绿肥粉垄耦合对稻田耕层土壤团粒结构特征的影响

目的]研究稻田生态系统耕层优化对双季稻田耕层土壤团粒结构特征的影响,为探明和评估绿肥粉垄耦合土壤物理结构特征及稻田土壤逆境调控提供理论依据.方法]2017—2018年在广西农业科学院试验田(南宁)开展为期4个稻季的定位试验,早稻采用粉垄耕作(F)和常规耕作(C)2种方式,以不施肥(N)为对照,设置常规施用化肥(N0)、同等肥力条件下单倍绿肥配施化肥(N1)和双倍绿肥配施化肥(N2),共设8个处理(CN、CN0、CN1、CN2、FN、FN0、FN1、FN2),晚稻实行常规施用化肥免耕.采用粒度分析仪测定0~15、15~30和30~45 cm耕层黏粒、粉粒、砂粒的土壤粒径含量;采用湿筛法测定0~15 cm层土壤水稳性团聚体含量,计算土壤水稳性团聚体凝聚力的关键指标,即平均重量直径(MWD)和几何平均直径(GMD);采用电子显微镜扫描团聚体超微观形态结构;采用土壤紧实度仪测定不同耕层土壤紧实度.结果]FN1处理提高了0~15和30~45 cm土壤黏粒含量,其中早稻分别增加0.75%和2.10%,晚稻分别增加0.67%和0.09%;FN2提高了除晚稻30~45 cm以外的其他耕层土壤粉粒含量.绿肥粉垄耦合能提高稻田土壤团聚体的凝聚效果.同一季稻田粉垄耕作土壤MWD和GWD均低于常规耕作,其中早稻和晚稻粉垄耕作土壤MWD较常规耕作分别降低0.19~0.96和0.47~0.72 mm,GMD较常规耕作分别降低0.36~1.52和0.79~1.15 mm.绿肥用量的增加有效提高了土壤MWD和GMD,其中FN1和FN2早稻处理下分别提高0.75和1.06 mm,晚稻分别提高0.21和0.31 mm.FN1处理提高土壤持水性和通气性,有效促进了土壤团聚体的形成.粉垄耕作下土壤微观结构呈孔隙多而偏小,空洞少而偏大的特征.晚稻FN1处理的土壤微团聚体和大团聚体含量最高,分别占8.60%和29.09%,免耕晚稻的土壤微团聚体和大团聚体含量较粉垄早稻有所提升,FN1处理增加了3.88%和1.34%,FN2处理增加了12.04%和9.01%.粉垄耕作下早、晚稻不同土层土壤紧实度均低于常规耕作,免耕晚稻的土壤紧实度高于免耕早稻.与常规耕作相比,FN1早稻土壤紧实度从土层自上而下分别降低8.90、22.73和55.15 kPa,晚稻分别降低1.20、28.84和53.93 kPa,FN2早稻分别降低5.80、25.37和66.00 kPa,晚稻分别降低6.80、36.97和50.33 kPa.结论]绿肥还田对粉垄耕作稻田土壤微形态结构特征产生重要影响,绿肥粉垄耦合有助于集约化水稻抗逆栽培、实现减肥增效.

Effects of green manure and smash ridging coupling on topsoil aggregate structure in paddy field

Objective]Studying the effects of topsoil optimization of paddy field ecosystem on the characteristics of soil aggregate structure in the topsoil of double cropping paddy field could provide basic data for explorating and evalua-ting soil physical structure characteristics and stress regulation under green manure and smash ridging coupling.Method]The field experiment was carried out in the experimental site of Guangxi Academy of Agricultural Sciences during the four seasons in 2017-2018. Early rice was cultivated by smash ridging(F)and conventional tillage(C)with no fertilization as the control(N),conventional fertilizer application(N0),single green manure with fertilizer(N1),double green manure with fertilizer(N2)under the same nutrient conditions were set,and a total of eight treatments(CN,CN0,CN1,CN2, FN,FN0,FN1,FN2),conventional fertilizer under no-tillage was adopted for late rice. Particle size analyzer was used to determine the content of clay,silt and sand particles in the 0-15,15-30 and 30-45 cm soil layers of paddy soil. The content of soil water-stable aggregates in 0-15 cm layer was measured by wet sieve method,and the key indicators of soil water-stable aggregates such as mean weight diameter(MWD)and geometric mean diameter(GMD)were calculated. The ultra-microscopic morphology of the aggregates was scanned by electron microscope. Moreover,the soil compaction characte-ristics of different topsoil layers were measured by soil compaction meter.Result]FN1 treatment increased the clay content of 0-15 and 30-45 cm soil in early rice seasons by 0.75%and 2.10%,while in late rice seasons increased by 0.67%and 0.09%. FN2 mainly increased the silt content of soil except in the late rice field layer of 30-45 cm. The condensation effect was improved by the green manure and smash ridging coupling on the paddy soil. In the same season,comparing with conventional tillage,smash ridging consistently reduced the soil MWD and GMD. The smash ridging of MWD in early rice seasons was 0.19-0.96 mm lower than conventional,and late rice seasons was 0.47-0.72 mm. The smash ridging GMD was 0.36-1.52 mm lower in early rice and 0.79-1.15 mm lower in late rice. The increase of green manure effectively improved the soil MWD and GWD,and FN1 and FN2 respectively increased by 0.75 and 1.06 mm in early rice,and the late rice increased by 0.21 and 0.31 mm respectively. FN1 improved the soil water retention and aeration ability,and effec-tively promoted the formation of soil aggregates. The soil microstructure characteristics under smash ridging showed the more pores with a smaller size,few voids with the larger size. In late rice seasons,the content of microaggregates and macroaggregates of FN1 was the highest,accounting for 8.60%and 29.09%respectively. The contents of soil microaggre-gates and macroaggregates of no-tillage late rice were higher than early rice with smash ridging,the content increased by 3.88%and 1.34%respectively in FN1,and 12.04%and 9.01%in FN2. The soil compaction of early and late rice smash ridging in different soil layers was lower than conventional tillage,and the soil compaction of no-tillage late rice was higher than of early rice. The soil compaction in the upper layer of FN1 decreased by 8.90,22.73,55.15 kPa in early rice and 1.20,28.84,53.93 kPa in late rice,respectively,while FN2 decreased by 5.80,25.37,66.00 kPa in early rice and 6.80,36.97 and 50.33 kPa in late rice,respectively.Conclusion]Green manure returning soil has an important effect on the soil micro-morphological characteristics of the smash ridging paddy field. The coupling of green manure and smash ridging is helpful to intensive rice art culture,reduce fertilizer and increase effect.