• Nitrogen content of green crops

      Ottman, Michael J.; Husman, Stephen H.; Ottman, Michael (College of Agriculture, University of Arizona (Tucson, AZ), 2000-10)
      Application of chemical fertilizer is not permitted in production of crops certified as organic, but green manure crops may be used to supply the nutrient needs of these crops. An experiment was conducted on a commercial farm near Litchfield Park to determine the nitrogen content at plowdown of barley mixed with Austrian winter peas, Magnus peas, and/or Lana woolleypod vetch. The crop was planted on 21 October and sampled for plowdown nitrogen content on 1 March. The peas and vetch comprised less than 10% of the dry weight of the mixture since the barley grew more vigorously. The barley contained 66 lbs N/acre in the forage while the legumes in the mixture contained 16 lbs N/acre on average. The amount of N in the green manure, even if 100% was available, was not enough to supply the needs of a 2 bale/acre organic cotton crop. The planting date, plowdown date, or species composition in the green manure mixture needs to be altered for green manure to supply the N needs of organic cotton.