不同还田方式对砂质潮土理化性质及微生物的影响

为探索不同物料还田方式对中低产田砂质潮土的改良效果,在黄淮海平原麦玉轮作区典型砂质潮土上进行了连续6季的田间小区试验,设置全量秸秆翻耕还田(TS),秸秆等碳量的生物炭(TB)及半量秸秆半量生物炭配合翻耕还田(TSB),全量秸秆免耕覆盖还田(NTS)和半量秸秆半量生物炭配合免耕覆盖还田(NTSB),共5种还田方式。结果表明,与常规秸秆翻耕还田(TS)相比,生物炭翻耕还田(TB)显著降低土壤容重,增加玉米各个生育期土壤水分和p H值,有机质含量提升了16.4%,但TB处理的土壤大团聚体降低了21.2%和微生物数量降低了16.1%;翻耕秸秆配合生物炭还田(TSB)除了显著降低了大团聚体数量,对其余理化及微生物指标的影响均不显著;免耕模式下的秸秆还田(NTS)和秸秆生物炭配施(NTSB)分别在玉米生长的喇叭口期和收获期显著增加了土壤水分含量、耕层土壤的微生物数量和有效降低砂质潮土分形维数,对容重和有机质含量有一定的改善,其中NTSB有机质含量提升了14.9%和微生物数量增加了53.7%,对砂质潮土改良效果更好。总体来说,短期内用等碳量的生物炭替代秸秆翻耕还田更多的表现为物理的掺混效应,虽能有效提升土壤有机质含量,但不能有效改善砂质潮土的物理结构及生物性质,一半秸秆用生物炭替代还田对该类土壤的理化及微生物指标的改良效果也不显著,而免耕条件下秸秆配合生物碳还田效果最佳,可为砂质潮土的改良提供新的途径和理论依据。

Effects of the return of organic materials on soil physical and chemical properties and bacterial number in sandy soil

Sandy soils have limitations for growing crops. In general, those soils have poor structural traits, low fertility, and little organic matter. Agricultural practices influence the physical and chemical characteristics of soil and induce changes in soil microbial structure and function. It was important to determine a conventional agricultural practice to improve the quality of soil and solve the problem of the reduced productivity. The effects of different tillage practices on physical, chemical, and microbial properties of the soil have been studied. Organic matter is crucial for soil productivity and its quantity depends heavily on soil management systems. Returning crop straw to fields is one of the common practices to improve soil organic matter and achieve sustainable development of agriculture. Biochar, a solid elemental carbonaceous material, formed from the thermochemical conversion of biomass in an oxygen-limited environment, is a much more durable form of C than parent plant biomass or most forms of C in soil organic matter. Hence, the application of biochar to soil has been proposed for increasing the stable C pool and improving physical and chemical properties of soil. No-tillage and direct seeding are believed to be more sustainable than conventional practices, mainly because they improve nutrient status and water conservation. Although there have been many studies that referred to no-tillage and straw return or biochar application separately, the combined effects of various tillage and organic materials returned to sandy soil in the Huanghuaihai Plain requires further research. To address the adverse physical and chemical characteristics of the soil, a field experiment was conducted in a sandy fluvo-aquic soil in a village near Xinzheng City, Henan Province, to assess the effect of five methods of organic material return. The five methods were equivalent in the amount of carbon application, and included conventional tillage combined with straw return (TS), conventional tillage combined with biochar application (TB), conventional tillage combined with half straw and half biochar application (TSB), no-tillage combined with straw cover (NTSB), and no-tillage combined with half straw and half biochar cover (NTSB). The results indicated that compared with TS, the most popular local agricultural practice, TB significantly decreased soil bulk density, and increased soil water content and pH value. The soil quality index of soil organic matter increased by 16.4%. However, TB decreased the soil macroaggregate number and bacterial gene copy number by 21.2% and 16.1%, respectively. Compared with the available carbon component of straw, the chemical stability of biochar decreased microbial growth to some extent. TSB without any significant effect on soil chemicals or microbial shifts could significantly decrease soil macroaggregate number. NTS and NTSB, the two no-tillage practices could significantly increase the soil water content in the maize growing stages, bell mouth and ripening, separately, and NTSB dramatically increased bacterial number and soil organic matter by 53.7% and 14.9%, respectively, and decreased the soil fractal dimension, which increased the amount of macroaggregates and its stability. Compared with the common practice of conventional tillage with straw return, no-tillage combined with straw and biochar return is an effective way to change physical, chemical, and microbial properties of sandy soil, and the results will provide some theoretical basis for improving other low-yield soils.