Most research in the USA has shown that soybean grown on US soils do not respond to fertilizer nitrogen (N). A few positive responses have been reported when soybean was grown under drought in the southern US, when N was applied after flowering, and when biosolids were added. In a published two-year study in north Texas on a high pH calcareous soil, we found low N concentrations in soybean forage. Consequently, we initiated a second study to determine whether selected soil-applied N sources might increase forage N concentration or soybean yield. In 2003, N was applied as ammonium nitrate up to 112 kg N per ha and dairy manure compost was applied at rates of 5, 10, 15, and 20 Mg per ha. In 2004, ammonium nitrate was applied at rates of 112 and 224 kg per ha and dairy manure compost was applied at 32 and 64 Mg per ha. The dairy manure compost contained 5.9, 2.6, and 6.7 g per kg N, P, and K respectively. In another 2004 test, biosolids were applied at 10 Mg per ha and a biosolids/municipal yard waste compost mixture was applied at 58 Mg per ha. The biosolids contained 31, 18, and 2.9 g per kg N, P, and K, respectively. The mixture contained 8.8, 6.1, and 3.4 g per kg N, P, and K, respectively. None of the soil treatments affected soybean grain yield or forage N concentration.
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