate for conventional production may be appropriate for crop production with plastic mulch. Because information about BMPs for crop production with plastic mulch is limited, this handbook was developed to assist producers and water quality specialists in selecting and implementing water quality protection practices for crop fields with plastic mulch.

Chapter 2 of the handbook begins with a description of the impacts of plastic mulch on runoff, as well as leaching. Because the extent of NPS pollution is closely tied to runoff, control approaches must consider the effects of land use activities on runoff. Chapter 2 also describes pollutants that are associated with crop production, including sediment, nutrients, and pesticides. Management practices to control NPS pollution resulting from crop production with plastic mulch are identified. Chapter 3 focuses on the effectiveness of individual practices and describes systems of management practices to protect water quality. Guidelines for developing water quality protection plans are presented in Chapter 4. Chapter 5 includes example water quality protection plans developed using information from the handbook.

Appendix A describes financial assistance programs related to BMP implementation. Appendix B includes a list of websites with information related to crops grown on plastic mulch. Appendix C lists contact information for Federal, state, and local agencies that provide educational information and technical assistance.

This handbook is a state-wide guide to BMPs for protecting water quality with respect to row crops grown on plastic mulch. The handbook does not address other plant production systems that utilize plastic mulch, such as nursery and greenhouse operations. This is not a production handbook; production guidelines and information are available from a number of sources, some of which are cited in the Technical References section following Chapter 5. Major information sources consulted during preparation of this handbook are also listed in the reference section.

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Chapter 2 Water Pollutants and Pollution Control Measures

Best management practice effectiveness depends upon site-specific conditions, such as soil, slope, crop, distance to receiving waters, and the specific pollutant being considered. The mechanisms that BMPs utilize can be grouped into the following general categories: increase infiltration, reduce runoff, reduce percolation, control erosion, enhance sedimentation, reduce chemical (nutrients and/or pesticides) inputs, and provide treatment. The following sections describe the hydrologic principles related to pollutant transport, the potential pollutants from crop production with plastic mulch, and management practices that address each pollutant.

2.1 Hydrology

Runoff
Runoff occurs when the rainfall rate, or irrigation application rate, exceeds the intake capacity of the soil and after the small surface depressions have been filled. The major factors that impact runoff are crop characteristics, terrain features, soil properties, and the frequency, intensity, and duration of rainfall events.

Fields with close-tilled crops usually have less runoff than those with widely spaced row crops. Steeper slopes result in greater runoff at higher velocity. Fine-textured soils such as clays have lower infiltration rates and, consequently, higher runoff volume than coarse-textured soils such as sands. The USDA-Natural Resources Conservation Service (NRCS) has defined hydrologic soil groups to classify soils in terms of runoff potential:

Group A: lowest runoff potential; deep sands with little silt and clay

Group B: moderately low runoff potential; sandy soils not as deep as group A

Group C: moderately high runoff potential; shallow soils with considerable clay and colloids, though less than group D

Group D: highest runoff potential; mostly clays of high swelling percent, and some shallow clays that are impermeable.

Table 2.1 lists some major Virginia soils that fall into each of the hydrologic soil groups.

Crop fields with plastic mulch in Virginia can have more than 50% of the cultivated portion (row and inter-row areas) of the field covered by impervious plastic film; percent coverage varies widely depending on the crop and cultural practices. As a result, these cropping systems can significantly increase runoff volume compared to conventional row crop production systems. The impact of plastic mulch on runoff amount is greater for soils with lower runoff potential. For example, for a given field and rainfall event, the relative increase in runoff (plastic mulch vs. conventional) will be greater for a group B soil than for a group D soil.

Figure 2.1 provides estimates of rainfall excess, or potential runoff, for both conventional and plastic mulch scenarios for two rainfall intensities. These maximum runoff amounts are based on soil properties (group C assumed) and cover characteristics (row crop with 0% and 30% coverage by plastic mulch assumed). As water flows over a given field, less infiltration will occur if part of the field is covered with plastic mulch. The portion of this potential runoff that leaves a field also depends on topography, including slope and flow patterns. Considering topographic effects, the actual runoff leaving a given field represents a greater proportion of the potential runoff when there is coverage by plastic mulch as opposed to zero coverage.

The impact of plastic mulch on runoff is particularly significant during smaller storms, i.e., storms that usually produce little or no runoff without plastic mulch (Figure 2.1). As storm intensity and duration increase, the percent difference between the amount of runoff from plastic mulch and conventional fields decreases due to saturation of the soil and reduced infiltration capacity.

In-field practices to reduce runoff from crop fields with plastic mulch are described in Table 2.2. Standards and guidelines for many practices are provided by a variety of sources, such as the Natural Resources Conservation Service. Applicable standards and/or guidelines that were in place at the time this handbook was printed are cited in Table 2.2 and subsequent tables that describe additional BMPs. Standards and guidelines are updated regularly; the most current information should always be used. The Virginia Conservation Practice Standards developed by NRCS in Virginia should be used when available.

Table 2.1 Selected Virginia soils characterized by hydrologic soil group (from county soil survey reports)

Physiographic Region	Soil Name	Hydrologic Soil Group
Coastal Plain	Bojac	B
	Chickahominy	D
	Dragston	C
	Emporia	C
	Kenansville	A
Piedmont	Munden	B
	Pamunkey	B
	Suffolk	B
	Tetotum	C
	Appling	B
	Bolling	C
	Bucks	B
	Cecil	B
	Chester	B
	Leaksville	D
Blue Ridge	Tatum	B
	Hayesville	C
	Myersville	B
	Porters	B
Ridge and Valley	Dekalb	C
	Frederick	B
	Groseclose	C
Cumberland Plateau	Pagebrook	D
	Berks	C
	Shelocta	B
	Grigsby	B

Percolation
Percolation is the process by which water (rainfall/irrigation that infiltrates the soil) moves downward through and below the root zone. Water that percolates through the root zone may transport dissolved chemicals, such as nutrients and pesticides. Depending on the depth to the water table, chemicals may reach ground water. In some Virginia cropland, ground water may be only a few feet below the soil surface, while in other areas, ground water may lie several hundred feet below the surface of the soil.

The rate at which drainage water percolates downward through the soil depends primarily on soil properties and may also be influenced by tillage and compaction. Preferential flow paths, such as cracks, old root channels, animal burrows, and sinkholes and large channels in the limestone of karst areas, may promote relatively rapid downward movement. The time in transit from the soil surface to ground water may range from only a few minutes to years.

Most crop production with plastic mulch in Virginia utilizes an irrigation system to provide water to the crop. Irrigation applications should be managed to reduce runoff and minimize percolation in order to protect ground water quality. In contrast to overhead sprinkler irrigation, drip irrigation under plastic mulch can result in less percolation and runoff because water is not applied to the inter-row areas. If irrigation is a necessary component of the crop production system, irrigation water management practices described in Table 2.3 will help minimize percolation and reduce runoff in crop fields with plastic mulch.

Table 2.2 In-field practices to reduce runoff from crop fields with plastic mulch

Practice	Features	Also Listed in Table(s):	Applicable Standards1 or Guidelines
Contour Farming	Tillage, planting, and other farming operations performed on or near the contour of the field slope Reduces runoff, erosion, and transport of sediment and other pollutants	2.5, 2.7, 2.8	NRCS-VA 330 NRCS 331
Deep Tillage	Tillage operations commonly referred to as deep plowing, subsoiling, or ripping Fractures restrictive soil layers thereby increasing infiltration in the inter-row area Most effective when repeated periodically	2.5, 2.8	NRCS 324
Inter-row Cover Crop	Established grasses, legumes, forbs, or other herbaceous plants in inter-row areas during the growing season Reduces runoff and erosion	2.5, 2.7	NRCS 340
Row Direction	Straight rows laid out across the dominant field slope Use when contour farming is not feasible Reduces runoff, erosion, and transport of sediment and other pollutants	2.5	--
Winter Cover Crop	Established grasses, legumes, forbs, or other herbaceous plants throughout the field for winter cover Reduces runoff and erosion, manages excess nutrients in the soil profile, and aids weed suppression	2.5, 2.7	NRCS 340
1NRCS refers to USDA-Natural Resources Conservation Service Conservation Practice Standard; and NRCS-VA refers to Virginia Conservation Practice Standards developed by NRCS in Virginia.

