双季稻田添加脲酶抑制剂NBPT氮肥的最高减量潜力研究

【目的】添加脲酶抑制剂（Urease inhibitor, UI）是提高肥料利用率的有效途径，在尿素（Urea，U）中添加1%的脲酶抑制剂NBPT（N-丁基硫代磷酰三胺）是目前研究使用证明效果最可靠的添加比例。针对当前稻田氮肥施用水平过高的问题，本文采用田间小区试验研究了目前脲酶抑制剂添加比例下稻田氮肥的减施潜力以及脲酶抑制剂的节肥增效机理。【方法】本试验在我国长江中下游的双季稻田进行，脲酶抑制剂用量NBPT为尿素用量的1%。尿素用量设五个水平为N 90、 112.5、 135、 157.5 和180 kg/hm2，分别依次记为U1、 U2、 U3、 U4和U5， 7个处理为CK（不施氮肥）、 U1+UI、 U2+UI、 U3+UI、 U4+UI、 U5+UI、 U5（U5为传统施氮量， N 180 kg/hm2为农民习惯施氮量），三次重复。U1~U5处理施氮量分别是在农民习惯施氮量的基础上降低50%、 37.5%、 25%、 12.5%、 0%。通过取样分析水稻分蘖期和孕穗期各处理对土壤脲酶活性、 硝酸还原酶活性、 土壤铵态氮含量、 硝态氮含量以及微生物量碳、 氮的含量，研究NBPT对水稻两个主要生育期土壤氮素供应的影响，比较各处理的产量以及氮肥利用率来得出氮肥的减施潜力，在此基础上通过逐步回归分析研究以上各指标对产量的影响，探明脲酶抑制剂（NBPT）在双季稻田的增效机理。【结果】 1) 在双季稻田，添加NBPT后，施氮量为N 135 kg/hm2的籽粒产量达到最高。与传统施氮（单施尿素N 180 kg/hm2）处理相比，早、 晚稻可分别增产8.54%和12.87%，氮肥当季利用率分别提高6.78%和9.46%，可节约氮肥25%； 2)与传统施氮相比，添加NBPT显著降低了水稻分蘖期的土壤脲酶活性和铵态氮含量，显著提高了孕穗期的铵态氮含量，而对此时期的脲酶活性无显著影响，NBPT对两个时期的硝酸还原酶活性、 硝态氮含量及微生物量碳、 氮含量均无明显影响，可见基施的NBPT主要是降低尿素水解速率方面效果显著，并且NBPT具有时效性，其主要是在水稻孕穗期之前起作用，在生态上较为安全； 3) 从各项土壤指标与水稻产量相关性的逐步回归分析结果来看，水稻分蘖期与孕穗期稻田土壤中铵态氮含量对水稻产量影响显著，而且孕穗期的影响大于分蘖期，其余指标则对产量无明显影响。【结论】由于脲酶抑制剂NBPT减缓了分蘖期尿素的水解作用，提高了孕穗期土壤中的铵态氮含量，为水稻后期生长提供充足的氮肥，在双季稻减肥方面具有显著的效果。在本试验土壤条件下，尿素中添加1% 的NBPT，可在提高产量的同时，将传统施氮肥量减少25%，是适于稻田应用的脲酶抑制剂。

Highest potential of subtracting nitrogen fertilizer through addition of urease inhibitor NBPT in double-cropping paddy fields

