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Nitrogen dynamics and budgets in a clay loam soil (Meadow Aqualf) in the North China Plain were investigated in a winter wheat (Triticum aestivum L.) and maize (Zea mays L.) cropping system comparing the effects of four N rates (0, 120, 240 and 360 kg N ha−1 as urea) applied twice to each crop over 2 years. Ammonium nitrogen (NH4-N) in the soil profile remained at a low and constant level (except in the surface 20 cm layer) following application of fertilizer N. In contrast, nitrate nitrogen (NO3-N) levels were significantly altered by the rate of applied N. A strong tendency of NO3-N to move from the surface layer to the lower layers (20–100 cm) was observed during the wheat and maize growth seasons in treatments of 240 and 360 kg N ha−1 per crop (N240 and N360). The amounts of NO3-N accumulated in the soil profile were significantly higher in N240 and N360 than those in N0 and N120 (treatments receiving 0 and 120 kg N ha−1 per crop). After 2 years, soil NO3-N levels at 0–300 cm depth in N120, N240 and N360 amounted to 336, 815 and 1141 kg ha−1, respectively, with more than half of these amounts distributed in the 100–300 cm layer. The calculated total N balance indicates that most fertilizer N was available as NO3-N in the top 300 cm of the soil profile using traditional fertilization and irrigation practices. Over the subsequent 2 years, N losses were calculated to be relatively low in N120 but significantly higher in N240 and N360. Measured gaseous N losses showed that NH3 volatilization and denitrification comprised only a small fraction of total N losses during the 2-year rotation, while NO3-N leaching from the top 100 cm of the soil profile accounted for most N losses across all N rates and experimental years. The N budget showed that accumulation and/or leaching of NO3-N below 100 cm depth (beyond the reach of most roots) was the main pathway for N losses in the winter wheat–maize cropping system. The recommended N application rate of 120 kg N ha−1 minimized soil NO3-N accumulation and leaching losses while maintaining high yields and N utilization by winter wheat and maize. [Copyright &y& Elsevier]

Field experiments were conducted at three typical wheat–maize double-cropping sites in north and northwest China to investigate ammonia (NH 3 ) volatilization from urea and from urea amended with 0.12% (w/w) Limus ® (a new urease inhibitor consisting of 75% N-(n-butyl) thiophosphoric triamide (NBPT) and 25% N-(n-propyl) thiophosphoric triamide (NPPT)) in winter wheat. Grain yields and nitrogen (N) budgets of all N treatments were also evaluated to investigate the effects of urea-N application rates and Limus during one wheat season. Cumulative NH 3 losses after two weeks for conventional urea were 11–25% of applied N, while those for urea amended with Limus were only 0–6% of applied N. The urease inhibitor increased fertilizer N retention more strongly when soil and environmental conditions promoted extensive NH 3 losses. However, grain yields were not significantly ( P > 0.05) enhanced by Limus compared to conventional urea at all three sites. A clear increase in apparent N recovery efficiency (RE N ) with Limus (ranging from 10 to 16%) resulted at the Quzhou (QZ) site compared to equal amounts of optimized urea-N, with an increase in RE N of up to 65% under a further 20% N-reduced urea amended with Limus treatment. The study also demonstrated the urgency of appropriate fertilizer N management in China. [ABSTRACT FROM AUTHOR]