Table 2.3 Irrigation water management practices to minimize percolation and reduce runoff in crop fields with plastic mulch when irrigation is a component of the production system

Practice	Features	Also Listed in Table(s):	Applicable Standards1 or Guidelines
Drip Irrigation	Irrigation system for distribution of water under plastic mulch directly to the root zone Efficiently and uniformly applies irrigation water and chemicals, reduces leaching	2.5, 2.7	NRCS 441 ASAE EP405.1
Irrigation Scheduling	Water management strategies intended to apply the optimal amount of irrigation water only when needed by the crop Reduces leaching potential by maintaining optimal soil moisture levels Requires monitoring of soil moisture status, crop growth stage, and weather conditions	2.5, 2.7	CVPR
1NRCS refers to USDA-Natural Resources Conservation Service Conservation Practice Standard; ASAE refers to American Society of Agricultural Engineers Standards; and CVPR refers to Virginia Cooperative Extension Commercial Vegetable Production Recommendations.

2.2 Sediment

Four storm-dependent processes determine the amount and rate of erosion and sediment transport. These processes include (1) soil particle detachment by raindrop splash, (2) transport by raindrop splash, (3) detachment by runoff, and (4) transport by runoff. Raindrop splash is a major force in the detachment of soil particles from soil aggregates. The rate of detachment by raindrop splash is dependent upon raindrop size, distribution, and velocity. Soil detachment due to runoff is influenced primarily by the velocity of runoff over the land surface. While some soil particles are transported by raindrop splash, the major transport mechanism is runoff. Transport rate depends largely on runoff velocity and depth and soil particle size.

Some soils have great resistance to erosion while others are highly erodible. The soil erodibility factor indicates the susceptibility of a given soil to erosion by water. Values range from 0.05 to 0.69; higher values indicate greater susceptibility to erosion. Soil erodibility factors for some major Virginia soils are included in Table 2.4.

In addition to soil properties, soil erosion is ultimately the combined result of several other factors including rainfall amount and intensity, soil cover, and slope steepness and length. Of these factors, rainfall characteristics, some soil properties, and slope steepness are essentially uncontrollable. For example, soil properties such as the proportions of sand, silt, and clay cannot be altered economically. While it is not often feasible to change overall slope steepness, in some cases, it is possible to reduce slope slightly by land grading. Orienting rows/beds across the slope can reduce the slope in the direction of runoff.

Cover is the most significant factor in controlling runoff and soil erosion. A dense vegetative cover absorbs the energy of rainfall, decreases the amount and velocity of runoff, increases infiltration, and reduces sediment detachment and transport. Plastic mulch protects the soil surface from raindrop impact and erosion, and eliminates erosion in the area under the plastic mulch.

The remaining exposed soil, however, can have higher erosion losses due to increased runoff rates between the rows. If rows are relatively short, sediment loss from a field with plastic mulch may be less than from a similar field without plastic mulch. As slope length increases, however, runoff rates increase between the rows, providing more energy for erosion. Thus, for longer rows, sediment loss from fields with plastic mulch and bare inter-row areas will be higher than from conventionally cropped fields.

In general, for conventional crop fields, a relatively small number of large storm events over the course of a year account for the majority of annual soil erosion losses. For crop fields with plastic mulch, however, many more storms are involved in erosion losses annually because of the increased runoff potential.

Best management practices for soil erosion control include both cultural and structural measures. Cultural practices generally have relatively low initial cost unless new machinery is required. Such practices are effective in controlling erosion through protection of the soil surface from raindrop impact, by improving soil structure and infiltration rate, and by reducing runoff velocity. Cultural practices that can reduce soil erosion potential in crop fields with plastic mulch are listed in Table 2.5. Because techniques that reduce the quantity and velocity of runoff generally reduce erosion, practices listed in Table 2.2 for runoff control are also listed in Table 2.5.

Table 2.4 Soil erodibility factors for selected Virginia soils (K-factors from county soil survey reports)

Physiographic Region	Soil Name	Soil Erodibility (May vary based on texture)
Coastal Plain	Bojac	0.17
	Chickahominy	0.37
	Dragston	0.17
	Emporia	0.28
	Kenansville	0.15
	Munden	0.20
	Pamunkey	0.28
	Suffolk	0.28
Piedmont	Tetotum	0.28
	Appling	0.24
	Bolling	0.28
	Bucks	0.37
	Cecil	0.28
	Chester	0.32
	Leaksville	0.43
Blue Ridge	Tatum	0.24
	Hayesville	0.22
	Myersville	0.32
Ridge and Valley	Porters	0.17
	Dekalb	0.17
	Frederick	0.30
	Groseclose	0.43
Cumberland Plateau	Pagebrook	0.37
	Berks	0.17
	Shelocta	0.32
	Grigsby	0.28

Table 2.5 Cultural practices to minimize soil erosion in crop fields with plastic mulch

Practice	Features	Also Listed in Table(s):	Applicable Standards1 or Guidelines
Contour Farming	Described in Table 2.2	2.2, 2.5, 2.7 2.8	NRCS-VA 330 331
Deep Tillage	Described in Table 2.2	2.2	NRCS 324
Drip Irrigation	Described in Table 2.3	2.3, 2.7	NRCS 441 ASAE EP405.1
Inter-row Cover Crop	Described in Table 2.2	2.2, 2.7, 2.8	NRCS 340
Inter-row Mulching	Applying plant residues or other suitable materials not produced on the site to the soil surface Prevents crusting, reduces erosion, and controls weeds	2.7, 2.8	NRCS 484
Irrigation Scheduling	Described in Table 2.3	2.3, 2.7	CVPR
Row Direction	Described in Table 2.2	2.2, 2.7	--
Winter Cover Crop	Described in Table 2.2	2.2, 2.7, 2.8	NRCS 340
1NRCS refers to USDA-Natural Resources Conservation Service Conservation Practice Standard; NRCS-VA refers to Virginia Conservation Practice Standards developed by NRCS in Virginia; ASAE refers to American Society of Agricultural Engineers Standards; and CVPR refers to Virginia Cooperative Extension Commercial Vegetable Production Recommendations.

Table 2.6 Structural practices to control impacts of erosion from crop fields with plastic mulch

