Recycle Old Plasticulture Fields With A New Production System
Commercial Horticulture Newsletter, November - December 1996
Charlie O'Dell, Extension Horticulturist, Vegetables
Department of Horticulture
Virginia Tech
Blacksburg, VA 24061-0327
Background/Abstract
Currently there are relatively few acres of strawberries in Virginia, but many acres of plasticulture vegetables. Nationally and internationally plasticulture production is a growth industry, but concerns about dumping plastic in landfills plus labor and cost of removing plastic and recovering plastic mulched fields are drawbacks, the downside of plasticulture. The purpose of this work was to develop a system for recycling plasticulture inputs and land preparation while reducing labor and fertilizer nutrients to produce a second or third crop from land in previous plasticulture enterprises.
Key components of this production system are: 1) soil testing of previously cropped rows beneath the mulch film to determine nutrient needs for a subsequent crop; 2) nutrient needs of a subsequent crop are determined from soil test rec's for vegetable crops, table 8, 46 Enterprises, VCE Pub. 456-420 published annually (use soil test fertilizer rec's developed for your area); 3) use only 1/2 the published broadcast rates since about 1/2 of the area of a plasticulture field is covered by mulch film; 4) fertigation of needed nutrients is divided into 3 applications through the drip system beneath the mulch film based on crop cycle/sidedress needs; 5) plant nutrient levels are monitored by tissue analysis or petiole sap ion meter; and, 6) little nitrogen application is made before fruit set of a subsequent crop. A highly profitable pumpkin crop was produced by this production system recycling both 2 year and 1 year plasticulture strawberry production inputs while conserving expensive fertilizer nutrients, plastic, landfills and labor.
Materials and Methods
On old Chandler strawberry research plots, 2 harvest years and 1 harvest year at our Kentland Research Farm near Blacksburg, berry plants and row middles weed growth were killed in mid-June with Gramoxone. Previous season non-cucurbit vegetable plasticulture fields such as those in tomatoes, peppers and others also could be held over and recycled in similar fashion (see Table 1). Fall pumpkins were seeded July 1 on the recycled plastic mulch and drip tape. Two seeds of Howden, Harris Moran select strain and a new variety, Howden Biggie, were planted 3" from the centered drip tape every 3 feet apart in-row. After emergence all "hills" were hand-thinned to 1 plant every 3' in-row. Plot rows were on 6' centers. 2 rows each 90 ft. long were selected from both 2 year and 1 year beds. Each test was .025 or 1/40 of an acre in size. From both tests four 12 feet long row lengths were staked out before seeding as data collection replicates. Crop protectant fungicides Bravo plus Bayleton were applied every 14 days from late July through September using a high capacity FMC airblast sprayer with row crop heads, spraying both sides of plots equal to a spray lane after every 5 rows. Once per month we used Ridomil/Bravo 81W plus 2 oz./A rate of Bayleton in lieu of the above program. An IPM approach was used to apply Thiodan for Cucumber Beetles and Squash Bugs only as adults were seen. Perhaps because the plots were isolated 3/4 of a mile away plus 400' higher elevation than other veg. research plots or because of planting late on black plastic to avoid mature pumpkins before the fall season, we saw no Cucumber Beetles or Squash Bugs. For Pickleworm control, preventative Thiodan sprays (before larvae penetrate rinds) were applied 3 times, early, mid and late September tank mixed with the fungicide program.
Prior to planting, soil tests were taken from beneath the plastic mulch in rows of both the 2 year and 1 year Chandlers. After 2 harvest years of strawberries, both phosphate and potash were low plus (or medium minus) in old beds. In the 1 year berry beds phosphate was high minus while potash was medium minus. Both sets of beds had received primarily only nitrogen fertigations during previous spring strawberry crops. For old 2 year beds, a fertigation program was selected using 1:1:1: ratio of N:P:K from 20-20-20 soluble fertilizer with minor elements to fertigate 20 lbs./acre each of N:P:K/acre 3 times at 3 week intervals starting when, but not before, pumpkin vines began to run. Fertigation dates were July 25, August 19 and Sept. 9.
