小麦玉米轮作体系农田土壤有机氮组分对施氮量的响应

【目的】土壤有机氮组成和有效性影响土壤肥力的高低。研究不同施氮量下土壤有机氮组分含量的变化规律，及其与冬小麦氮素吸收之间的关系，为科学开展氮肥减施提供理论依据。【方法】冬小麦–夏玉米轮作田间试验在河南温县进行，试验历经3季冬小麦和两季夏玉米。小麦设置5个施氮(N)量处理：300 kg/hm²(N300)、225 kg/hm² (N225)、195 kg/hm² (N195)、165 kg/hm² (N165)、0 kg/hm² (N0)，从第2季冬小麦开始，调查冬小麦产量和吸氮量，小麦播种前和收获后测定0—20 cm土层土壤全氮、有机氮组分含量。【结果】实现冬小麦稳产的最低施氮量为165 kg/hm²，满足冬小麦对氮素需求的最低施氮量为195 kg/hm²。酸解氮(TNex)是土壤中主要的有机氮组分，占全氮的59.06%～92.26%。随着试验时间的延长，N165和N195处理降低了TNex在有机氮中的比例，而N0、N225和N300...

Response of soil organic nitrogen components to nitrogen application rate in a wheat-maize rotation cropland

  【Objectives】  The composition and availability of soil organic nitrogen (SON) play key roles in soil N retention and supply. Studying the effects of N fertilizer application rate on soil organic N components could provide a reference for rational management of N fertilizer.  【Methods】  A field experiment was conducted in Wenxian, Henan Province, and lasted for three winter wheat seasons and two summer maize seasons. The N fertilizer application rates on wheat were 300 kg/hm2 (N300), 225 kg/hm2 (N225), 195 kg/hm2 (N195), 165 kg/hm2 (N165), and 0 kg/hm2 (N0). Wheat yield and N uptake were investigated. Before sowing and after wheat harvest, soil samples were collected to determine total N and organic N content.   【Results】  The minimum N application rate (N165) recorded a stable yield while N195 met the N demand of winter wheat. Acid-soluble nitrogen (TNex) is the main component of SON, accounting for 59.06%?92.26% of total N. TNex was composed of three components, amino sugar nitrogen (ASN), ammonium nitrogen (ANN), and amino acid nitrogen (AAN), which accounted for 18.40%?46.62%, 8.91%?34.40%, and 13.43%?28.52% of TNex, respectively. The reduction of the N application rate led to an increase and decrease in ANN and ASN contents. The results of redundancy analysis indicated the relationship among soil organic N components and ASN before sowing, ANN before sowing, AAN before sowing, and N fertilizer applying rate. Their proportional contribution to the variation in SON was 19.11%, 18.19%, 9.80%, and 17.45%, respectively. The results of the structural equation analysis indicated that the N fertilizer application rate affected the transformation relationship among SON components and their contribution to soil N supply. Under medium and low N application rates, AAN was the key component of soil N supply. The contribution of AAN to the N uptake of winter wheat was 19.11%. ASN was the key component of soil N supply under a high N application rate, and the contribution of ASN to N uptake of winter wheat was 8.65%.   【Conclusions】  Acid-soluble N is the main organic N component in Wenxian soil. N application rate affects soil organic N component contents and transformation relationship. Low N application rates decrease soil total N, reducing the proportion of acid-soluble nitrogen. High N application rates can maintain the stability of acid-soluble N. Among the acid-soluble N, low N application rates increase the proportion of ANN and decrease the proportion of ASN. Under medium and low N application rates, AAN is the key component of soil N supply. Under high N application rates, ASN is the key component of soil N supply.