Practice	Features	Also Listed in Table(s):	Applicable Standards1 or Guidelines
Buffer Strips	Narrow strips of permanent, herbaceous cover established across the slope and alternated down the slope with wide cropped areas Reduces erosion and transport of sediment and other pollutants downslope	--	NRCS-VA 332
Constructed Wetland	Wetland that is constructed for the primary purpose of water quality improvement Treats surface runoff through biological, chemical, and physical processes Located between field and receiving waters Often prohibitive due to operational and space requirements	2.7, 2.8	NRCS 656 NEFH 650
Diversion	Channel constructed across the slope to intercept and divert runoff Use upslope of crop field to prevent runoff onto the field from upslope areas	2.7	NRCS-VA 362 (draft) VESCH 3.12
Field Border	Use downslope of crop field to direct runoff to desired areas Strip of permanent grasses established at the edges of a field (minimum 30 ft wide/60 ft wide at the downslope end of rows) Reduces erosion from border areas by protecting soil from machinery operations Traps sediment in runoff leaving crop fields at downslope end of rows Manages harmful insect populations by interrupting migration paths	2.7, 2.8	NRCS 386
Filter Strip	Strip or area of herbaceous vegetation situated between crop field (beyond field border described above) and receiving waterway Reduces sediment and adsorbed and dissolved pollutants in runoff Most effective when runoff is uniformly dispersed and not concentrated before entering the filter strip To prevent concentrated flow from entering the strip, use in conjunction with level spreader or other dispersion method	2.7, 2.8	NRCS-VA 393
Grassed Waterway	Natural drainageway within a field shaped and vegetated to convey concentrated runoff at a nonerosive velocity and prevent gully formation and erosion	--	NRCS 412
Level Spreader	Converts concentrated runoff to diffuse flow and releases it uniformly onto areas stabilized by vegetation Enhances effectiveness of filter strips and riparian buffers In applying the cited standard to fields with plastic mulch, the design event should be modified. The design should be for the 2-year, 24-hour duration event rather than the 10-year, 24-hour event.	--	VESCH 3.21
Precision Land Forming	Reshaping the land surface to improve drainage Reduces concentrated flow and erosion Soils must be of sufficient depth and suitable texture	--	NRCS 462
Riparian Herbaceous or Forest Buffer	Area of grasses, grasslike plants, and forbs (herbaceous) or trees and shrubs (forest) adjacent to and upslope from water bodies receiving runoff from fields Reduces sediment, nutrients, and pesticides in surface runoff and nutrients in shallow ground water flow Applied in areas adjacent to permanent or intermittent streams, lakes, ponds, wetlands and areas with ground water recharge that are capable of supporting woody vegetation (forest) or where the natural plant community is dominated by herbaceous vegetation	2.8	NRCS-VA 390 NRCS 391
Sediment Basin	Constructed to collect and store sediment and to detain runoff Prevents sedimentation in reservoirs, ditches, canals, waterways, and streams; prevents deposition on bottom Applies where physical conditions or land ownership preclude treatment of a sediment source by the installation of erosion-control measures to keep soil in place In applying the cited standards and guidelines to fields with plastic mulch, the modified design criteria provided below should be followed. Design capacity = normal permanent pool storage (if any) + runoff volume from 2-year, 24-hour design storm from the contributing area. The 2-year, 24-hour runoff amount should be estimated using the SCS/NRCS curve number runoff method. A weighted curve number should be calculated for the field, using a value of 98 for the portion covered by plastic mulch. Outlets for the detention structure may consist of a combination of principal and emergency spillways. The outlets must pass the peak runoff expected from the contributing drainage area for the design storm specified for the structure in the applicable standards or regulations. The principal spillway should provide at least a 60-hour drawdown time for the 2-year, 24-hour duration storm. Research has indicated that most of the pollutant reduction in detention facilities occurs within the first 60 hours of detention. Suggested procedures for determining the required maximum orifice diameter for the principal spillway riser are provided below. Use the modified version of the discharge equation for a vertical circular orifice. Q =    S         216,000 A =     Q         0.6 64.32h 1/2               2 d = 2 A 1/2        3.14 Q = volumetric flowrate through the orifice required to dewater the stormwater volume in 60 hours, ft3/s (Note: 216,000 = number of seconds in 60 hours) S = total stormwater volume for 2-year, 24-hour or larger storm determined using SCS/NRCS curve number method, ft3 A = orifice area, ft2 h = maximum head on the orifice, ft (distance from the horizontal centerline of the orifice to the crest of the principal spillway) d = orifice diameter, ft (should never be less than 3 inches to minimize clogging)	2.7, 2.8	NRCS-VA 350 NRCS 378
1NRCS refers to USDA-Natural Resources Conservation Service Conservation Practice Standard; NRCS-VA refers to Virginia Conservation Practice Standards developed by NRCS in Virginia; NEFH refers to the National Engineering Field Handbook (USDA-NRCS); and VESCH refers to Virginia Erosion and Sediment Control Handbook.

In contrast to cultural practices, structural measures usually have higher initial costs, but lower annual costs. They require proper design and construction and have a degree of permanency. Structural measures can be very effective in improving the quality of runoff and may allow more intensive crop production than would otherwise be possible. They are effective in controlling impacts of erosion primarily by reducing the amount of runoff and sediment delivered to receiving waters. Structural measures to control impacts of erosion are listed in Table 2.6.

2.3 Nutrients

Minimizing nutrient losses involves (1) limiting the availability of nutrients to be transported and (2) limiting the transport of available nutrients. Practices to limit the availability of nutrients focus on fertilizer application considerations, specifically amount, form, method, and timing. Practices to limit nutrient availability for transport from crop fields with plastic mulch are described in Table 2.7 and include most of the practices listed in Tables 2.2 and 2.3 for runoff control and irrigation water management, respectively, and in Tables 2.5 and 2.6 for erosion and sediment control.

The goal of nutrient management practices is to match nutrient applications to crop needs. Guidelines and specifications for soil testing and other aspects of nutrient management can be obtained from Virginia Cooperative Extension and the Virginia Department of Conservation and Recreation Nutrient Management Handbook. Fertilizer application rate recommendations for specific fruits and vegetables are available in the handbook, Virginia Commercial Vegetable Production Recommendations, which is updated annually.

For most crop fields with plastic mulch in Virginia, the pattern of fertilizer applications during the growing season is generally dependent upon the type of irrigation system in use. Applying fertilizers via irrigation provides nutrients as they are needed by the crop. Furthermore, drip irrigation applies both water and nutrients directly under the plastic mulch, which is particularly beneficial in limiting losses by percolation. When fertilizers are applied through an irrigation system, standards and guidelines for chemigation should be followed to avoid detrimental water quality impacts.

2.4 Pesticides

Pesticides can be lost in dissolved and adsorbed phases. The ratio of the amount of pesticide in the adsorbed and dissolved phases is termed the partition coefficient, which gives a good measure of pesticide leaching potential. If a pesticide is highly soluble, it will be primarily dissolved in water and very little will adsorb to soil particles. In general, herbicides are more soluble than fungicides and insecticides and, consequently, have a greater potential for leaching. More leaching occurs in coarse-textured soils with low adsorptive capacity and large soil pores that promote rapid water movement through the soil profile. Less leaching occurs in fine-textured soils with high adsorptive capacity and smaller pores for water movement.

Most pesticides rapidly degrade after application. Degradation is generally enhanced through interaction with soil. Some pesticides are persistent and do not degrade or have very slow degradation rates (long half-lives) and can build up in the soil over time with repeated applications. For example, in Virginia soils, there are low concentrations of legacy (banned) chemicals found even though they have not been available for decades. In addition, some currently used pesticides, such as copper compounds, do not decay and will accumulate in soils with repeated use.

Most pesticides are degradable and break down into daughter products and eventually inert compounds. The intermediate daughter products, however, can be more or less toxic than the original chemical. These transformations are dependent upon chemical properties, soil properties, and environmental conditions. The toxicity, half-life, and leaching potential of a pesticide must be considered in conjunction with its intended use and the fieldıs physical properties. The likelihood of a rainfall event shortly after a planned pesticide application should also be taken into account.

In crop fields with plastic mulch, pesticide residue due to overspray and wash-off is more likely to accumulate on the plastic mulch as opposed to the soil surface. Runoff carries the residue to the inter-row area and readily transports it from the field unless infiltration occurs. In most cases, infiltration-based practices should be more effective than erosion control practices in reducing pesticide losses.

Practices to control pesticide losses from crop fields with plastic mulch are identified in Table 2.8. Because techniques that reduce the quantity and velocity of runoff will reduce pesticide losses, practices listed in Table 2.2 for runoff control are also listed in Table 2.8. Although applying pesticides through drip irrigation allows better control than broadcasting or spraying, drip irrigation is not listed because few products are labeled for chemigation. In addition, drip irrigation cannot be used for foliar applications.

Integrated pest management (IPM) is the most cost-effective means of reducing pesticide losses in fields with plastic mulch. It is generally defined as a system of cultural, biological, and chemical pest management strategies that keep pest populations below levels that cause net economic loss while minimizing off-site environmental impacts. IPM programs can include strategies that range from conventional prophylactic use of pesticides to biologically-intensive methods that rely upon little or no chemical use. Successful IPM programs reduce off-site pesticide losses and impacts by reducing the quantities of pesticides used and by avoiding use of those with greater potential for off-site environmental impacts.

Four aspects of an IPM program are prevention, avoidance, monitoring, and suppression of pest populations. Prevention is the practice of keeping a pest population from infesting a crop or field. When a pest population exists, avoidance is practiced if the impact of the pest can be minimized through cultural practices. Monitoring and proper identification of pests through surveys or scouting programs should be performed as the basis for any suppression activities. Suppression of pest populations may become necessary to avoid economic loss if prevention and avoidance tactics are not successful. Tactics that address each aspect are presented in Table 2.9. The most appropriate tactics will vary from site to site, by pest and by crop.

An IPM program should be developed with a government or private consultant who has training and experience in developing and implementing such programs. Development and implementation of a program should include the following steps:

• identify the pest or pests and determine if control is warranted for each;
• determine pest control goal(s);
• know what control tactics are available;
• evaluate the benefits and risks of each tactic or combination of tactics;
• choose a strategy that will be most effective and will cause the least harm to the environment; and
• use each tactic in the strategy correctly.

