免耕对土壤团聚体特征以及有机碳储量的影响

以实施7年的中国科学院禹城综合试验站冬小麦夏玉米轮作免耕长期定位试验场为对象,研究免耕条件下土壤水稳性团聚体和有机碳储量的变化,为进一步评价免耕措施对黄淮海平原土壤结构和质量的影响提供科学依据。设置免耕(NT)、免耕秸秆不还田(NTRR)、常规耕作(CT)3种处理,分析土壤表层(0~20 cm)及深层(20~60 cm)水稳性团聚体分布特征、土壤有机碳以及团聚体有机碳的变化和相互关系。研究结果表明:由于减少了对土壤的破坏以及增加了秸秆还田和有机肥的施用,与常规耕作相比,NT和NTRR可提高表层土壤有机碳含量和储量、水稳性团聚体平均重量直径(MWD)和几何平均直径(GMD),以及大团聚体有机碳的含量和储量。其中,秸秆覆盖比施用有机肥对表层土壤有机碳储量和0.25~2 mm团聚体有机碳储量的提高具有更显著的作用。与表层不同,深层土壤有机碳和大团聚体有机碳的含量和储量表现为NT

Effect of no-tillage on soil aggregate and organic carbon storage

No-tillage(NT) is an increasingly agronomic practice in China.Tillage practices deeply affect soil quality and organic carbon(SOC) accumulation.The effect of NT,as a form of conservation tillage,on soil organic carbon storage had remained highly contentious.To shed further view on the effect of NT on soil structure and quality in the Huang-Huai-Hai Plain(HP),a long-term no-tillage experimental site for the main crop rotation-winter wheat(Triticum aestivum L.) and summer maize(Zea Mays L.)-was investigated.The experimental site belongs to the Yucheng Comprehensive Experimental Station(YCES) of Chinese Academy of Sciences(CAS) and has been used in studying the changes in soil aggregates and organic carbon storage under different tillage systems for 7 years now.NT,no-tillage with removed residue and organic fertilization(NTRR) and conventional tillage(CT) treatments were set up in the study.The impact of the three tillage systems on total soil organic carbon content and storage,water-stable aggregate stability,water-stable aggregate SOC content and storage,and relationship between total SOC content and water-stable aggregate SOC content were analyzed.Compared with CT,SOC content and storage,and water-stable aggregate mean weight diameter(MWD) and geometric mean diameter(GMD) along with macro-aggregate organic carbon content and storage in the 0~20 cm soil layer significantly increased in NT and NTRR treatments.This was possibly due to reduced soil disturbances and residue mulch and organic fertilizer applications.No tillage plots with residue mulch stored more SOC and macro-aggregate organic carbon than those with applied organic fertilizer.For the treatments,the order of the content of SOC and macro-aggregate organic carbon in the 20~60 cm soil depth was NT < NTRR < CT.In comparison with NT and NTRR,CT limited deep-soil organic carbon accumulation.Compared with straw mulch,the application of organic fertilizer enhanced deep-soil organic carbon accumulation under no tillage.On the average,SOC storage in NT and NTRR was lower than in CT in the 0~60 cm soil depth.There was a significant positive correlation between SOC and 0.25~2 mm aggregate organic carbon,indicating that the 0.25~2 mm soil macro-aggregates could be used as a proxy for changes in SOC.In conclusion therefore,no-tillage significantly improved the distribution and stability of surface soil water-stable aggregates.While no-tillage significantly increased the storage of surface total SOC in the 0.25~2 mm soil aggregates,reduced it in deep soil layers.Compared with organic manure,straw mulch promoted the accumulation of SOC in surface soils and reduces it in deep soils under no tillage practice.