秸秆粉碎和焚烧还田对石灰性紫色土耕层土壤孔隙和有机碳的影响

Effects of shredded straw and burned straw returning to the field on soil porosity and organic carbon in cultivated layer of calcareous purple soil

为明确川中丘陵区长期不同秸秆还田方式对石灰性紫色土耕层土壤孔隙及有机碳的影响,利用田间原位监测和计算机断层扫描技术,测定夏玉米-冬小麦轮作、秸秆不还田(RMW0),夏玉米-冬小麦轮作、秸秆50%粉碎还田(RMWshred)和夏玉米-冬小麦轮作、秸秆50%焚烧还田(RMWburn)处理耕层土壤有机碳浓度、储量及孔隙特征参数。结果表明:RMWshred和RMWburn均能显著增加耕层土壤总孔隙度、降低土壤容重,RMWburn耕层土壤大孔隙度是RMWshred的2.7倍。RMWshred和RMWburn较RMW0能有效改善土壤大孔隙集中分布现象,使层间大孔隙分布更均匀,3个处理孔隙数量均以当量孔径100~500μm孔隙为主,RMWshred和RMWburn优化了耕层土壤不同当量孔径孔隙数量比和体积比,且以RMWshred更优。RMWburn有利于增加耕层土壤>1 000μm孔径的孔隙数量,RMWshred耕层土壤>1 000μm孔径的孔隙平均直径趋小。RMWshred和RMWburn平均喉道截面积、平均喉道截面形状因子、平均孔隙形状因子均较RMW0低,长期秸秆还田使耕层土壤孔隙向有利于保水保肥的方向转变,且RMWshred保水保肥能力较RMWburn更优。秸秆连续还田15 a后,只有RMWshred耕层土壤有机碳浓度增幅显著。综合比较两种还田方式在改善川中丘陵区石灰性紫色土耕层土壤孔隙特征和固碳效果的差异表明,长期秸秆粉碎还田较焚烧还田更有利于改善耕层土壤孔隙特征,更能有效积累耕层土壤有机碳,更有利于川中丘陵区农业绿色发展。

To clarify the effects of different long-term straw-returning methods on soil pores and organic carbon in the cultivated layer of calcareous purple soil in the hilly area of the central Sichuan Basin, in-situ monitoring and computed tomography were used to determine the organic carbon concentration and storage, and pore characteristics of soil in the cultivated layer of the following treatments:RMW0(summer maize-winter wheat rotation, without straw returned to the field), RMWshred(summer maize-winter wheat rotation, 50% straw shredded and returned to the field), and RMWburn(summer maize-winter wheat-straw rotation, 50% straw burned and returned to the field). The results showed that the total porosity of cultivated layer soil was significantly increased by both the RMWshred and RMWburn treatments, while the corresponding bulk densities were decreased. The macroporosity of cultivated layer soil in RMWburn was 2.7 times higher than that of RMWshred. Compared with RMW0, the RMWshred and RMWburn treatments could effectively improve the centralized distribution of soil macropores and make the distribution of interlayer macropores more uniform. The quantities of pores in all three treatments were dominated by equivalent pore diameters of 100~500 μm. The RMWshred and RMWburn treatments optimized the pore number ratio and volume ratio of different equivalent pore diameters in the cultivated layer of soil, with the RMWshred treatment having a superior effect. RMWburn was beneficial for increasing the number of >1 000 μm equivalent pores in the cultivated layer of soil, while the average diameter of >1 000 μm pores in the cultivated layer of soil under the RMWshred tended to be smaller. The mean throat cross-sectional area,mean throat cross-sectional shape factor and mean pore shape factor of RMWshred and RMWburn were lower than those of RMW0. Long-term straw returning to the field caused the pore space of the cultivated soil to change in a direction favorable for water and fertilizer retention,and the water and fertilizer retention ability of RMWshred was better than that of RMWburn. After 15 years of continuous straw returning, the soil organic carbon concentration only increased significantly in the RMWshred treatment. Based on a comprehensive comparison of the differences between the two straw-returning treatments, in terms of improving pore characteristics and carbon sequestration in the cultivated soil layer in the hilly area of the central Sichuan Basin, long-term returning of shredded straw is more conducive to improving soil pore characteristics and more effective in accumulating soil organic carbon than long-term returning of burned straw, making it more sustainable option for the green development of agriculture in the hilly area of the central Sichuan Basin.