绿肥粉垄耦合对稻田耕层土壤团粒结构特征的影响（英文）

郑佳舜　胡钧铭　韦燕燕　李婷婷　苏世鸣　韦翔华　何铁光　夏旭

摘要：【目的】研究稻田生態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。

关键词： 绿肥还田;粉垄耕作;稻田土壤;土壤团聚体;微观结构

基金项目：国家自然科学基金项目（41661074）;广西第二十一批“十百千人才工程”专项（2018221）;广西创新驱动重大专项（桂科AA17204078-2）;广西农业科学院科技发展专项（桂农科2017JZ09）

Effects of green manure and smash ridging coupling on

topsoil aggregate structure in paddy field

ZHENG Jia-shun1， 2， HU Jun-ming1* ， WEI Yan-yan2， LI Ting-ting1， SU Shi-ming3，

WEI Xiang-hua2， HE Tie-guang1， XIA Xu3

（1Agricultural Resource and Environment Research Institute， Guangxi Academy of Agricultural Sciences， Nanning 530007， China; 2College of Agriculture， Guangxi University， Nanning  530004， China;3Institute of Environment

and Sustainable Development in Agriculture， Chinese Academy of Agricultural Sciences， Beijing  100081， China ）

Abstract：【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 ultramicroscopic 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 effectively 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 microaggregates 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.

Key words： green manure returning soil; smash ridging; paddy field soil; soil aggregates; microstructure

CLC number： S152.4                              Document code： A      Article：2095-1191（2020）11-2653-12

0 Introduction

【Research significance】Modern intensive agriculture relies too much on fertilizer input，which was not conducive to the balance of nutrient supply between soil and crops and led to more and more serious environmental problems such as soil acidification and soil hardening（Yuan et al.，2011）. In order to reduce the amount of national farmland fertilizer consumption and increase the efficiency，the transformation of agricultural practices had emerged as an important method of green agricultural development in the new period in the modern China. Rational utilization of green organic resources to replace chemical fertilizers was of great practical significance to explore the stable input of agricultural organic resources to regulate the transformation of soil into healthy topsoil and promote the zero increase in chemical fertili-zers.【Research progress】Soil aggregates affect the quality of profile soil and restrict soil structure and stability. Research of agricultural organic resources in soil showed that 90% of the organic matter was found in the soil aggregates（Dou et al.，2011）. The revival of organic matter to the field not only increased the content of soil aggregates，but also improved their stability（Zhang et al.，2017a; Liu et al.，2014）. As the essence of traditional agriculture，continuous planting of green manure could improve soil mechanical ability and water-stable aggregates content（Zhang et al.，2018）. Soil carbon input was affe-cted by green manure（Astragalus sinicus L.） retur-ning to the field，the soil carbon sequestration was better when green manure was applied to the soil（Zheng et al.，2019），and it could significantly increase the content of soil particles（Wu et al.，2005）. Soil compaction affected the composition and stability of soil aggregates，it could promote the transformation of microaggregates of intermediate particle size either to larger ones or disperse to aggregates of smaller ones（Lu et al.，2015）. Soil particle size affe-cted soil compaction which resulted in a decrease in soil porosity，and the air void of heavily compacted soil dropped below 3%，leading to friction between soil aggregates，poor stability，and enhanced activity of anaerobic microbe in the soil，and weakened aerobic microbial activity（Nawaz et al.，2013），which the higher the soil compaction，the lower the soil microbial activity（Ishak et al.，2016）. The large area use of some small mechanical tillage caused shallow farmland layer and poor physical structure，reduced the ability of soil to retain water and fertilizer，and affected crop growth and stable high yield（Tang et al.，2019）. The properties of soil suitable for cultivation and fertility control affected the construction of soil healthy arable layer（Hu et al.，2018）. Studies showed that tillage activities created favorable conditions for the decomposition and transformation of soil organic carbon，and tillage methods affected the formation of micro-aggregates in large aggregates and the fixation of soil organic carbon，and there were differences between different tillage intensities（Liu and Yu，2011）. 【Research breakthrough point】As a new type of deep rotary plowing，smash ridging was widely used in agricultural production，which used drill bits with spiral blades perpendicular to a depth of 40-50 cm in the soil，and with the high horsepower and intensity tillage method，in-situ rotary grinding crushed soil blocks，removed the soil barrier，to achieve the purpose of loosening，activating the deep soil，and increasing the surface thickness（Wei et al.，2012; Zhang et al.，2017b）. Smash ridging broke the bottom layer of soil plow，whether transversal cutting affected soil structure and soil environment was a problem that the industry paid special attention. 【Solving problems】The green manure retur-ning to paddy fields had an important effect on soil microstructure and morphology characteristics，and the green manure and smash ridging coupling was helpful to reduce fertilizer application and increase its effect in intensive paddy field.

