旱地土壤有机碳氮和供氮能力对长期不同氮肥用量的响应

【目的】揭示旱地土壤有机碳氮、氮素矿化对长期不同氮肥用量的响应及有机碳氮与氮素矿化的关系,进而评价土壤供氮能力,为旱地土壤氮素管理提供参考。【方法】在陕西杨凌2004年开始的旱地小麦氮肥长期定位试验基础上,采集不同氮肥用量(0(N0)、160(N160)、320(N320)kg N·hm~(-2))试验的土壤样品,测定土壤有机碳、有机氮,微生物量碳、氮含量,并采用间歇淋洗好气培养法测定土壤的氮素矿化。【结果】与对照N0相比,施用氮肥(N160、N320)增加了0—10、10—20、20—40、0—40 cm土层有机碳含量,且在小麦播前期和收获期表现不一致;施氮(N160和N320)处理均显著提高了0—10 cm土层有机氮含量,但仅N320处理显著提高了0—40 cm土层土壤有机氮含量;施用氮肥(N160、N320)未改变0—10、10—20 cm土层土壤微生物量氮和微生物量碳含量,仅N320处理显著提高了20—40、0—40 cm土层微生物量氮和微生物量碳含量。0—10 cm土层,土壤氮素矿化量、矿化势(N_0)与施氮量、有机氮含量呈显著正相关,氮素矿化速率常数(k)则与其呈显著负相关。10—20 cm土层,施氮处理(N160、N320)土壤的氮素矿化量均显著高于不施氮处理(N0),增幅分别为27.3%和35.2%,且与施氮量、有机碳、有机氮含量呈显著正相关;氮素矿化势(N_0)随着有机碳增加而显著增加,矿化速率常数(k)则降低。20—40 cm土层,N320能提高氮素矿化量,并与有机氮、微生物量碳呈显著正相关。【结论】合理施氮肥能明显促进旱地0—10和10—20 cm土壤有机碳、有机氮积累,提高土壤氮素矿化能力,降低氮素矿化速率,是提高旱地土壤有机氮、有机碳含量和土壤供氮能力的有效途径。

Responses of Soil Organic Carbon,Organic Nitrogen and Nitrogen Supply Capacity to Long-Term Nitrogen Fertilization Practices in Dryland Soil

【Objective】The purpose of this study is to reveal the response of soil organic carbon, organic nitrogen and soil N mineralization to different N application rates and their relationships, and then to evaluate soil N supply capacity in dryland soil. 【Method】A ten-year-old winter wheat (Triticum aestivum L.) field experiment with N application rates (0 (N0), 160 (N160) and 320 (N320) kg·hm^-2, plus 100 kg P₂O₅·hm^-2) in the experiment farm of Northwest A&F University, Yangling, Shaanxi Province was conducted to determine soil organic carbon (SOC), N (SON), microbial biomass C (MBC) and biomass N (MBN) and a laboratory incubation method was used to determine the capacity of soil nitrogen (N) mineralization. 【Result】Compared with N0 treatment, N fertilization treatments (N160 and N320) significantly increased SOC at 0-10, 10-20, 20-40 and 0-40 cm soil depths, and they had different effects in the stages of wheat pre-sowing and harvest; N160 and N320 treatments also significantly increased SON at 0-10 cm soil depth, and N320 treatment only increased SON at 0-40 cm soil depth; N fertilization treatments (N160 and N320) did not change MBN and MBC concentrations at 0-10 and 10-20 cm depths, while N320 treatment significantly increased MBN concentrations at 20-40 and 0-40 cm depths. In 0-10 cm soil depth, the amount of cumulative mineralized N and potentially mineralizable N (N₀) had a significant positive correlation with N fertilizer rates and SON, while N mineralization rate constant (k) had a negative correlation with them. In 10-20 cm soil depth, during the whole incubation process, the amount of cumulative mineralized N in different N treatments was significantly higher than that in N0 treatment, with the increment of 27.3% (N160) and 35.2% (N320), respectively, and there was a significant positive correlation between cumulative mineralized N and SON, SOC as well as N rates. The potentially mineralizable N (N₀) significantly increased with the increment of N fertilizer application rate, while the N mineralization rate constant (k) decreased. In 20-40 cm soil depth, the amount of cumulative mineralized N increased with the treatment of N320 and had a significant positive correlation with soil MBC and SON. 【Conclusion】Applying a reasonable rate of N fertilizer is one of the effective practices to improve the soil organic N and organic C concentrations in the dryland of Loess Plateau, and can also increase the soil potentially mineralizable N, reduce the N mineralization rate, thus improve soil N supply capacity.