不同施肥措施对晋南旱塬麦田土壤碳氮变化的影响

Effect of Different Fertilizations Patterns on Soil Carbon and Nitrogen Changes of Dryland Wheat Field in Southern Shanxi of China

【目的】明确不同施肥措施下麦田土壤碳氮库的变化情况,为旱地小麦化肥定量减施及土壤肥力提升提供依据。【方法】于2012―2017年在晋南黄土旱塬冬小麦种植区,设置农户施肥(FF)、监控施肥(MF)和不施肥(NF)3种施肥处理,研究了连续5 a不同施肥措施对旱地麦田耕层土壤总有机碳氮、有机碳氮组分及0～200 cm土层土壤硝态氮累积量的影响。【结果】晋南黄土旱塬麦田,在秸秆还田基础上,连续5 a不施肥(NF)耕层土壤总有机碳较2012年试验前提高了24.7%,而单施化肥处理(FF、MF)下土壤总有机碳下降了2.4%～8.2%。连续单施化肥较不施肥显著提高了可溶性有机碳、轻组有机碳以及可溶性有机氮质量分数,其中传统农户施肥对土壤可溶性有机碳的贡献率显著高于监控施肥处理的。不同施肥处理土壤轻组有机碳在总有机碳中的分配比例为17.9%～31.3%;不施肥处理较单施化肥处理有利于维持较高的土壤重组有机碳量,利于土壤有机碳的固存。不同施肥处理对轻组有机氮和重组有机氮均没有显著影响。传统农户施肥处理0～200 cm土层硝态氮累积量高达426.0 kg/hm^2,且67%集中在100～200 cm土层,具有淋失风险。而监控平衡施肥在累计氮肥投入量减少36.9%基础上,0～200 cm土层硝态氮残留量较农户施肥低51.4%。【结论】黄土旱塬麦区,由于前期农户过量施氮,不施肥种植结合秸秆还田可提高土壤总有机碳量,主要增加了矿物紧密结合态的重组态有机碳量。单施化肥则促进了土壤有机质的矿化分解,提高了土壤中活性有机碳氮量。传统农户施肥模式促使0～200 cm土层产生大量硝态氮残留,具有较高淋失风险。

[Objective] The objective of the study is to determine the changes of soil carbon and nitrogen under different fertilizations, and to provide the theoretical support for reducing chemical fertilizer application rate and improving soil fertility in the rainfed winter wheat system. [Method] The study was carried out with three fertilization treatments, including the farmer fertilization （FF）, the monitoring fertilization （MF） and no fertilization （NF）, during 2012-2017 in the winter wheat cropping region of dry highland in Southern Shanxi. The changes of soil total organic carbon （TOC） and nitrogen （TON）, organic carbon and nitrogen fractions, and soil nitrate-N residue in the 0~200 cm soil profile were assessed. [Result] Soil TOC concentration under NF treatment in 2017 increased by 24.7% compared to that in 2012, which under FF and MF treatments decreased by 2.4%-8.2%. Continuous chemical fertilizer application was more beneficial to the increase of soluble organic carbon （SOC）, soluble organic nitrogen （SON）, and light fraction organic carbon （LFOC） compared to NF treatment, in addition, the effect of MF treatment on the increase of SOC was larger than that of FF treatment. The proportion of LFOC in the TOC under different treatments ranged from 17.9% to 31.3%, therefore, heavy fraction organic carbon （HFOC） was considered to be the main form of soil organic carbon sequestration in the wheat field. Compared to the FF and MF treatments, the NF treatment significantly increased the HFOC concentration, which was favor- able for soil organic carbon sequestration. However, no significant difference in both light fraction organic nitro- gen （LFON） and heavy fraction organic nitrogen （HFON） were observed among different fertilization treatments. The accumulation amounts of nitrate nitrogen in 0-200 cm soil layer under the FF treatment had been up to 426.0 kg/hm2, 67% of nitrate nitrogen concentrated on the 100-200 cm soil profile with a strong leaching risk. In contrast, soil nitrate-N residue in 0-200 cm soil profile under the MF treatment reduced by 51.4% compared to that under the FF treatment, meanwhile, the rate of nitrogen application under the of FF treatment also decreased by 36.9%. [Conclusion] Based on excessive nitrogen application before the experiment began, no fertilization along with straw returning increased the HFOC concentration in rainfed winter wheat cropping region on the Loess Plateau. Single chemical fertilizer applications could facilitate the decomposition of soil organic matter, resulting in an increasing of labile organic carbon and nitrogen fractions. A large amount of nitrate-N residue was observed in the 0-200 cm soil profile under traditional farmer fertilization with a potential leaching risk.