A total of 60 lbs./acre of N, P and K was applied during the fruit set/development stage of plants on the old 2 year beds (equal to 120 lbs./acre broadcast). On the 1 year berry beds, the fertigation program was also based on soil tests of those beds using a 1:1 ratio of N and K. 15-0-15 high calcium was used, also weighed to supply 20 lbs. of N and K/acre per fertigation for each of the 3 fertigations, 60 lbs. total N and K per acre for the season (equal to120 lbs./acre broadcast). Between the 3 scheduled fertigations of both tests extra drip irrigations were made by tensiometer whenever available soil moisture in the beds fell below 70%, which with the cool, wet summer was infrequent. As pumpkin vines ran, they rooted in soil between plastic strips thereby extracting additional moisture above that supplied to the beds by the drip irrigation system. No fertilizer nutrients were supplied to row middles in this test or to middles during previous strawberry tests.
Results
Let's look at the harvest data from the growers'
point of view: From the total harvests on old beds, I had 92
pumpkins averaging 21 lbs. each (across both varieties), total
wt. of 1,932 lbs. X wholesale value of (at least) .10/lb. = $193.
grower value X 40 = $7,720 per acre projected. From the 1 year
beds I had 82 pumpkins with ave. wt. of 26 pounds (across both
varieties), total wt. of 2,132 lbs. X wholesale value of .10/lb.
= $231. grower value X 40 = $9,240 per acre projected. Remember,
there were no investments for land preparation, bedding, mulch
purchase and laying, drip irrigation system purchase and
installation or labor of hooking up to water supply and very low
pre-harvest labor inputs by "recycling" these production inputs
to improve grower profitability!
As berry and veg. growers tighten row center spacings (example,
turning rims on rear tractor wheels allows us to go from 6' row
centers to 5' row centers for 1997) a future research
question needs answers: Can we go 5' X 3' to get more fruit
numbers per acre, with fertigation to get similar good fruit
size? (2,904 plants/acre versus 2,420 at 1996 3' X 6'
tests). Can we go to 2.5' in-row X 5' centers plant spacing =
3,484 plants/acre and still, by careful management of drip
irrigation and fertigation, maintain fruit size and quality?
That may be pushing the limits, but we love that challenge. We
will let the data of such future tests do the talking! Special
thanks to Drs. Robert Rouse and Charles McClurg, Extension
Horticulturists at University of Maryland, for sharing their
reference materials and research results of pumpkin production on
old plasticulture strawberry beds which indicated subsequent
crops fertigation rates should be based on soil tests of the
previously cropped plasticulture rows or beds.
Trade names are used in this publication for information purposes
only. Virginia Cooperative Extension, Virginia Polytechnic
Institute and State University, and Virginia State University do
not warrant those mentioned nor do they intend to imply
discrimination against those not mentioned.
Table 1. Some Possible Plasticulture Recycling Crop Sequences.
Spring Crop (or previous year) Fall Crop Strawberries (2 rows/bed) Tomato, summer squash,
cukes, beans, pumpkins Melons Tomato, cole crops Sweet corn (2 rows/bed, mech. seeded) Summer squash, tomatoes,
or cucumbers Peppers (2 rows/bed) Summer squash, cucumbers,
or cole crops Tomatoes Cucumbers, summer squash,
or cole crops Summer squash Tomato, cole crops, snap
beans Cucumbers Tomato, snap beans, cole
crops Eggplant Summer squash, snap beans Cole crops (2 rows/bed) Summer squash, pumpkins,
melons, tomato, beans Snap beans (2 rows/bed) Pumpkins, summer squash,
cukes, melons Early Southern peas Pumpkins, summer squash,
cukes, melons, tomato Lettuce (2 rows/bed) Pumpkins, sweet corn,
melons, squash, tomato