Table 2.7 Practices to limit nutrient losses from crop fields with plastic mulch

Practice	Features	Also Listed in Table(s):	Applicable Standards1 or Guidelines
Chemigation	Application of chemicals through an irrigation system by mixing the chemicals with the irrigation water Proper chemigation safety measures are required to prevent backflow to the water source and chemical storage tank, undesirably high application rates, and spills	2.8	ASAE EP409.1 ASAE EP405.1 CVPR
Constructed Wetland	Described in Table 2.6	2.6, 2.8	NRCS 656 NEFH 650
Contour Farming	Described in Table 2.2	2.2, 2.5, 2.8	NRCS-VA 330 NRCS 331
Diversion	Described in Table 2.6	2.6, 2.8	NRCS-VA 362 (draft) VESCH 3.12
Drip Irrigation	Described in Table 2.3	2.3	ASAE EP405.1 NRCS 441
Field Border	Described in Table 2.6	2.6, 2.8	NRCS 386
Filter Strip	Described in Table 2.6	2.6, 2.8	NRCS-VA 393
Inter-row Cover Crop	Described in Table 2.2	2.2, 2.5, 2.8	NRCS 340
Inter-row Mulching	Described in Table 2.5	2.5, 2.8	NRCS 484
Irrigation Scheduling	Described in Table 2.3	2.3	CVPR
Level Spreader	Described in Table 2.6	2.6, 2.8	VESCH 3.21
Nutrient Management	Managing the form, source, amount, timing and method of application of nutrients to achieve realistic yield goals, while minimizing nutrient movement to surface and ground waters Base application rate upon soil and plant tissue tests and realistic yield goals Apply commercial fertilizers in efficient split applications Time nitrogen application to coincide with the period of maximum crop uptake Described in Table 2.6	--	NRCS-VA 590 NMH CVPR
Riparian Herbaceous or Forest Buffer	Described in Table 2.6	2.6, 2.8	NRCS-VA 390 NRCS 391
Row Direction	Described in Table 2.2	2.2, 2.5	--
Sediment Basin	Described in Table 2.6	2.6, 2.8	NRCS-VA 350 NRCS 378
Winter Cover Crop	Described in Table 2.2	2.2, 2.5, 2.8	NRCS 340
1NRCS refers to USDA-Natural Resources Conservation Service Conservation Practice Standard; NRCS-VA refers to Virginia Conservation Practice Standards developed by NRCS in Virginia; ASAE refers to American Society of Agricultural Engineers Standards; NMH refers to Department of Conservation and Recreation Nutrient Management Handbook; CVPR refers to Virginia Cooperative Extension Commercial Vegetable Production Recommendations; and VESCH refers to Virginia Erosion and Sediment Control Handbook.

When pesticides are used, it is essential that the most current information be obtained, in order to prevent environmental and health hazards. The Pest Management Guide for Horticultural and Forest Crops provides information for selecting pesticide application schemes for a particular crop. There are also special use labels for some pesticides on various commodities. Check with university or Extension sources for the latest labels. The handbook, Virginia Commercial Vegetable Production Recommendations, also provides information on the proper use of crop protectant chemicals. The Extoxnet database, available online at www.ace.orst.edu/info/extoxnet/ghindex.html, provides information regarding environmental hazards and other concerns related to chemical usage. Local Extension agents can provide assistance and answer questions related to these information sources.

Table 2.8 Practices to limit pesticide losses from crop fields with plastic mulch

Practice	Features	Also Listed in Table(s):	Applicable Standards1 or Guidelines
Chemigation	Described in Table 2.7	2.7	ASAE EP409.1 ASAE EP405.1 CVPR
Contour Farming	Described in Table 2.2	2.2, 2.5, 2.7	NRCS-VA 330 NRCS 331
Deep Tillage	Described in Table 2.2	2.2, 2.5	NRCS 324
Diversion	Described in Table 2.6	2.6, 2.7	NRCS 362 VESCH 3.12
Drip Irrigation	Described in Table 2.3	2.3, 2.5, 2.7	NRCS 441 ASAE EP405.1
Field Border	Described in Table 2.6	2.6, 2.7	NRCS 386
Filter Strip	Described in Table 2.6	2.6, 2.7	NRCS-VA 393
Integrated Pest Management	Managing agricultural pest infestations (including weeds, insects, and diseases) with a combination of cultural, biological, and chemical controls to reduce adverse effects on plant growth, crop production, and water quality Decreases use of pesticides, thus reduces pesticide losses from fields Four aspects are prevention, avoidance, monitoring, and suppression. Specific practices for each aspect are given in Table 2.9.	2.9	NRCS 595 CVPR PMG
Inter-row Cover Crop	Described in Table 2.2	2.2, 2.5, 2.7	NRCS 340
Inter-row Mulching	Described in Table 2.5	2.5, 2.7	NRCS 484
Irrigation Scheduling	Described in Table 2.3	2.3, 2.5, 2.7	CVPR
Level Spreader	Described in Table 2.6	2.6, 2.7	VESCH 3.21
Riparian Herbaceous or Forest Buffer	Described in Table 2.6	2.6, 2.7	NRCS-VA 390 NRCS 391
Row Direction	Described in Table 2.2	2.2, 2.5, 2.7	--
Sediment Basin	Described in Table 2.6	2.6, 2.7	NRCS-VA 350 NRCS 378
Spray Application Management	Managing the application of pesticides to achieve pest control, while minimizing pesticide movement to surface and ground waters Calibrate application equipment periodically Select correct sprayer tips Spray only during appropriate weather conditions	--	CVPR
Winter Cover Crop	Described in Table 2.2	2.2, 2.5, 2.7	NRCS 340
1NRCS refers to USDA-Natural Resources Conservation Service Conservation Practice Standard; NRCS-VA refers to Virginia Conservation Practice Standards developed by NRCS in Virginia; VESCH refers to Virginia Erosion and Sediment Control Handbook; NEFH refers to National Engineering Field Handbook (USDA-NRCS); CVPR refers to Virginia Cooperative Extension Commercial Vegetable Production Recommendations; ASAE refers to American Society of Agricultural Engineers Standards; and PMG refers to Pest Management Guide ­ Virginia.

Table 2.9 Tactics to address aspects of integrated pest management (IPM) programs to control pesticide loss from crop fields with plastic mulch (based on Coble, 2001)

IPM Aspect	Features
Prevention	Pest-free seeds and transplants Irrigation timing that avoids situations conducive to disease development Tillage and harvesting equipment cleaned between uses Field sanitation procedures Elimination of alternate hosts or sites for insect pests and disease organisms
Avoidance	Crop rotation such that the crop of choice is not a host for the pest Cultivars with genetic resistance to pests Trap crops Pheromone traps Cultivars with maturation dates that may allow harvest before pest populations develop Fertilization to promote rapid crop development No planting in areas of fields where pest populations are likely to cause crop failure
Monitoring	Insect traps Weather Soil Pest incidence and distribution for each field
Suppression	Cultural Management Optimized in-row plant populations Cover crops or mulches Crops with genetic resistance to pests in the rotation Physical Tactics Cultivation or mowing for weed control Temperature management or exclusion devices for insect and disease management Biological Control Mating disruption for pests Avoidance of pesticides or other practices that may reduce effectiveness of naturally occurring biological controls Baited or pheremone traps for certain insects Chemical Controls Cost:benefit ratio determination prior to use Pesticide selection based on least negative effects on environment and human health Site-specific suitability of pesticide based on environmental warnings on label Pesticide use limited to areas where pests actually exist or are anticipated Pesticide application device calibration prior to use and occasionally during the season Avoiding continuous use of chemicals with the same mode of action to prevent resistance development

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Chapter 3 Practice Effectiveness and Implementation

3.1 Practice Effectiveness

Practices in Figure 3.1 are grouped as "in-field" and "off-site" practices. The purpose of in-field practices is to reduce runoff, sediment, and associated pollutants below the levels that would leave a crop field without the practices. Off-site practices are intended to manage and/or treat runoff, sediment, and associated pollutants that leave a crop field. Successful implementation of in-field practices may reduce the size and extent of needed off-site practices.

Quantitative information on the effectiveness of practices in reducing pollution from fields with plastic mulch is not included in this handbook because limited studies have been conducted. In Virginia, one objective of a study conducted by Arnold et al. (2001) was to evaluate the movement of crop protectants from fields through various runoff control features. The specific features investigated included sediment basins, irrigation ponds, and forest buffers. The limited results of the study indicated that the sediment basins evaluated had the potential to improve the quality of runoff leaving fields with plastic mulch. The study indicated that irrigation ponds were not effective in removing pollutants from runoff. Forest buffers were effective in improving runoff quality. It was beyond the scope of the study to evaluate design criteria for sediment basins or to provide quantitative pollutant removal information for a variety of basins or forest buffers.

