Effect Of Urease Inhibitor LIMUS On Ammonia Mitigation And Crop Yield And Nitrogen Use Efficiency In Different Croplands Of China

Urea is a main chemical nitrogen (N) fertilizer in China, accounting for more than50%of total N fertilizer consumption. Urea plays an important role in food security; while overuse of N fertilizer can also cause lower N use efficiency (NUE, averaged35%) and numerous environmental problems in China. Ammonia (NH3) volatilization is a significant N loss pathway for urea, which is often more than30%of applied N in calcareous and alkaline soils. Thus it is very significant to decrease NH3loss in order to achieve a higher NUE and to increase grain yields. The use of a urease inhibitorwould be an appropriate measure to achieve these goals, as it could inhibit urease activity and thereby delay the hydrolysis of urea and reduce the potential for NH3loss. A new urease inhibitor LIMUS (Limus(?)) was developed by the BASF SE, Germany, which was modified on the basis of N-(n-butyl) thiophosphoric triamide (NBPT). Currently no systematic study has been conducted to identify the effect of LIMUS on reducing NH3loss and increasing NUE and crop yields in China. Therefore this paper dealed with LIMUS impacts on winter wheat (3field experiments at Xiping (XP), Quzhou (QZ) and Yangling (YL) sites) and maize (3field experiments at Shangzhuang (SZ), QZ and Lishu (LS) sites) and37arable soils across China through comparing plain urea and urea amended with LIMUS treatments. NH3loss alone or NH3loss together with NUE, crop yields, and apparent N balance in all treatments were evaluated to investigate the effects of LIMUS either in lab or field conditions. The main results were summarized as follows:(1) Using the calibrated Drager-Tube Method (DTM), I found cumulative NH3losses after two weeks for conventional urea treatment (Ncon) were10～25%of applied N while those for urea amended with LIMUS (Nopt/L-1, Nopt/L-2) were only0～6%of applied N during winter wheat growing season. The cumulative NH3losses for Ncon were3～57%of applied N while NH3losses for urea amended with LIMUS were0～26%of applied N during maize growing season. The results proved the high potential of LIMUS for substantially mitigating65%to100%of NH3loss across all field experiment sites.(2) Crop yields were not significantly different between optimized N treatmnts with (Nopt/L1, Nopt/L2) or without (Nopt-1, Nopt-2) LIMUS compared with Neon at any winter-wheat or maize experimental sites. However, a clear11～23%increase in apparent nitrogen recovery (REN) with LIMUS resulted at the QZ site, with an increase in REN up to65～76%under a further20%N-reduced urea plus LIMUS treatment (N80%opt/L). Whether or not a beneficial effect on crop yield was realized mainly depends on initial indigenous soil N status and the amount of NH3loss.(3) Estimated apparent N balance also demonstrated that farmer’s conventional urea-N fertilization at all sites had no positive effect on grain yield compared to the optimized treatments (with lower N rates), but led to significantly high residual NO3-N with average120～170kg N ha-1and apparent N loss by100～120kg N ha-1, including one third of which lost as NH3volatilization (30～40kg N ha-1). The rest two thirds of N loss may be lost due to N leaching and/or nitrification/denitrification. Our results reveal an N saving potential in farmer’s conventional N rate by38～44%for wheat and 25～50%for maize in major croplands of China without yield loss but significant less N loss to the environment.(4) Controlled lab experiments were conducted for investigating efficiency of LIMUS in reducing NH3loss from surface applied urea on different soils in China and Germany. In one lab experiment, most of37Chinese arable soils (e.g., neutral and calcareous soils) had high potential of NH3loss for surface applied urea, while the presence of LIMUS decreased NH3loss significantly through delaying urea hydrolysis in all37arable soils. Another lab experiment was conducted to check the concentration effect of two urease inhibitors (NBPT and LIMUS) on reduction of NH3loss from the German Lihof soil and Chinese Shuangzhuang also Quzhou soils. The LIMUS had better effect on reduction of NH3loss compared with the NBPT, especially under lower concentration levels.