为明确耕作方式对农田土壤全氮及其组分的影响,该文于中国农业大学吴桥实验站展开研究.田间试验布置于2008年,设置翻耕秸秆不还田(PT),翻耕秸秆还田(PTS),免耕秸秆还田(NTS)和旋耕秸秆还田(RTS)4个处理.于2015年冬小麦收获后取样,测定分析了土壤全氮、颗粒氮、矿物结合态氮含量以及土壤全氮储量.研究结果表明,0~5和5~10 cm土层的土壤全氮含量NTS和RTS显著高于PTS,但10~20和20~30 cm土层显著降低(P<0.05).0~50 cm土层的土壤全氮储量秸秆还田各处理间差异不显著,但NTS和PTS较PT分别提高了7.78%和11.09%(P<0.05).在土壤全氮及其组分中,土壤颗粒氮对耕作方式表现出最高的敏感性.0~5 cm土层的土壤颗粒氮含量及其在土壤全氮中的占比NTS和RTS均高于PTS,但在20~30 cm土层均低于PTS(P<0.05).与PT相比,PTS仅提高了0~20 cm土层的土壤全氮和颗粒氮含量,而土壤矿物结合态氮含量没有显著差异,NTS和RTS则同步提高了0~10 cm土层的土壤全氮、颗粒氮及矿物结合态氮含量(P<0.05).综上所述,免耕和旋耕提高了土壤全氮及其组分在表层土壤中的分布,翻耕则在较深土层更具优势,但翻耕阻碍了耕层土壤矿物结合态氮的积累,增加了氮素损失风险.%Growing concerns about environmental conservation and sustainable intensification have raised interests in enhancing soil nitrogen pools. To estimate the effects of different tillage systems on soil nitrogen pools, a field experiment initiated from 2008 with 4 tillage systems (plow tillage without residue retention, PT; plow tillage with residue retention, PTS;no-till with residue retention, NTS; rotary tillage with residue retention, RTS) was conducted in a winter wheat - summer maize double cropping system at China Agricultural Experimental Station in Wuqiao on the North China Plain (NCP). After 7 years of experiment, soil total nitrogen (TN), particulate organic matter nitrogen (POM-N) and mineral-associated organic matter nitrogen (MAOM-N) were determined from 5 soil depths increments. This study observed that concentrations of TN under NTS and RTS were significantly higher than that under PTS in the 0-5 and 5-10 cm soil layers (25.05% and 23.39% higher in the 0-5 cm layer, and 8.16% and 19.60% higher in the 5-10 cm layer, respectively), but trends reversed in the 10-20 and 20-30 cm soil layers (7.72% and 6.66% lower in the 10-20 cm layer, and 26.76% and 27.20% lower in the 20-30 cm layer, respectively). Furthermore, no significant differences in total nitrogen stocks of either 0-30 or 0-50 cm soil layer were observed among tillage treatments with residue retention, but all of them were higher than that of PT treatment. POM-N showed the highest sensitivity among soil total nitrogen and its fractions. Concentration of POM-N under NTS increased by 51.79% in the 0-5 cm topsoil when compared with PTS, but decreased by 18.35% and 53.11% in the 10-20 and 20-30 cm subsoils, respectively. The proportion of POM-N in TN under NTS was also higher than that under PTS in the 0-5 cm layer, but lower in the 5-10 and 20-30 cm layers. Similarly, RTS increased both POM-N concentration and the proportion of POM-N in TN in the 0-5 cm layer when compared with PTS, but decreased the two in the 20-30 cm layer. However, when compared with PT, treatments with residue retention increased both POM-N concentrations and the proportions of POM-N in TN in the upper layers of soil. Concentration of MAOM-N showed a trend similar to TN concentration on the conditions with residue retention. As a result of the accumulation of soil organic materials in the topsoil, NTS and RTS showed relatively higher values of stratification ratio of soil total nitrogen and its fractions as compared with PTS and PT. Compared with PT, NTS and RTS significantly increased concentrations of TN, POM-N and MAOM-N in the 0-10 cm soil layer synchronously. However, PTS only increased TN and POM-N concentrations in the 0-20 cm soil layer compared with PT. In addition, a significantly positive correlation between variation of POM-N and variation of MAOM-N has been observed under NTS and RTS, but not under PTS, when compared with PT. When adopting plow tillage, soil nitrogen increased by residue retention was mainly distributed with the particulate fractions, rarely transferred to the mineral-associated fractions, which might accelerate the depletion of soil nitrogen, and then increase environmental risks.
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