3.2 Management Practice Systems

Management practice systems should be designed with technical assistance from qualified water quality professionals. Each practice must be selected, designed, implemented, and maintained in accordance with site-specific considerations to ensure that the practices function together to achieve overall water quality goals. If, for example, IPM, cover crops, field borders, grass filters, and riparian buffers are used to address a pesticide problem in a field with plastic mulch, then pesticide applications need to be conducted in a manner consistent with grass filter and riparian requirements (e.g., sprayers must be turned off before entering field borders unless pests in the field border are targeted). In addition, runoff from the fields must be conveyed evenly to the field borders, which, in turn, must be capable of delivering the runoff to the filter strips and riparian buffers in accordance with design standards and specifications (shallow uniform flow).

Emergency measures used to quickly drain low areas in fields, such as shovel ditches, tend to concentrate field runoff and prevent the required even distribution of flow for buffer areas. If shovel ditches are used, they should be used in combination with other practices, such as level spreaders, that can redistribute the flow prior to discharge into filter strips or buffer areas. Alternatively, they can be used in combination with detention structures that can capture and treat concentrated flow. Under no circumstances should shovel ditches discharge readily to receiving waters.

Figure 3.1 Relative effectiveness¹ of practices in minimizing sediment, nutrient, and pesticide losses from crop fields with plastic mulch

Sediment
In-Field Practices	Off-Site Practices
Contour Farming Row Direction Inter-row Cover Crop Inter-row Mulching Winter Cover Crop Diversion (Upslope) Buffer Strips Irrigation Scheduling Drip Irrigation Precision Land Forming Grassed Waterway Deep Tillage	Sediment Basin Riparian Buffer with Level Spreader if needed Constructed Wetland Filter Strip with Level Spreader if needed Diversion (Downslope) with one or more of the above BMPs Field Border
Nutrients
In-Field Practices	Off-Site Practices
Nutrient Management Chemigation Irrigation Scheduling Drip Irrigation Winter Cover Crop Inter-row Mulching Inter-row Cover Crop Contour Farming Row Direction	Sediment Basin Riparian Buffer with Level Spreader if needed Constructed Wetland Filter Strip with Level Spreader if needed Diversion (Downslope) with one or more of the above BMPs Field Border
Pesticides
In-Field Practices	Off-Site Practices
Integrated Pest Management Spray Application Management Inter-row Cover Crop Contour Farming Row Direction Irrigation Scheduling Drip Irrigation Deep Tillage Winter Cover Crop Inter-row Mulching Chemigation	Riparian Buffer with Level Spreader if needed Filter Strip with Level Spreader if needed Sediment Basin (Downslope) with one or more of the above BMPs Field Border

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Chapter 4 Guidelines for Developing Water Quality Protection Plans for Crops Grown on Plastic Mulch in Virginia

Step 1. Collect data

1. Aerial photographs of the production fields and surrounding area
2. Locations of irrigation pipelines and hydrants, subsurface drainage networks, fencing, and other permanent infrastructure that may limit management options
3. Topographic map of the production fields and surrounding area U.S. Geological Survey topographic maps are available for all areas of the state. Maps can be purchased through the Charlottesville sales office of the Division of Mineral Resources of the Department of Mines, Minerals, and Energy (P.O. Box 3667, Charlottesville, VA 22903, 804-951-6340 (phone), 804-951-6365 (fax)) or from private companies, with some available through the internet. A more precise topographic survey of the production fields may be required if drainage patterns are not well defined in the production field area and for the design of detention facilities if they are needed. Such a detailed survey is often developed prior to designing the irrigation system as well.
4. Soil properties as found in county/city soil survey publications and/or available from NRCS
5. Locations of areas with vulnerable ground water (from soil or geologic maps)
6. Locations of any nearby waterbodies and environmentally sensitive areas, such as water supply sources, natural wetlands, and critical habitats The presence of environmentally sensitive areas in close proximity to a crop field may require more intensive measures to prevent pollutant discharge into the sensitive areas. There may also be buffer requirements or setbacks for certain activities near environmentally sensitive areas. Information on legal requirements, including water quality standards, can be obtained from local and state agencies, such as the Virginia Department of Environmental Quality (contact information is included in Appendix C). The Chesapeake Bay Local Assistance Department can provide information on the buffer policy in the locally designated Chesapeake Bay Preservation Area.
7. Locations and dimensions of any existing buffers
8. Information related to permit requirements

Step 2. Develop master site map

1. Location and boundaries of crop fields
2. Drainage patterns in the production fields for crops grown on plastic mulch
3. Downslope waterbodies and other environmentally sensitive areas that will receive runoff from the production fields
4. Drainage patterns (perennial and ephemeral drainageways) between the production fields and downslope waterbodies and other environmentally sensitive areas
5. Artificial drainage features such as ditches, surface water inlets, and subsurface drainage outlets
6. Areas with high runoff and erosion potential
7. Existing buffers

   Complete steps 3 through 7 for each field, considering the potential interaction between fields.

Step 3. Select in-field BMPs to reduce runoff and erosion from fields

Step 4. Select and design off-site BMPs

Step 5. Develop integrated pest management (IPM) program

Step 6. Develop nutrient management plan

Step 7. Develop irrigation/chemigation management plan

Step 8. Develop implementation schedule and maintenance plan

Step 9. Determine cost of practice implementation and operation

Step 10. Finalize plan

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Chapter 5 Example Water Quality Protection Plans

5.1 Example Water Quality Protection Plan ­ Eastern Shore

Step 1. Collect Data

Elevation of the farm ranges from approximately 15 to 35 ft. Slopes of the production fields are slight, ranging from about 1% to 3%. The production fields are located on Bojac sandy loam and loamy sand soils, while the riparian areas are located on Nimmo sandy loam. The following detailed descriptions of the principal soils at the site were obtained from the county soil survey.

• BOJAC LOAMY SAND, 2 TO 6 PERCENT SLOPES - Bojac loamy sand is gently sloping, very deep, and well drained. Erosion hazard is moderate for water and severe for wind. Cultivated crops and nursery stock are moderately well suited to this soil. This soil will contribute to the leaching of fertilizer below the root zone unless intensive nutrient management is applied. Hydrologic soil group B. Soil erodibility factor = 0.17. Depth to water table is approximately 4 to 6 ft.
• BOJAC SANDY LOAM, 0 TO 2 PERCENT SLOPES - Bojac sandy loam is nearly level, very deep, and well drained. Erosion hazard is slight for water and moderate for wind. This soil is prime farmland. It has few limitations for commercial use. Cultivated crops, nursery stock, pasture grasses, and legumes are well suited to this soil. This soil will contribute to leaching fertilizers below the root zone unless intensive nutrient management is applied. Hydrologic soil group B. Soil erodibility factor = 0.24. Depth to water table is approximately 4 to 6 ft.
• NIMMO SANDY LOAM, 0 TO 2 PERCENT SLOPES - Nimmo sandy loam is a nearly level, very deep, and poorly drained soil that is located on flats and in depressions of Carolina Bays. Erosion hazard is slight for water and moderate for wind. This soil has severe limitations for agricultural and commercial use. Cultivated crops and nursery stock are moderately suited to drained areas. Pasture grasses, legumes, and timber are more suited to this soil. This soil may contribute to fertilizer leaching below the root zone. Hydrologic soil group D. Soil erodibility factor = 0.20. Depth to water table is approximately 0 to 1 ft.

Environmentally sensitive areas adjacent to the production fields include North and South Creeks and the marshes and estuary to the east. There is also a drainage ditch parallel to the county road to the west that will transport any entering runoff directly to North and South Creeks. The two large constructed ponds, one on North Creek and the other at the southeast corner of the farm, drain a portion of the production fields and are used for irrigation water supply

Buffer areas exist around much of the site. This is a beneficial feature that has the potential to help protect receiving waters from runoff leaving the farm. This feature should be taken into account in selecting and designing water quality protection practices for the site.

