除草剂对土壤氮素循环的影响及其响应机理研究

Herbicide and nitrogen fertilizer were the most important one of pesticides and feitilizers,and which application area and consumption reached over 60 millian hactares and 28 millian tons respectively each year in China. Soil nitrogen was transformed into different forms by soil microbe and enzyme and resulted in its changes in biological effectiveness and loss.However,the herbicides applied to field had a large impact to population and diversity of soil microbes and activity of soil enzymes,that would affct soil nitrogen cycle indirectly.So far,few literatures on the effects of herbicides on soil nitrogen cycle and fate of soil nitrogen were reported in China, and that would influence the accurate estimation of soil nitrogen loss and N2O emission.Therefore,the proposed reseach project will be conducted to determined ammonia volatilization,nitrificaotin-denitrification loss, N2O emission and changes of N forms of farmland soil with herbiciede treatments by intermittend sealing aeration chamber, intact soil column-actylene inhibiton, static closed chamber and agricultural chemistry analysis methods etc respectively in maize-wheat rotaton system in north China; and simultaneously determined the changes of the soil microbes and enzymes which were related to soil nitrogen transformation,and study the effect of herbicides on the target microorganisms by measuring the 15N labeled substrates and products, and assay the relationship between these microbes and enzymes and soil nitrogen cycle. The project reseach rusults will reveal the mechanisms of herbicides how to regulate soil nitrogen transformation by affecting microorganisms, and provide references for estimation of nitrogen fertilizer loss and greenhouse gas N2O emission from farmland systems in China or the global.

除草剂和氮肥是农业上用量最大的农药与化肥品种，我国每年除草剂施用面积0.6亿多公顷，氮肥用量2800多万吨。土壤氮经微生物和酶作用转化成不同形态而影响其生物有效性和损失量，除草剂对微生物种群数量和酶活性影响很大，这必然影响土壤氮循环过程。迄今我国有关除草剂对农田土壤氮循环与去向影响的系统研究尚鲜见报道，不利于氮肥损失和N2O排放等方面的客观评价。项目采用间歇密闭通气法、土柱培养乙炔抑制法、静态密闭箱法和农化分析法，在华北玉米-小麦轮作田间定位下连续测定不同类型除草剂对土壤氨挥发、硝化反硝化损失和N2O排放量及土壤不同形态氮含量动态变化的影响。同时测定与氮转化有关的微生物种群和酶活性变化；通过15N标记的不同底物和产物变化探讨除草剂对靶微生物产生的效应；分析其与氮循环的相关关系。通过宏观和微观上相互印证，揭示除草剂调控氮素转化机理，为我国氮肥损失和温室气体N2O排放估算的环境评价提供依据。

在华北玉米-小麦系统开展了3个轮作周期施用除草剂对土壤氮转化及相关微生物种群变化影响试验。玉米季选用除草剂乙草胺、阿特拉津、百草枯和2、4-D丁酯，小麦季选用骠马、苯磺隆、异丙隆和麦草畏。（1）通气法研究表明，除草剂短时间抑制尿素水解而降低氨挥发，不同除草剂抑制效应有差异，其中２、４-Ｄ丁酯和骠马等效果更好。（2）土柱培养乙炔抑制法研究显示，潮土硝化速率很快，除草剂对其有短暂抑制作用。玉米季反硝化损失高于小麦季(p < 0.01)，除草剂明显抑制反硝化。（3）静态箱法研究显示，除草剂对温室气体排放有减排作用，不同除草剂效果有差异。（4）高通量测序法测定表明，施氮肥减少微生物多样性，不同除草剂对微生物种群数量也有影响。.培养试验表明：除草剂2，4-D减少红壤中细菌和放线菌数量，增加潮土中数量；增加剂量后两种土壤真菌数量均降低(p<0.05)。2，4-D田间用量时激发氨化菌数量，增加用量则抑制氨化菌、硝化菌和反硝化菌。显著抑制自养硝化菌，增加异养硝化菌。对微生物影响与微生物种类、除草剂用量和土壤类型有关。.潮土中尿素氮3d内转化为硝态氮，红壤中30d后转化完成。灭菌接种微生物试验表明，两种土壤接种潮土菌液的硝化速率显著高于接种红壤菌液。红壤pH调至碱性时，接种潮土菌液和红壤菌液其硝化速率显著高于未调节pH红壤。pH和土壤菌液对硝化率均有影响，且二者间存在显著交互作用。高通量测序分析显示，两种土壤之间和不同pH之间微生物的多样性和丰度有差异。.水田改菜地后，土壤细菌、氨化菌、反硝化菌数量显著降低，真菌、放线菌和异养硝化菌变化不大。随着菜地种植年限增加，真菌、细菌、放线菌和异养硝化菌显著增加，氨化菌、亚硝化菌、自养硝化菌和反硝化菌增加不显著。除草剂乙草胺显著抑制3种土壤自养硝化菌和反硝化菌，以及水稻土和30年菜地土氨化菌和异养硝化菌。乙草胺对尿素水解和硝化作用无明显影响，但显著抑制反硝化作用。