【Objectives】The addition of urease inhibitor is proved to be an effective measure to improve the efficiency of mineral fertilizer. Addition of urease inhibitor N-(n-butyl) thiophosphoric triamideNBPT］ at a rate of 10 g/kg of urea has been widely used in researches. From the point of the high urea input in present rice production, the highest potential of saving nitrogen fertilizer through adding 1% of NBPT in urea was studied using a field experiment in paddy soils, and the mechanism of saving fertilizer and synergism from urease inhibitor were investigated. 【Methods】A field experiment was conducted in a double-cropping paddy field in middle and lower reaches of the Yangtze River area, Southern China. Urea was mixed with urease inhibitor NBPT at a rate of 10 g/kg urea, five urea levels:  N 90, 112.5, 135, 157.5 and 180 kg/ha were designed and recorded as U1, U2, U3, U4 and U5 in turn, plus a no N control and a normal urea of N 180 kg/ha in the experiment. A completely randomized design with seven treatments and three replicates was as follows,  1) CK (no N control); 2) U1+UI; 3) U2+UI; 4) U3+UI; 5) U4+UI; 6) U5+UI; 7) U5. The subtracting ratio of N fertilizer for U1, U2, U3, U4 and U5 is 50%, 37.5%, 25%, 12.5% and 0% respectively. The activities of urease and nitrate reductase, the contents of NH⁺₄-N, NO^-₃-N and microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) in soil were analyzed in tillering and booting stages. The rice yield and N efficiency were investigated. 【Results】1) With the addition of UI, the highest yield was obtained at N rate of 135 kg/ha. Compared with the normal urea N rate of 180 kg/ha, the grain yields were increased by 8.54% and 12.87% in early and late rice, the recovery of applied N improved by 6.78% and 9.46%, respectively, and 25% of N fertilizer could be saved as a result. 2)The addition of NBPT in urea notably reduced urease activity, and soil NH⁺₄-N content at the tillering stage and increased soil NH⁺₄-N content at the booting stage, while there were no obvious effects on nitrate reductase activity (NRA), soil NO^-₃-N content and MBC and MBN. There was no significant difference in urease activity between with and without NBPT at the booting stage. Therefore, the urease inhibitor NBPT was effective before the booting stage and had less long term negative influence on soil environment. 3)The stepwise regression analysis reveals that the grain yield of rice is significantly associated with NH⁺₄-N content in soil at the tillering and booting stages, especially, the latter. However, other properties in soil have no obvious effects on the grain yield. 【Conclusions】The potential of saving N fertilizer from NBPT is outstanding in double-cropping paddy fields. Compared with the normal urea, N fertilizer is saved by 25% when NBPT is used. NBPT slows down the hydrolytic action of urea and dramatically improves soil NH⁺₄-N content in the booting stage, which appears to be the dominant factor of saving N fertilizer. The above results suggest that NBPT could remain adequate N resources at late growth stage for rice and serve as a urease inhibitor for developing slow release fertilizer in paddy soils.Objectives] The addition of urease inhibitor is proved to be an effective measure to improve the efficiency of mineral fertilizer. Addition of urease inhibitor N–(n-butyl) thiophosphoric triamide NBPT] at a rate of 10 g/kg of urea has been widely used in researches. From the point of the high urea input in present rice production, the highest potential of saving nitrogen fertilizer through adding 1% of NBPT in urea was studied using a field experiment in paddy soils, and the mechanism of saving fertilizer and synergism from urease inhibitor were investigated. Methods: A field experiment was conducted in a double-cropping paddy field in middle and lower reaches of the Yangtze River area, Southern China. Urea was mixed with urease inhibitor N–(n-butyl) thiophosphoric triamide NBPT] at a rate of 10 g/kg urea, five urea levels: 90, 112.5, 135, 157.5 and 180 kgN/ha were designed and recorded as U1, U2, U3, U4 and U5 in turn, plus a no N control and a normal urea of 180 kg N/ha in the experiment. A completely randomized design with seven treatments and three replicates was as follows: 1) CK (no N control), 2) U1+UI, 3) U2+UI, 4) U3+UI, 5) U4+UI, 6) U5+UI, 7) U5. The subtracting ratio of N fertilizer for U1, U2, U3, U4 and U5 is 50%, 37.5%, 25%, 12.5% and 0% in turn. The activities of urease and nitrate reductase, the contents of NH⁺₄-N, NO^-₃-N  and microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) in soil were analyzed in tillering and booting stages.. The rice yield and N efficiency were investigated. Results] (1) With the addition of UI, the highest yield was obtained at N rate of 135 kgN/ha. Compared with the normal urea rate of 180 kg N/ha, the grain yields are increased by 8.54% and12.87% in early and late rice, the recovery of applied N improved by 6.78% and 9.46%, respectively, and 25% of N fertilizer can be saved as a result. (2)The addition of NBPT in urea notably reduces urease activity , and soil NH⁺₄-N content at the tillering stage and increases soil NH4+-N content at the booting stage, while there are no obvious effects on nitrate reductase activity (NRA), soil NO^-₃-N content and microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN). There is no significant difference of urease activity between urea with and without NBPT at the booting stage. Therefore, the urease inhibitor NBPT is effective before the booting stage and has less long term negative influence on soil environment. (3)The stepwise regression analysis reveals that the grain yield of rice is significantly associated with NH⁺₄-N content in soil at the tillering and booting stages, especially, the latter. However, other properties in soil have no obvious effects on the grain yield.