Step 2. Develop master site map

Step 3. Select in-field BMPs

Site-specific characteristics and features, such as the natural drainage pattern in the field, the locations of permanent irrigation pipelines and hydrants, and alternative runoff receiving areas, should be considered in determining row orientation. Because this is a newly acquired farm without an existing irrigation system, row orientation is not constrained. The irrigation system can be designed concurrently with the water quality protection plan. The natural drainage pattern in field 1 indicates that concentrated flow occurs in that field. An effective option is the establishment of a grassed waterway, as shown in Figure 5.3, and orientation of the rows so that they drain toward the waterway. The waterway can then transport the runoff from the field to the southeast pond. The grassed waterway will be designed, established, and maintained as recommended in practice standard NRCS 412.

The natural drainage pattern of field 2 discharges runoff to both the eastern and southern edges of the field. Orienting the rows as shown in Figure 5.3 would take advantage of the existing buffers adjacent to the southern edge of the field and would also result in shorter rows, which would reduce sediment loss as compared to longer rows.

For fields 3 and 4, rows can be laid out across the dominant slope, as illustrated in Figure 5.3. In both cases, the runoff will be directed into the existing buffer areas, which are wide enough (at least 100 ft) to treat the runoff before it reaches the creeks. An initial site inspection may show existence of concentrated flow paths, indicating that level spreaders are needed to ensure that the runoff enters the buffer areas as dispersed flow. Inspection during runoff events will indicate if the flow is adequately dispersed when entering the buffer area.

Additional in-field BMPs that will be implemented in all fields include drip irrigation, irrigation scheduling, cover crops, and deep tillage. Off-season cover crops will be planted in the fall throughout the fields to reduce runoff, sediment, and chemical loss during the winter and early spring. Inter-row areas will be seeded with suitable grass cover in the spring, following deep tillage. Precision land forming will be implemented in field 2 to ensure that runoff drains readily from the field.

Step 4. Select and design off-site BMPs

• Field borders will be installed perpendicular to the rows. All field borders should be at least 30 ft wide except at the downslope end of the rows, where they should be 60 ft wide. Equipment traffic will not be allowed on the lower 30 ft of the 60-ft wide border.
• The riparian buffers that currently exist along North and South Creeks and the marsh vary in width from approximately 100 to 500 ft. If field runoff is distributed as uniformly as possible across these buffers, they will be very effective in trapping sediment and sediment-bound pollutants and in infiltrating dissolved pollutants.
• Level spreaders will be used as needed in conjunction with the buffer areas for maximum performance. The effectiveness of the level spreaders plus buffers will be enhanced by forcing runoff from the inter-row areas to flow directly into the adjacent field borders and forested buffers without combining with the flow from other inter-row areas.

Step 5. Develop integrated pest management (IPM) program

• Succulent Vegetables, Inc. has developed economic thresholds for each type of pest that may be encountered.
• A professional IPM scouting service has been contracted to provide scouting services and to make pesticide application recommendations. This is in addition to daily scouting that the grower will conduct. Scouting reduces unnecessary pesticide applications if an infestation has not reached a critical economic threshold.
• A crop rotation system will be developed based upon the crops grown and the ownership status of the land.
• High quality, disease free transplants will be used to reduce disease populations and pesticide use.
• Windbreaks will be planted parallel to the bed direction in locations where wind damage could occur to protect young transplants from wind erosion damage and resulting bacterial and fungal infections.
• Only pesticides labeled for the crop grown will be used. All pesticides used will be applied in conformance with application and environmental risk restrictions on the product's label. Waterbody setbacks and application restrictions related to impervious surfaces, including the plastic mulch, will be strictly followed.
• Cost-effective pesticides with minimum environmental risks will be selected whenever possible.
• Specialized directed spray-rigs will be used to apply pesticides directly to the plant to minimize drift and overspray.

Step 6. Develop nutrient management plan

Step 7. Develop irrigation/chemigation management plan

Step 8. Develop implementation schedule and maintenance plan

Step 9. Determine cost of plan implementation and operation

Step 10. Finalize water quality protection plan

Alternative (a):
Orienting the rows across the slope as shown in Figure 5.3 and discussed previously.
Alternative (b):
Alternative (a) except orienting the rows with the slope in field 3, as shown in Figure 5.4. This would require that the runoff be transported by the ditch at the eastern edge of the field to an appropriate structure before dispersal into the buffer area. The structure could be either a level spreader or a detention basin. Both alternatives should be designed and evaluated in terms of cost and practicality.
Alternative (c):
Alternative (b) except orienting the rows in field 2 along the length of the field. Most of the runoff from the field would flow into the southern pond. This pond also drains the interior portion of field 1. The 2-year, 24-hour storm for this alternative results in 7.92 acre-ft of runoff. This requires approximately 1.5 ft of design wet weather storage above the permanent pool level. This is feasible for the southern pond and the principal spillway will be redesigned to dewater this volume of water in 60 hours, as described in Table 2.6. The principal spillway orifice required to dewater 7.92 acre-ft in 60 hours is 8.4 in. (calculated with procedures in Table 2.6). Outflow from the southern pond will be dispersed into adjacent forested buffers using a level spreader in accordance with the Erosion and Sediment Control Handbook Standard for Level Spreaders (VESCH 3.21) for the 2-year, 24-hour duration storm rather than the 10-year, 24-hour duration storm.
Alternative (d):
Alternative (c) except orienting the rows in field 4 with the slope. This would result in runoff from field 4 flowing into field 1 and being transported by the grassed waterway into the southern pond. This alternative would require the waterway, as well as the principal spillway and level spreader, to be larger. This alternative would also result in the longest rows on all four fields and potentially produce the most runoff and erosion.

From a water quality perspective, the combination of BMPs described as alternative (a) would be the best choice. With costs taken into account, alternative (b) may be a preferred plan.

5.2 Example Water Quality Protection Plan - Northern Neck

Step 1. Collect Data

Slopes in the field are very slight and average approximately 1%. Elevation ranges from 10 to 15 ft. The following detailed descriptions of the production field soils were obtained from the county soil survey.

• PAMUNKEY FINE SANDY LOAM - Pamunkey fine sandy loam is deep, nearly level, and well drained. Erosion hazard is slight for water and moderate for wind. Cultivated crops and nursery stock are moderately well suited to this soil. This soil will contribute to the leaching of fertilizer below the root zone unless intensive nutrient management is applied. Hydrologic soil group B. Soil erodibility factor = 0.28. Depth to water table is approximately 3 to 4 ft.
• BOJAC SANDY LOAM, 0 TO 2 PERCENT SLOPES - Bojac sandy loam is nearly level, very deep, and well drained. Erosion hazard is slight for water and wind. This soil is prime farmland. It has few limitations for commercial use. Cultivated crops, nursery stock, pasture grasses, and legumes are well suited to this soil. This soil will contribute to leaching fertilizers below the root zone unless intensive nutrient management is applied. Hydrologic soil group B. Soil erodibility factor = 0.24. Depth to water table is approximately 4 to 6 ft.
• TETOTUM LOAM, 0 TO 2 PERCENT SLOPES - Tetotum loam is nearly level, deep, and moderately well drained. Erosion hazard is slight for water and moderate for wind. This soil has some limitations for agricultural and commercial use due to a seasonal high water table. Cultivated crops and nursery stock are moderately suited to drained areas. Pasture grasses, legumes, and timber are more suited to this soil. This soil may contribute to leaching of fertilizer below the root zone. Hydrologic soil group C. Soil erodibility factor = 0.32. Depth to water table is approximately 1.5 to 2.5 ft.
• LENOIR SILT LOAM ­ Lenoir silt loam is deep, somewhat poorly drained, and nearly level. Erosion hazard is slight for water and wind. The soil is moderately well suited to cultivated crops and well suited to pasture. The soil may contribute to leaching fertilizer below the root zone. Hydrologic soil group D. Soil erodibility factor = 0.37. Depth to water table is approximately 1.0 to 2.5 ft.

Environmentally sensitive areas adjacent to the production fields include the tidal creek and the forested riparian zone along its shoreline, and the Rappahannock River with its estuarine marshes. There is also a drainage ditch parallel to the county road that will transport any entering runoff directly to the creek and river, which are water sources for the irrigation systems. A narrow forested buffer exists to the north and northeast of the property along the creek.