1 Materials and methods

1. 1 Survey of the experiment site

The rice plants were grown in the paddy field of Nanning experiment site of Guangxi Academy of Agricultural Sciences（22°50′N，108°24′E） in 2017-2018. The experimental area has a subtropical monsoon climate and abundant hydrothermal resources. The soil pH was 6.60，contained total nitrogen 1.80 g/kg，total phosphorus 0.92 g/kg，total potassium 7.43 g/kg，hydrolytic nitrogen 131.00 mg/kg，available phosphorus 37.90 mg/kg，available potassium 97.80 mg/kg，organic matter 24.50 g/kg. Early rice green manure for fresh A. sinicus（dry basis nutrient was 2.7% N，0.65% P2O5，2.5% K2O），which was consistent with the minimum nutrient ratio of conventional fertilizer application（N 240 kg/ha，P2O5 120 kg/ha，K2O 240 kg/ha），balanced with chemical fertilizer. Fig.1 showed the field operation method of returning green manure on paddy fields under smash ridging. Chemical fertilizer application included urea（46% N），calcium superphosphate（15% P2O5），potassium chloride（62.7% K2O） and compound fertilizer（15% N，15% P2O5 and 15% K2O）.

1. 2 Field management

Conventional tillage is limited by power and limited to 10-15 cm of deep tillage，which rarely pushes the soil below the mellow soil layer. Samples of this experiment were collected in 2018. Two til-lage methods were set up in the experiment（conventional tillage and smash ridging），and four fertilization methods were set for early rice，and no fertilization was used as the blank control，under the same nutrient condition，conventional fertilizer application was used as the reference standard. There were eight treatments，each of which was repeated 3 times（Table 1）. The scale of the plot was 7.4 m×6.2 m，and the rice varieties tested were indica three line super rice （Teyou 582）. The rice was transplanted with 12 cm×24 cm plant spacing and 2 seedlings inserted in each hole point. Field management was conducted according to conventional super rice production.

1. 3 Sample collection and analysis

Soil samples of 0-15，15-30 and 30-45 cm in 2018 were analyzed in the early and late rice harvest period，and repeated for three times in each plot. The laser particle size analyzer Mastersizer 3000 produced by Malvern company in the UK was used as already described（Li et al.，2019）. At the same time，the soil compaction of 0-45 cm soil layer was measured by Digital Soil Compaction Meter SC900 du-ring early and late rice harvest twice，and each plot repeated ten times.

The content of clay particles which under 15-30 cm in smash ridging was significantly lower than that in conventional tillage after applying green manure，but FN2 was higher than CN2. The increase of green manure under the smash ridging reduced the clay particle content of the double cropping paddy soil，characterized by FN0>FN1>FN2，there were significant difference in early rice. The content of soil silt in conventional tillage was lower than that in smash ridging，but the N1 treatment was the opposite. Under the smash ridging，FN2>FN1，and the FN2 and FN1 were significantly higher than FN0 in early rice but significantly lower than FN0 in late rice. The content of soil sand characterized by FNCN1 in double cropping paddy soil，but the content of soil sand in single green manure characteri-zed by FN2>CN2 in early rice but FN2

In 30-45 cm of topsoil，soil clay content particles of FN2 in early rice was significantly lower than CN2，and the other treatments showed that conventional tillage was significantly lower than smash rid-ging，and in late paddy soil was characterized by FN1> CN1，and another conventional tillage was higher than smash ridging under other the same fertilization. FN2 was significantly lower than other treatments under the smash ridging in early rice but hig-her in late rice. The silt content in the same fertilization method was basically the same as that in the 15-30 cm soil layer，but FN1FN1 in double cropping rice 30-45 cm sand content particles，and the smash rid-ging and green manure coupling was higher than FN0 in early rice，but lower in late rice.

