Relative effects of ammonia and nitrite on the germination and early growth of aerobic rice

摘要: Recent studies have documented adverse affects of urea on the establishment and growth aerobic rice when applied at seeding. The following experiments were conducted to examine relative importance ammonia nitrite (NO) toxicities as mechanisms contributing poor germination early rice. Soil was collected from an experiment in Philippines where grown continuously for 7 years. Subsamples soil were: (1) pretreated with sulfuric acid (0.5 M H2SO4 added 75 mL kg–1), (2) oven-heated 120°C 12 h, or (3) left untreated. In a greenhouse study N untreated, acidified, soils either ammonium sulfate (0.0 0.3 g N kg–1). Plant height, root length, total biomass, number seminal roots evaluated after 10 d. Microdiffusion incubations used assess effects pretreatment, source, rate (0, 0.5, 1.0, 1.5 N kg–1) (NH3) volatilization germination. Nitrite establish critical level NO toxicity measure extractable trends affected by rate. On untreated soil, reduced while caused no effects. Progressively higher rates increased NH3 inhibited germination, oven-heating acidification minimized All treatment combinations (soil rate) had levels below 0.2 N kg–1, suggesting that not principal cause inhibition. Since risk is highest just hydrolysis, strategies optimize timing placement should be considered.