氮肥减施和秸秆还田对土壤固定态铵含量的影响

Effects of Fertilizer Nitrogen Reduction and Crop Residue Return on Soil Fixed Ammonium Content

【目的】固定态铵作为土壤氮素的暂存库,其含量的变化能够影响土壤的保氮供氮功能,而深入探究氮肥减施对土壤固定态铵的影响及其对秸秆还田的响应,可为优化农田氮肥管理提供理论依据。【方法】依托位于中国东北黑土区玉米种植系统连续9年全量玉米秸秆覆盖归还的保护性耕作试验平台,通过设置玉米秸秆不还田(S0)、秸秆还田量33%(S33)和秸秆全量覆盖还田(S100)3个秸秆还田量处理,以及240 kg hm^(−2)(N240)、190 kg hm^(−2)(N190)、135 kg hm^(−2)(N135)、0 kg hm^(−2)(N0)4个氮素施用水平,研究氮素减施3年后土壤固定态铵总量的变化以及不同秸秆还田量对固定态铵的影响。【结果】秸秆不还田时,土壤固定态铵总量随施氮量降低而逐渐下降,且在不施氮肥处理(N0)时显著低于施氮肥处理;在S33N190时土壤-作物系统出现氮素缺乏,并且随施氮量的下降土壤固定态铵降低量与氮素缺乏量之间具有显著的正相关关系。在所有氮肥水平,秸秆还田尤其是全量秸秆还田均有利于缓解固定态铵的释放,但在N135处理时秸秆效应较弱。整体上,与对照相比,S100N190处理土壤固定态铵的降低量最小。另外,秸秆还田降低了施肥处理土壤硝态氮含量。【结论】在氮肥减施条件下,土壤固定态铵可以释放供氮,氮肥减施20%配合免耕全量秸秆覆盖还田可在保持土壤固定态铵库相对稳定的基础上,维持土壤-作物系统的氮素平衡。

[Objective]Soil fixed ammonium(NH_(4)^(+)),as a temporary pool of nitrogen(N),the change of its content can affect the function of soil N retention and supply.The response mechanisms of soil fixed NH_(4)^(+)and crop residue return to N fertilizer reduction should be investigated,in order to provide theoretical basis for optimizing N fertilizer management in agroecosystems.[Method]Based on the experimental platform of conservation tillage corn planting system with full crop residue return(9 years)in the black soil region of Northeast China,a fertilizer reduction experiments were set up with:3 crop residue return treatments,0(S0),33%(S33)and 100%(S100);4 N fertilizer application rates,240 kg hm^(−2)(N240),190 kg hm^(−2)(N190),135 kg hm^(−2)(N135),and 0 kg hm^(−2)(N0).[Result]When the crop residue removal,the total amount of fixed NH_(4)^(+)gradually decreased with the decrease of N application and was significantly lower than that of the fertilization treatment in the N0 treatment.N deficiency appeared in the soilcrop system at S33N190,and the fixed NH_(4)^(+)decreased with the decrease of N application.There was a significant positive correlation between fixed NH_(4)^(+)reduction and N deficiency.At all N fertilizer levels,crop residue return,especially full crop residue return,was beneficial to alleviating the release of fixed NH_(4)^(+),but the crop residue effect was weaker under N135 treatment.Overall,the S100N190 treatment showed the smallest reduction in fixed NH_(4)^(+)compared to the control.In addition,crop residue return reduced the nitrate N content in the fertilization treatment.[Conclusion]Under the condition of reducing N fertilizer application,fixed NH_(4)^(+)can release and maintain N supply,reducing N fertilizer application by 20%with no-tillage and full crop residue return can maintain the N supply and balance in the soil-crop system.