2. 2 Effects of green manure and smash ridging coupling on water stability aggregates

The composition of soil water-stable aggregates in paddy field by smash ridging was shown in Table 3，the aggregate content ofⅠlevel in early rice ordered in FN2>FN1>FN0，and FN0 was significantly lower than other treatments. Under the same fertilization，smash ridging were lower than conventional tillage，there was significant difference in late rice，the content of soil water stability aggregate of FN1 was the lowest in late rice. Under the same fertilization，the content of early and late rice water stability aggregate by smash ridging in Ⅱ-Ⅶ levels were higher than conventional tillage，which in Ⅵ level of late rice showed significant difference，early rice on other graded FN0 except Ⅰ level were higher than other processings，and Ⅱ，Ⅲ，Ⅴ levels showed significant difference. Under the conventional tillage，the Ⅲ and Ⅳ level both showed the CN0>CN2>CN1，and under the smash ridging showed Ⅲ level of FN0>FN1> FN2，Ⅳ level of FN1>FN0>FN2. The Ⅳ，Ⅴ level also performed as smash ridging was FN1>FN2，there was significant difference in late rice at Ⅳ level. The FN1 in Ⅵ level，FN2 and FN1 in Ⅶ level in late rice were significantly higher than conventional tillage. It was obvious that the soil microaggregates（<0.25 mm） and medium aggregates（2.00-0.25 mm） under early and late rice smash ridging were always larger than conventional tillage，and the content of microaggregates and medium aggregates under single green manure application to the field was higher than double green manure.

The higher the MWD and GMD，the more stable the soil aggregates and the stronger the soil an-tierosion ability，and the higher condensation effect（Han et al.，2018）. Under the same fertilization，the soil MWD and GMD by smash ridging were lower than conventional tillage. The MWD of CN1 was the highest in conventional tillage and FN2 was the hig-hest in smash ridging，GMD also presented the same trend. Comparing with late rice，only FN0 showed an increase in MWD and GMD，while other treatments of late rice were lower than those of early rice. The MWD with green manure under the conventional til-lage decreased by 0.04-0.10 mm，and the MWD with smash ridging decreased by 0.32-0.41 mm，so smash ridging played a major role in the change of soil aggregate structure. It was not difficult to find that the same season soil in the paddy field could promote the condensation effect of the aggregates on the soil under the same smash ridging not as good as conventional tillage，but the soil aggregates of early rice under smash ridging could be effectively improved by increasing green manure.

2. 3 Changes of soil microstructure under diffe-rent magnifications

2. 3. 1 Soil microstructure magnified 2000 times

The soil aggregate surface results were shown in Fig.2 which were magnified 2000 times，it could be directly seen basic skeleton from the SEM images. The early rice blank control CN soil was mainly filled with composite packing，had relatively smooth big bone shape in bulk，the few scales particles to attach with a small dot or column attached around. Compared with the FN cultivated by smash ridging under the presence of massive structure with occasionally visible hole in the block structure of microvoid，and the layered structure of soil was relatively clear，with irregular light flocculent attached around. The above characteristics were basically maintained in the two tillage methods under different applications. Compared with FN，the FN0 channel was mainly linear，and the facade appear to be more compact. It could be clearly seen that the number of large pores in the four treatments with green manure（N1 and N2） was more than that in N and N0，the number of pore also increased，and the depth of depression was larger. The flocculent attached by FN1 and FN2 had a clear wheel frame，and the flocculent shape of FN1 changed to the sharp angle shape. CN under no-tilla-ge in late rice was more fine bone particles compact than early rice，and the original smooth soil clods grew more compact spherical particles. The small flower shape of CN0 soil surface material disappeared，and only the smaller spherical particles remained than CN in late rice. The growth of soil attachments in FN was faster than CN and were closely packed，but still clear to see smash ridging form the small aperture. Under the chemical fertilizers，irregular small flower shape soil adhesion was observed，while CN1，FN1，FN2 still kept the flocculent stretch. CN2 soil was planar，attachments were reduced，and after green manure application，there were more voids in the smash ridging than conventional tillage.