Step 2. Develop master site map

Step 3. Select in-field BMPs

The two constraints are the almost negligible slope in the fields and the locations of the existing permanent irrigation water supply lines. In field 1, underground submains and hydrants dictate that headers be installed perpendicular to the county road. Additionally, the almost negligible slope in these fields requires that rows be oriented up and down the slope to facilitate drainage from the fields (Figure 5.7). In field 1, orienting rows in this manner parallel to the county road will further insure that little field runoff will be directly contributed to the ditch. For field 2, orienting the rows with the slope results in discharge directly to the county road ditch and in the direction of the road culvert.

Additional in-field BMPs that will be implemented in all fields include cover crops and deep tillage. Off-season cover crops will be planted in the fall throughout the fields to reduce runoff, sediment, and chemical loss during the winter and early spring. Inter-row areas will be seeded with suitable grass cover in the spring, following deep tillage.

Irrigation scheduling will be implemented in both fields, and is especially critical in field 2. The overhead irrigation system will likely result in more runoff compared to a drip irrigation system. In addition, nutrients should only be applied through the irrigation system when the crop needs water. The chemigation plan must consider these limitations.

Step 4. Select and design off-site BMPs

The off-site BMPs that will be implemented are the following:

• Field borders are a key BMP at this site. At the northern edge of field 1, a 60-ft wide border will be installed perpendicular to the rows. This will help stabilize the road ditch and disperse runoff before it flows across the road into the buffer area. Permanent vegetation will be established in the far northeast corner of field 1 to reduce the possibility of runoff flowing directly to the creek without any treatment. All other field borders should be at least 30 ft wide; borders at the downslope end of the rows should be at least 60 ft wide. Equipment traffic will not be allowed on the lower 30 ft of the 60-ft wide border.
• The eroded gully just beyond the northeast corner of field 1 will be graded, vegetated, and maintained as a grassed waterway. A culvert will be installed to pass water from the waterway to the creek without flowing over the road. The runoff entering the creek via the waterway should be of acceptable quality because of the in-field practices and field borders. The road cannot be relocated due to existing facilities and property boundaries.
• The riparian buffers that currently exist along the tidal creek north of field 1 vary in width from approximately 50 to 75 ft. The 60-ft wide field border that will be established along the northern end of field 1 will enhance the effectiveness of the riparian buffer. In addition, measures, such as additional plantings, should be applied within the riparian buffer itself to encourage denser vegetative cover.
• Level spreaders will be used as needed in conjunction with the buffer areas for maximum performance. The effectiveness of the level spreaders plus buffers will be enhanced by forcing runoff from the inter-row areas to flow directly into the adjacent field borders and forested buffers without combining with the flow from other inter-row areas.
• A diversion will be installed to prevent runoff from field 3 from entering field 1. The diverted runoff from field 3 should be properly treated and dispersed before discharging to the buffer area along the creek.

Step 5. Develop Integrated Pest Management (IPM) Program

• Palatable Produce, Inc. has developed economic thresholds for each type of pest that may be encountered.
• A professional IPM scouting service has been contracted to provide scouting services and to make pesticide application recommendations. This is in addition to daily scouting that the grower will conduct. Scouting reduces unnecessary pesticide applications if an infestation has not reached a critical economic threshold.
• A crop rotation system will be developed based upon the crops grown and the ownership status of the land.
• High quality, disease free transplants will be used to reduce disease populations and pesticide use.
• Windbreaks will be planted parallel to the bed direction in locations where wind damage could occur to protect young transplants from wind erosion damage and resulting bacterial and fungal infections.
• Only pesticides labeled for the crop grown will be used. All pesticides used will be applied in conformance with application and environmental risk restrictions on the productıs label. Waterbody setbacks and application restrictions related to impervious surfaces, including the plastic mulch, will be strictly followed.
• Cost-effective pesticides with minimum environmental risks will be selected whenever possible.
• Specialized directed spray-rigs will be used to apply pesticides directly to the plant to minimize drift and overspray.

Step 6. Develop nutrient management plan

Step 7. Develop irrigation/chemigation management plan

Step 8. Develop implementation schedule and maintenance plan

Step 9. Determine cost of plan implementation and operation

Step 10. Finalize water quality protection plan

This example illustrates that a water quality protection plan needs to be monitored after implementation to determine if it is working as planned. Modifications may be required over time.

5.3 Example Water Quality Protection Plan - Southwest

Step 1. Collect Data

Crop production on the farm is very diverse with both perennial small fruits and annual vegetable crops raised on the farm. Drip irrigation is used on all crops, including a small fruits orchard in which plastic mulch is not used, located in the smallest field shown on the map. Plastic mulch is used for some annual vegetable crops and one row-cropped, perennial small fruit crop. Additionally, for the latter, an overhead irrigation system is used solely for frost protection. All water for drip irrigation and frost protection is supplied by a groundwater well located on the farm.

Slopes in the field are moderate to steep and range from 5% to 20%. Elevation averages approximately 2000 ft. The following detailed descriptions of the production field soils were obtained from the county soil survey.

• GROSECLOSE SILT LOAM, 2 TO 7 PERCENT SLOPES - These soils are well drained and gently sloping on ridgetops. Erosion hazard is moderate. Cultivated crops, pasture grasses, and legumes are well suited to these soils. Hydrologic soil group C. Soil erodibility factor = 0.43. Depth to water table is greater than 6 ft.
• GROSECLOSE SILT LOAM, 15 TO 25 PERCENT SLOPES - These soils are well drained and moderately steep. Erosion hazard is severe. These soils are used mainly for pasture and woodland. Soil conservation measures are necessary for cultivated crops, which are poorly suited to these soils. Hydrologic soil group C. Soil erodibility factor = 0.43. Depth to water table is greater than 6 ft.
• FREDERICK SILT LOAM, 7 TO 15 PERCENT SLOPES - These are well drained, strongly sloping soils on ridgetops and side slopes. Erosion hazard is moderate. Cultivated crops are well suited to these soils. Hydrologic soil group B. Soil erodibility factor = 0.32. Depth to water table is greater than 6 ft.

There are no perennial streams, either through or adjacent to the property. An intermittent stream, framed by an herbaceous buffer of varying width and vegetative quality, is located to the east of the production fields. No surface drainage ditches or other artificial drainage measures are necessary because of the pronounced field slopes. No environmentally sensitive areas are identified in the immediate vicinity of the production fields. The private homes, and associated domesticwater supplies, to the northwest of the farm should not be impacted, from a water quality standpoint, by the downgradient crop production activities.

Step 2. Develop master site map

The production diversity of the farm allows some flexibility in relegating crop production posing greater runoff and erosion hazards to those fields (and soils) with less runoff and erosion potential. For example, perennial small fruit orchards, grown without plastic mulch and involving minimal soil disturbance, should be located where runoff and erosion potential is greatest (assuming that recommended measures, such as vegetated alleyways, are implemented). Conversely, fields/soils having less runoff and erosion potential should be reserved for crops with plastic mulch, and, in particular, where frost protection by overhead sprinklers is used. While this represents a water quality protection viewpoint only, other factors, such as air drainage and field aspect considerations, public access and harvesting schedules, and crop rotation patterns, will need to be taken into account.

For the purposes of this proposed plan, the small fruit row crop with plastic mulch and overhead sprinkler frost protection will be produced in field 1 (predominately Groseclose silt loam, 2 to 7% slopes), and various row-cropped vegetables, both with and without plastic mulch, will be grown in field 2 (predominately Frederick silt loam). The field that has the greatest runoff and erosion potential (predominately Groseclose silt loam, 15 to 25% slopes) currently contains the small fruits orchard in which plastic mulch is not used.

Step 3. Select in-field BMPs

The first in-field BMPs that should be considered are contour farming and row direction. Contour farming should be selected, if feasible, and will be implemented in field 2. For field 1, orienting rows across the slope, designated ³row direction² BMP in this handbook, is proposed.

Site-specific characteristics and features, such as the natural drainage pattern in the fields, the locations of permanent irrigation pipelines and hydrants, and possible runoff receiving areas, should be considered in determining row orientation. In this case, all irrigation supply lines are portable and aboveground, so they do not constrain the desired row orientation.

The magnitude of the field slopes dictates that rows be run across the slope with sufficient cross slope incorporated to allow drainage of the inter-row areas. In some situations, it may be possible to orient the rows so that field drainage can exit either side of the field to take advantage of natural drainage patterns which will not only treat runoff but direct it around, and not through, downslope production areas. Proposed row directions for fields 1 and 2 are indicated in Fig. 5.10.

