Sustainable Practices for Vegetable Production in the South
Dr. Mary Peet, NCSU
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1. Harvest the above-ground part of the cover crop from a 1 square foot section of the field, dry it, and weigh it. In a conventional oven, the sample should be dried at 112 degrees F for 2 to 5 days.
2. To find biomas in pounds of dry matter per acre, multiply dry weight x 43,560
3. Calculate N content of the cover crop per acre according to the following formulas: Rye: N = .0174 X biomass - 17.4 Hairy vetch: N = .0368 X biomass - 3.1 Crimson clover: N = .0183 X biomass + 13.8 Austrian winter pea N = .0362 X biomass - 9.2 Caley peas: N = .0383 X biomass - 6.1 Subterranean clover: N = .0252 X biomass + 2.9
4. For legumes, on average, pounds of potassium (k) = pounds of nitrogen (N), and pounds of phosphorus (P) = 10 percent pounds N.
EXAMPLE - A one square foot plot in a field of rye was cut to the ground shortly before the rye was to be turned under. The rye was dried in the oven and weighed. It weighed .12 pounds. Biomass (lbs dry matter/acre) = .12 x 43,560 = 5227.2 lbs/acre Nitrogen = .0174 (5227.2) - 17.4 = 73.6 lb N available / acre Potassium (K) - approximately 73 pounds per acre Phosphorus (P) = approximately 7.3 pounds per acre.