2. 3. 2 Soil microstructure magnified 5000 times

The surface structural characteristics of soil aggregates were exposed gradually and observed more clearly from SEM images under a high magnification of 5000（Fig.3）. The application of single ferti-lizer and green manure in early rice under conventional cultivation had a great difference on the growth and morphology of soil surface adhesion. The microscopic morphology of the soil with CN as the background showed that the soil was in strip form and little ball attachment. After applying fertilizer（CN0），the attachment presented a relatively dense small flower shape. With the increase of green manure，in addition to the increasing number of flocculent，CN1 channel number was more，CN2 was ob-viously voided，and the soil showed a short form of attachment. Compared with conventional tillage，the soil presented a vertical and fluffy shape under the early rice smash ridging. The attachment on the top layer of FN1 soil under the magnification of 5000 times could see the basic form of rotation in the SME image，and the flocculated，angle was deve-loped under the whole soil under the background of plane shape. The soil micromorphology of CN0 in late rice grew outwards，forming an accumulation structure，there were more flower particles and some of them extended outwards compared with early rice. However，FN0 presented a honeycomb shape and clearly showed the track left by mechanical cultivation. But the soil of FN，FN1 improved soil original rotating structure to sheet transformation under the smash ridging，FN remained porous，loose gap pre-sent stalactite shape，elliptical particles attached arrangement，the soil of FN1 was dense and more porous with smaller size，less voids with the larger size. The difference between CN2 and FN2 was more ob-vious，CN2 soil showed plate and no voids，and FN2 not only increased soil fleeciness degree but also had a good bedding structure on the surface of the soil.

2. 3. 3 Soil microstructure magnified 10000 times

It was more obvious than other magnifications that the micromorphology of soil aggregates presented different colors with different treatments under 10000 times magnification（Fig.4）. The color could not only describe the hierarchical structure of the soil，but also characterized the morphological characteristics of soil under different treatments. The application of green manure in early rice increased the input of soil organic resources. CN1 and CN2 showed a small area of separate gray and white color under conventional tillage and green manure，but under smash ridging，there were generally evenly distribu-ted two to three different colors： greyish white，gray and dark gray. FN1 was distributed in scales，and FN2 was extended in flocculent. The SEM of the soil under no-tillage of late rice listed the color characteristics of early rice. The paddy soil treated by conventional tillage gradually developed into cracks，blocks and flakes，while the flocculent attachment of FN1 was still metabolized at a slow speed. Because the smash ridging of early rice increased the depth of cultiva ted soil，changed soil characteristics，and the soil was porous，the green manure application in an early rice to the field had a certain influence on the stimulation of the evolution of surface in late rice.

2. 4 Effects of green manure and smash ridging coupling on soil compaction

The law of soil compaction was different in di-fferent soil layers（Fig.5）. In general，the soil compaction of late rice was higher than early rice，the compaction of soil under smash ridging was always lower than conventional tillage，generally the soil compaction increased with the increase in soil layer under conventional tillage，and the soil compaction increased slowly under smash ridging at a depth of 30-45 cm. Soil compaction of early and late rice under 0-15 cm was different under smash ridging，and late rice under different treatments was higher than early rice at 7.23-11.60 kPa. Under conventional tillage and smash ridging of rice，soil compaction was decreased with the increase of green manure. FN1 and FN2 were lower than other treatments，the difference was in early rice. FN1 decreased by 8.90 and 1.20 kPa respectively in comparison with CN1 in early and late rice，and FN2 decreased by 5.80 and 8.80 kPa respectively in comparison with CN2 in early and late rice.

The soil compaction of 15-30 cm paddy field under smash ridging was FN2

3 Discussion

The sand particle contents in the topsoil was decreased by smash ridging，the optimized model of coupling smash ridging and green manure effectively increased the content of fine particles in 0-15 cm soil. Previous studies found that soil microbes with high sand content had a short turnover period，and organic matter was easy to be degraded by microbes，while clay and silt particles were closely related to the microbial turnover period，which was more conducive to the maintenance of soil nutrients（Chen et al.，2002）. According to the existing studies on the distribution of soil organic carbon pool in soil，the carbon input of organic resources increased the carbon storage in soil clay and sand，and an increased rate of clay was much higher than sand（Zhang et al.，2012）. At the same time，the storage of organic carbon in silt particles decreased gradually，and the carbon sequestration efficiency was lower than clay and sand（Cai et al.，2015）. In this study，single green manure increased soil clay particles，and double green manure increased silt particles respectively. Clay particles were regarded as the main solid components of organic carbon in red soil（Mendes et al.，1999），organic carbon content of clayey soil was higher with larger surface area，and the greater charge density with stronger adsorption of soil organic carbon，and macromolecular organic matter form relatively stable organic-inorganic compound，and further form a more stable aggregate structure to achieve a good protection of soil organic carbon，soil enzyme activity of maximum also appears in the aggregate particle size small（Mendes et al.，1999; Ren et al.，2007）. Therefore，returning single green manure to the field had a positive influence on the accumulation of soil carbon pool and the operation of carbon.

