Vegetable Growers News
March-April 2000, Vol. 7, No. 2
Charlie O'Dell, Extension Horticulturist
Department of Horticulture
Virginia Tech (0327)
Blacksburg, VA 24061
In recent area strawberry schools we have imported expertise from NCSU benefiting our growers from the latest applied field research by our next door neighbors. Dr. Gordon Miner, their soil scientist, works diligently with refining strawberry plant nutrient needs and optimizing times of application of fertigations through the drip irrigation system. He has developed a simple, New Way to manage spring fertigation needs. Strawberries primarily need nitrogen during a 12-week period beginning at first flush of re-growth in early spring as discussed in our strawberry guide, VCE Pub 438-018.
Especially where heavy bloom and strong fruit set occurs where clients have heavy fruiting crowns, yields over the past 2 years have been increased on Chandler, Sweet Charlie and Camerosa varieties by this new approach which gets the nitrogen levels up much faster on the front end of the bloom season where they must be for top yields and quality. Our standard recommendations in this region are for weekly or every other week applications of nitrogen at 0.5 lbs actual N per acre per day rate X number of days since last fertigation, usually once a week over a 12 week spring period. Normally we take an early leaf tissue sample and may begin with 5 pounds actual N per acre per week on the first fertigation, perhaps dropping to 3.5 lbs N/A once per week later, based on tissue levels.
The new system that may be of interest to your growers begins at first flush of re-growth in spring in each area of the state, certainly by first blooms appearance:
On sandy soils, apply 3 injections of 20 lbs. actual N per acre every 3 weeks, total of 60 lbs. N per spring season fertigated;
On medium heavier soils, apply 3 injections of 15 lbs. actual N per acre every 3 weeks, total of 45 lbs. per spring season;
On heavier silt and clay loams, apply 3 injections of 10-12 lbs. actual N per acre every 3 weeks, total of 30-36 lbs. N per spring season.
Ideally, tissue sampling should be done once every 3 weeks during this 12 week spring period, but we have no state tissue analysis lab service available. Some Virginia Extension agents, state specialists, and commercial Virginia strawberry growers have purchased Cardy petiole sap meters for nitrate-NO3 petiole sap measurements on a weekly basis, saving the $30./sample cost of commercial testing labs, paying for the $300. meter in 11 samples compared to commercial lab fees (Cardy NO3 ion meter, Spectrum Technologies, Plainfield, Ill., phone 800-248-8873). The sufficiency levels for petiole sap N03-N have been established by Dr. George Hochmuch in Florida for strawberries and commercial vegetable crops and in California by Dr. Tim Hartz. They confirm that this portable ion meter correlates very closely with results from their states' tissue testing labs. These tissue sufficiency levels for strawberries by stage of growth and fruiting are published in our Virginia strawberry production guide. Dr. Greg Welbaum and I have used these meters since the early 1990s with excellent results as a basis for making fertigation decisions on veg crops and strawberries.
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