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

ObjectiveStudying 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.MethodThe 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.ResultFN1 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.ConclusionGreen 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.