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Abstract: Nitrogen in the organic, synthetic organic, ammonium and nitrate forms was added to mushroom composts in two experiments by supplementing at first turn with dried blood nitroform (ureaformaldehyde), sulphate of ammonia and calcium nitrate. The fertilizers were applied at 0, 6 and 9 lb N equivalent per ton of fresh manure. A third experiment compared nitrogen from three sources (dried blood, cottonseed meal, nitroform) at four rates of application (0, 3, 6 and 9 lb N). Compost was analysed for nitrogen and ammonia during peak heating and before spawning and yields were recorded for the first six weeks of cropping. Sulphate of ammonia supplementation with or without ground limestone, gave no increase in the nitrogen content of compost but raised the ammonia content and depressed yield. Nitroform addition increased the nitrogen content of compost without raising the ammonia level, but had no effect on yield Calcium nitrate supplementation did not affect either nitrogen or ammonia content of the compost or yield. Yield increased with increasing rates of dried blood application m two of the three experiments. In one experiment, a high incidence of Chaetomium spp. was associated with dried blood supplementation. Cottonseed meal gave yields comparable to the dried blood treatments, but a proprietary mixture (6 percent organic N) depressed yields slightly. High Kjeldahl nitrogen contents were only associated with high yields when the nitrogen added was mainly in the protein form e.g. dried blood. Using dried blood, yields were increased with nitrogen contents as high as 2.8 percent. In most cases, ammonia contents above 0.30 percent (expressed as decomposed protein) depressed yields.
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