稻田不同免耕轮作模式对土壤性质的影响

为研究稻田不同免耕轮作模式对土壤性质的影响,基于2004年在成都平原建立的耕作定位试验,以当地传统麦稻周年旋耕+无秸秆还田(CW-CR)模式为对照,设置麦稻周年免耕+秸秆还田(ZW-ZR)和油稻周年免耕+秸秆还田(ZO-ZR)2种免耕轮作处理,2014年后分层取样测试土壤物理、化学性质和主要酶活性。结果表明:和CW-CR相比,连续免耕配合秸秆还田促进土壤有机碳和碱解氮含量的提高,土壤表层(0～7.5 cm)增幅分别为41.3%～52.2%和33.6%～33.7%,差异达显著水平。免耕模式不同土层有效钾含量显著低于对照模式,降幅19.8%～25.7%。连续免耕促进直径2 mm的水稳性团聚体的大幅增加,但对不同土层容重、孔隙度和最大持水量等物理性质及土壤酶活性影响较小。周年免耕条件下,麦稻模式较油稻模式更利于表层土壤5 mm水稳性团聚体的形成,其他多数指标无显著差异。0～7.5 cm土壤质量指数(Soil quality index,SQI)排序为ZO-ZRZW-ZRCW-CR。连续免耕可以提高小麦和油菜产量,但水稻产量不及对照模式,ZW-ZR和ZO-ZR模式平均降幅8.7%和4.6%。本研究条件下,免耕可改善稻田土壤质量,ZO-ZR模式优于ZW-ZR模式,但土壤质量的改善与水稻生产力的提高不同步。

Soil properties affected by different rotation systems under long-term zero tillage in paddy field

The effects of different rotation systems under zero tillage on soil properties were compared in this study.A long-term experiment involving three cropping systems was established in Chengdu Plain in 2004,which were rotary tillage without residue retention under wheat-rice rotation,which was local conventional practice (CW-CR),year-round zero tillage combined with residue mulching under wheat-rice system (ZW-ZR) and zero tillage with residue retention under oilseed rape-rice system (ZO-ZR).After 10 completed rotations,soil samples were collected from four soil layers (0-7.5,7.5-15.0,15.0-30.0,30.0-45.0 cm) to determine its soil physical and chemical properties and enzyme activity.Compared with CW-CR,continuous zero tillage increased topsoil organic carbon and available nitrogen content by 41.3%-52.2% and 33.6%-33.7%,respectively.However,soil available potassium content was significantly reduced under zero tillage systems in all four soil layers.Zero tillage also had a potential to increase the formation of large water-stable aggregates (diameter>2 mm),while,it had little effect on soil bulk density,porosity,maximum water holding capacity and enzyme activity.Under continuous zero tillage system,wheat-rice rotation was more favorable to the formation of water-stable aggregates with diameter more than 5 mm in the topsoil than oilseed rape-rice rotation,and there was no significant difference in other parameters for two systems.The highest soil quality index (SQI) in 0-7.5 cm soil depth was recorded in ZO-ZR,and the lowest was in CW-CR.Moreover,zero tillage was favorable for wheat and oilseed rape growth,but decreased rice yield by 8.7% and 4.6% averagely due to poor irrigated water retention.In the present study,zero tillage is beneficial to improve soil quality,especially ZO-ZR practice,but limits rice production incensement.