Additional in-field BMPs that will be implemented in fields 1 and 2 include cover crops and deep tillage. Off-season cover crops will be planted in the fall (where applicable) throughout the fields to reduce runoff, sediment, and chemical loss during the winter and early spring. Inter-row areas for annual crops will be seeded with suitable grass cover in the spring, following deep tillage.

Irrigation scheduling for frost protection is critical in field 1 because use of an overhead irrigation system leads to the potential for increased runoff and leaching. The irrigation/frost protection system should be specifically designed not to apply water at a rate greater than that required and run only when, and to the extent, necessary to counter freezing temperatures and conditions that may incur frost/freeze damage.

Step 4. Select and design off-site BMPs

• The current layout of the farm fields provides adequate room for field borders to be established and maintained without taking any existing cultivated land out of production. Therefore, permanent vegetation will be established and maintained in all inter-field areas. In the outer field perimeter areas, all field borders should be at least 30 ft wide; borders at the downslope end of the rows should be at least 60 ft wide. Equipment traffic will be allowed only within the first 30 ft of the field borders from the edge of the field and remain out of the drainageways. Access roads will not be routed along drainageways and cross them only where necessary.
• The primary drainageway, between field 2 and the small fruits orchard, will be established and maintained as a grassed waterway. Access roads will not cross the grassed waterway. The grassed waterway will be designed, established, and maintained as recommended in practice standard NRCS 412.
• The riparian buffer that currently exists along the intermittent stream east of field 2 varies in width from approximately 50 to 75 ft. The 60-ft wide field border that will be established along the eastern end of field 2 will enhance the effectiveness of the riparian buffer. The riparian buffer should be enhanced through vegetation management.
• Runoff from the private homes and lawns runs onto field 1. A diversion will be utilized to intercept and direct this runoff around the field and into the primary drainageway above the grassed waterway.

Step 5. Develop Integrated Pest Management (IPM) Program

• Pick-Your-Own Operations, Inc. has developed economic thresholds for each type of pest that may be encountered.
• The farm manager will conduct daily scouting for the purposes of recommending pesticide applications. Scouting reduces unnecessary pesticide applications if an infestation has not reached a critical economic threshold.
• A crop rotation system will be developed based upon the crops to be grown.
• High quality, disease free transplants will be used to reduce disease populations and pesticide use.
• Only pesticides labeled for the crop grown will be used. All pesticides used will be applied in conformance with application and environmental risk restrictions on the productıs label. Waterbody setbacks and application restrictions related to impervious surfaces, including the plastic mulch, will be strictly followed.
• Cost-effective pesticides with minimum environmental risks will be selected whenever possible.
• Specialized directed spray-rigs will be used to apply pesticides directly to the plant to minimize drift and overspray.

Step 6. Develop nutrient management plan

Step 7. Develop irrigation/chemigation management plan

Step 8. Develop implementation schedule and maintenance plan

Step 9. Determine cost of plan implementation and operation

Step 10. Finalize water quality protection plan

In field 2, a grassed waterway in the main drainageway of the field may provide additional water quality protection, if warranted. Field 2 also contains a mix of vegetable crops, some of which are produced with plastic mulch and some without. Initially, it appears that plastic mulch use limited to the upper field areas, where the slopes are somewhat milder and the travel distance of runoff is greatest, would perhaps lead to a reduction in the amount of runoff and soil leaving the farm. Given crop rotation constraints, experience over time, however, will help determine exactly where in the field plastic mulch use will result in the least environmental impact.

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Technical References

1. Arnold, G., M. Luckenbach, M. Roberts, Jr., M. Newman, E. Shumann, M. Unger, and G. Vadas. 2001. Fate and effects of crop protectants from tomoato cultivation on living resources in tidal creeks. Draft Final Report submitted to Virginia Department of Agriculture and Consumer Services, August 2001.
2. ASAE Standards 2001. 48th Edition. ASAE, St. Joseph, MI.
3. Coble, H. Determining the Practice of Integrated Pest Management (IPM): A Working Definition for the Year 2000 Goal. Accessed at: www.ipm- education.org/papers/coble012099.html, June 26, 2001.
4. Commercial Vegetable Production Recommendations - Virginia, 2001. Virginia Cooperative Extension. Publication No. 456-420.
5. NRCS Conservation Practice Standards. Available online at www.ftw.nrcs.usda.gov/practice_stds.html
6. Pest Management Guide: Horticultural & Forest Crops - Virginia, 2001. Virginia Cooperative Extension. Publication No. 456-017.
7. Virginia Conservation Practice Standards. Available online at www.va.nrcs.usda.gov/DataTechRefs/std_specs.htm
8. Virginia Erosion and Sediment Control Handbook. Third Edition, 1992. Virginia Department of Conservation and Recreation. Division of Soil and Water Conservation, Richmond, Virginia.

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Appendix A Financial Programs

Additional programs target erosion and water quality, enhance habitat for wildlife, and encourage good forest stewardship. Each conservation program has specific requirements and some have limited sign-up dates. Conservation incentive programs are constantly changing so it is advisable to contact the Natural Resources Conservation Service (NRCS), the Farm Service Agency (FSA), Virginia Cooperative Extension (VCE), Virginia Department of Conservation and Recreation (DCR), and/or the local Soil and Water Conservation District (SWCD) office to receive the latest information on these and other programs. Contact information for these agencies is included in Appendix C. The programs described briefly below were some of the programs available at the time this handbook was printed.

Programs administered by NRCS

Wildlife Habitat Incentives Program (WHIP). This is a voluntary program for people who want to develop or improve wildlife habitat on private lands. Cost-share assistance up to 75% is available for establishing habitat. WHIP agreements between NRCS and the participant generally last from 5 to 10 years from the date the agreement is signed.

Wetland Reserve Program (WRP). This program is available to qualified landowners statewide to restore wetlands. Sign-up is on a continuous basis. Landowners who choose to participate in WRP may receive payments for a conservation easement or cost-share assistance for a wetland restoration agreement. The landowner retains ownership but voluntarily limits future use of the land.

Emergency Conservation Program (ECP). In the event of a natural disaster, ECP may be implemented to rehabilitate farmlands and conservation facilities. ECP provides cost-share assistance to eligible producers. The Farm Service Agency and the Natural Resources Conservation Service administer this program.

Programs administered by FSA

Conservation Reserve Enhancement Program (CREP). This voluntary program uses financial incentives to encourage farmers and ranchers to enroll in the Conservation Reserve Program (CRP) with contracts to remove lands from agricultural production. The Virginia enhancement program consists of two components: the Chesapeake Bay CREP and the Southern Rivers CREP. When fully implemented, these projects will collectively restore up to 30,500 acres of riparian habitat and 4,500 acres of wetlands. One project will target 25,000 acres within the Bay watershed, while a second project will target 10,000 acres in non-Bay drainage basins.

Programs administered by SWCDs

Virginia Agricultural Best Management Practices Tax Credit Program. This program provides an incentive to voluntarily install agricultural best management practices (BMPs) in accordance with an approved conservation plan. The local SWCD Board must approve the tax credit before the BMP is installed. Another goal is to reduce the amount of nonpoint source pollution entering the state's streams, rivers, and estuaries. This program is applicable to all land within the Commonwealth. Agricultural producers with an approved conservation plan can take a credit against their state income tax in the amount of 25% of eligible BMP expenses, not to exceed $17,500. If the credit is in excess of the total state income tax obligation for the given tax year, producers may carry over the credit for up to five years.

Virginia Conservation Equipment Tax Credit. The Department of Conservation and Recreation (DCR), in conjunction with the local SWCD, administers this program. It applies statewide and may be claimed for the year of purchase for equipment meeting state-approved specifications. To be eligible for the equipment tax credit, the applicant must have a nutrient management plan approved by the SWCD. Categories of equipment potentially eligible for the credit are sprayers for pesticide and liquid fertilizers, pneumatic fertilizer applicators, manure applicators, tramline adaptors, and starter fertilizer banding attachments for planters. The above listed items qualify for a tax credit equaling 25% of the equipment purchase price or $3750, whichever amount is less. Conservation tillage equipment is eligible for a 25% tax credit, not to exceed $2500. The equipment must meet state established criteria, and the producer must have a nutrient management plan approved by the local SWCD.

Program administered by the Virginia Department of Environmental Quality

Program administered by the Virginia Department of Business Assistance