轮作模式和氮肥处理对稻田土壤有机碳储量及其结构的影响

Effects of Crop Rotation Patterns and Nitrogen Fertilizer Levels on Storage and Structure of Soil Organic Carbon in Paddy Fields

【目的】探讨不同水旱轮作模式与水稻季施氮水平在稻田土壤固碳(有机碳储量及其官能团特征)中的作用。【方法】依托中国水稻研究所水-旱轮作长期定位试验(2003年至今),研究4种轮作模式[水稻-冬闲(RF)、水稻-紫云英(RC)、水稻-小麦(RW)和水稻-稻草覆盖种植马铃薯(RP)]与2个水稻季氮肥处理[不施氮(N0,0kg/hm^(2))和正常施氮(N1,135kg/hm^(2))]对稻田土壤有机碳储量(0-50cm)和有机碳官能团特征(0-20cm)的影响。【结果】1)在土壤浅耕层(0-20 cm)内,轮作能够在一定程度上提高有机碳含量,表现为RP>RC>RW或RF;但对于全耕层(0-50、0-40和0-30cm)土壤有机碳储量而言,冬作(RP,RC和RW)与冬闲(RF)无显著差异,而施氮更有利于土壤固碳。2)水稻季不施氮处理下:相较于RF,冬作模式显著增加包括烷基碳和芳香碳在内的难降解组分,而抑制以烷氧碳为主的易降解组分,明显提高了土壤腐殖化指数、芳香性和疏水性,助力浅层土壤(0-20 cm)总有机碳储备的增加。其中,腐殖化指数和疏水性与还田秸秆C/N比值关系密切,这在浅层土壤固碳上具有重要意义。【结论】相较于轮作,适度施氮对全层土壤有机碳储备更有意义;而周年水旱轮作中全量秸秆还田对土壤有机质积累的效应仅停留在浅耕层,对全土层土壤有机碳储备的作用则被高估。秸秆碳在稻田的去向还有待进一步探索。

【Objective】The aim of this study is to clarify the role of paddy-upland crop rotation patterns and nitrogen fertilizer levels in carbon sequestration(organic carbon storage and chemical functional group characteristics)in paddy soils.【Method】Relying on the long-term paddy-upland crop rotation experiments in the China National Rice Research Institute(2003 to present),we investigated the effects of four paddy-upland crop rotation patterns:rice-fallow(RF),rice-green manure(Chinese milk vetch;RC),rice-wheat(RW),and rice-potato with rice straw mulch(RP)at two nitrogen levels during the rice growing season:no nitrogen application(N0,0 kg/hm^(2))and normal nitrogen application(N1,135 kg/hm^(2))on soil organic carbon stocks(0-50 cm)and the characteristics of soil organic carbon functional groups(0-20 cm)in paddy fields.【Result】1)Within the shallow tillage layer(0-20 cm)of the soil,crop rotation was able to enhance soil organic carbon content to some extent,with the order of effectiveness being RP>RC>RW or RF.However,for soil organic carbon stocks in the full tillage layer(0-50,0-40,and 0-30 cm),there were no significant differences between the winter crop rotations(RP,RC,and RW)and RF.In contrast,nitrogen application was found to be more favorable for soil carbon sequestration.2)In the N0 treatment during the rice growing season after winter cropping,compared to RF,winter crop rotations(RP,RC,and RW)significantly increased the stable forms of carbon,including Alkyl C and Aromatic C,while suppressing the labile form of carbon dominated by O-Alkyl C.This treatment also significantly increased the soil humification index(HI),aromaticity(fa),and hydrophobicity,contributing to an increase in total soil organic carbon reserves in the surface layer(0-20 cm).It is noteworthy that the HI and hydrophobicity are closely associated with the C/N ratio of returned straw,which is important for promoting soil carbon sequestration in shallow soils.【Conclusion】In comparison to crop rotation,moderate nitrogen application has shown to be more favorable for soil organic carbon reserves throughout the soil profile.On the other hand,the impact of full straw return on soil organic matter accumulation in the annual upland-paddy rotation was primarily observed in the shallow tillage layer,indicating that the effect of straw return on soil organic carbon accumulation might be overestimated when considering the entire soil profile.Therefore,further exploration is needed to better understand the fate and destination of straw carbon in paddy fields.