Effect of source and nest size of N fertilizers and temperature on nitrification in a coarse textured, alkaline soil

Nitrification occurring in an alkaline sandy loam soil fertilized with urea , ammonium sulphate (AS) and ammonium chloride (AC) was studied in the labo ratory at 20 degrees C and 40 degrees C for 30 days. Nitrogen fertilizers w ere applied as nest of sizes 0.2, 0.5, 1.0 and 2.0 g. Unfertilized control and soil mixed with 50 mg N kg(-1) were also included as treatments. Nitrification in all the fertilizer treatments decreased markedly with incr easing nest size. At 20 degrees C, differences among the three N sources we re not significant at 5 days after incubation but marked differences appear ed thereafter. All the N was nitrified by 30 days in case of fertilizers mi xed into the soil. In nest placement, nitrification ranged from 30.1 to 75. 5%, 28.3 to 74.6% and 35.3 to 88.7% for urea, AC and AS, respectively. When equal amounts of fertilizers were placed in a nest, nitrification occurred at a slower rate with urea than with AC and AS. Rates of nitrification wer e significantly higher at 40 degrees C than at 20 degrees C. At 20 days, ni trification from different nest sizes ranged from 8.4 to 64.9% and from 24. 9 to 87.0% at 20 degrees C and 40 degrees C, respectively. The difference i n nitrification at two temperatures were more pronounced at higher nest siz es than at smaller nest sizes. While nitrification with the three N sources decreased linearly with increase in N concentration (nest size) in soil at 40 degrees C, it showed a quadratic relationship at 20 degrees C. At equal N concentration, the highest rate of nitrification occurred with urea and the lowest with AC. At the same rate of applied N (50-2000 mg kg(-1)), AC a nd AS increased electrical conductivity of soil by 1.3-9 times that of urea . Apparent mineral N recovery of applied N decreased with the increase in n est size.