实施16年保护性耕作下黑土土壤结构功能变化特征

Changes of soil structure and function after 16-year conservation tillage in black soil

通过东北典型黑土区旱作平地连续16 a保护性耕作田间长期定位试验,研究保护性耕作实施后对土壤结构功能的影响,分析土壤结构功能的生育期动态特征及其与土壤有机碳的相关关系,探究作物产量变化的原因。以玉米-大豆轮作黑土农田为研究对象,设置4个耕作处理:秸秆覆盖免耕(No-tillage with straw returning,NT)和少耕(Reduced-tillage,RT)保护性耕作;平翻(Moldboard-tillage,MT)和旋耕(Rotary-tillage,Rot)传统耕作,探讨大豆幼苗期(Seeding-stage,SS)、开花期(Flowing-stage,FlS)、鼓粒期(Filling-stage,FiS)和成熟期(Maturing-stage,MS)耕层0~20 cm土壤容重、孔隙度、水分状况以及水稳性团聚体含量对耕作方式的响应。在大豆收获后取样测定不同耕作处理土壤有机碳的垂直分布和地表土壤水分入渗速率。结果表明:1)NT改善并稳定土壤结构。NT可以保持容重在生育期内的相对稳定;NT可以有效克服机械压实作用;表层土壤NT水稳性大团聚体(>0.25 mm)含量最多,平均重量直径(Mean Weight Diameter,MWD)高于其他耕作处理。2)NT提高土壤持水蓄水能力。NT增加表层0~5 cm土壤田间持水量;NT改善地表土壤水分入渗,整体初始入渗速率为其他处理的1.26~1.63倍,非种植带处稳定入渗速率为其他处理的2.24~6.63倍。3)NT显著增加土壤表层0~5 cm有机碳的积累,NT分别比MT、RT和Rot处理高32.59%、30.28%和25.79%。4)NT不会导致作物减产。长期连续保护性耕作尤其是秸秆覆盖免耕在改善土壤的结构功能,并显著增加表层土壤有机碳积累的同时,维持土地生产力,有效克服保护性耕作短期不良效应,提升黑土质量的作用明显。

Black soil rich in organic matter is one of the most fertile soils in Northeast China,one of the four largest black soil regions in the world.However,the structure and function of black soil have seriously deteriorated after long-term cultivation in recent years.Much effort has been made to ensure the sustainable development of black soil.However,most previous studies were focused on the soil structure and nutrients in the year of the experiment.In this study,a systematic investigation was performed on the soil structure and function during the whole growth period of crops,thereby elaborating the dynamic evolution after the long-term conservation tillage.A field test was also conducted in the Hailun Monitoring and Research Station of Soil and Water Conservation,Chinese Academy of Sciences(47°26′N,126°38′E),located at the Hailun City,Heilongjiang Province,the center of the typical Mollisols zone in Northeast China.Taking the corn-soybean rotation black soil as the research object,four tillage treatments were set(conservation tillage:NT(No-tillage with straw returning),RT(Reduced-tillage);traditional tillage:MT(Moldboard-tillage),Rot(Rotary-tillage))during the different growth periods of soybean(SS(Seedling stage),FlS(Flowering stage),FiS(Filling stage),and MS(Maturity stage)).Some parameters were measured,including the soil bulk density,porosity,water status,and water-stable aggregate content in response to tillage.Once the soybean matured,the soil samples were collected to quantitatively characterize the soil organic carbon in the vertical direction of different tillage treatments,and the soil moisture infiltration rate in the plow layer.The results showed that:1)The NT improved to stabilize the soil structure.The soil bulk density under the NT system was more stable than the other three treatments.The soil surface field capacity under the NT treatment was higher than that of conventional tillage during the whole growth period of soybean.The NT treatment increased the content of large aggregates on the soil surface and the Average Weight Diameter(MWD)was higher than the rest.The NT also improved the soil water infiltration,where the initial infiltration rate was 1.26 to 1.63 times that of the rest treatments.2)The NT significantly increased the accumulation of soil surface organic carbon.Specifically,the organic carbon content of soil surface under the NT treatment was 32.59%,30.28%,and 25.79%higher than MT,RT,and Rot treatments,respectively.3)The NT maintained the soil productivity.In short,the long-term no-tillage with the straw returning significantly determined the soil structure and organic carbon accumulation.The NT treatment performed better the structure and organic carbon accumulation in the lower layer soil,thereby promoting the sustainable development of black soil.This finding can provide a strong theoretical basis to explore the long-term effects of conservation tillage in the black soil area of Northeast China.