EVALUATION OF THE NITROGEN-FERTILIZER VALUE OF PLANT MATERIALS TO SPRING WHEAT PRODUCTION

Use of green manure crops has become a preferred alternative source of N. The objectives of this 3-yr field study were to evaluate the N sup plying power of 1, 2, and 3 Mg ha-1 of Austrian winter pea (Pisum sati vum ssp. arvense (L.) Poir), alfalfa (Medicago sativa L.), and wheat ( Triticum aestivum L.) residue. Residues were incorporated in September and the N contribution of each amendment to a subsequent spring wheat crop was calculated. We measured inorganic soil N levels and wheat yi elds in northern Idaho on Latahco silt loam (fine-silty, mixed, mesic Pachic Ultic Haploxeroll) soils. Soil samples were taken during July o f each year to determine residual inorganic N. Plant material addition and incorporation affected spring wheat yield and soil inorganic N le vel in each study. Pea and alfalfa material applied at 3 Mg ha-1 resul ted in the highest spring wheat yields. Austrian winter pea residue at 3 Mg ha-1 provided a N credit of 51 to 63 kg ha-1 to spring wheat, co mpared to 1 to 36 kg ha-1 for alfalfa applied at the same rate. Based on inorganic soil N in July, application of 3 Mg ha-1 of Austrian wint er pea, alfalfa, and wheat residue provided an N credit of 16 to 24, 2 1 to 26, and -1 to -25 kg ha-1, respectively. Average total N credits (soil+plant uptake) for the 3 Mg ha-1 application of Austrian winter p ea, alfalfa, and wheat materials were 76, 47, and -35 kg ha-1, respect ively. Estimated N recovery of Austrian winter pea material after 10 m o of incorporation was 77% (58% in wheat and 19% in soil).