The single green manure and smash ridging coupling were conducive to increase the content of micro，small and medium water-stable aggregates in the paddy soil. According to the development model of soil aggregates classification，the formation of soil aggregates from microaggregates to macroaggregates was continuous and hierarchical，and microaggregates were more stable than macroaggregates，which was a prerequisite for the formation of macroaggregates（Tisdall and Odaes，1982; Elliott，1986）. The formation of macroaggregates in soil mainly depen-ded on the formation of organic residues and myce-lium cementation，and soil particles transformed into microaggregates and macroaggregates under the action of cementing substances，fungal hyohae and root system（Yang and Zhang，2011; Bai et al.，2019）. In this study，smash ridging increased the soil micro，small and medium water-stable aggregate contents in the paddy field. Previous studies showed that the change in agricultural soil over a time could lead to a gradual recovery of background soil under different tillages practices，the large aggregates of organic resources for soil water stability decreased continuously，while the content of micro aggregates increased gra-dually and the soil water-stable aggregates changed from large particle size to small grain size （Li et al.，2017）. The cultivation disturbance accelerated the renewal of soil macroaggregates，and the number of microaggregates in macroaggregates was greatly reduced（Liu and Yu，2011）. Combined with soil water-stable aggregates and soil micromorphology analysis results，under conventional tillage soil was mainly filled with composite packing，which presented relatively smooth and big bone shape in bulk，the few scales particles attached around. Smash ridging soil showed a massive structure with occasionally seen hole in the block structure of micro-void，the layered structure of soil was relatively clear，the periphery was attached to form a protective layer with irregular light flocculent，and the tiny particles wrapped in the aggregates were more physically protected，all of them explained the better results. In present study，the authors have applied a no-tillage strategy with green manure application in late rice to reduce the damage degree to soil aggregates，and to effectively regulate the stress on topsoil which played a protective role in optimizing the quality of soil and improve the stability of soil aggregates.

The soil after early rice smash ridging was vertical and fluffy，and under no-tillage in late rice，the fertilizer was applied to keep the soil loose and porous. Green manure application could effectively improve the condition of soil aggregates in early rice under smash ridging and improve the recovery effect of soil condensation，and also promote the development of soil micromorphology. The studies related to growth pattern of early and late rice was slightly different from the above results，this may be related to climate factors. There were more macropores in the small aggregates，and the total pores and pore surface area of the soil formed by them were large，which was conducive to the root system of crops and the absorption of water and nutrients by plants（Bailey et al.，2013）. Green manure application could rapidly increase the organic carbon content in surface soil and also enhanced the water stability of aggregates to provide a good organic cementing agent for soil，which could cement small aggregates and promote the formation of large aggregates（Miao et al.，2009）. The application of single green manure provided an effective medium for soil aggregates in the unsatura-ted range，it was beneficial to loose soil texture，improve the water permeability，promote the healthy and stable development of plant root activity and microbial activity，increasing the input of exogenous organic crops would enhance soil aeration and accelera-te the decomposition rate of organic carbon，which could be used in better growth of crops（Schlesinger and Andrews，2000;Xiao et al.，2005）. In this study，there was difference in soil micromorphology between chemical fertilizer and without fertilizer under conventional tillage. The soil micromorphology under conventional tillage showed that peripheral fine debris grew to a small flower shape，and the basic skeleton expanded slightly，with the change of time，the soil attachment of late rice with no-tillage disappeared and formed spherical particles. It was different from Sun et al.s（2016） observation results of soil micromorphology with fertilizer application，it may be related to different soil properties，tillage depth，fertilizer application and field management mode. Smash ridging broke the bottom layer of the plow effectively，the soil was compact and keep the more pores with smaller size，less voids with larger size，and with good connectivity. The input of green manure was mainly through the exogenous carbon to increase soil carbon sequestration capacity，which was more easily embedded into deep soil microaggregates after the treatment of smash ridging. It could improve deep soil physical and chemical properties，improve soil water capacity and aeration，and effectively promote the formation of soil aggregates.

The compaction of different soil layers in early and late rice decreased by smash ridging，and the compaction of no-tillage soil in late rice was higher than that in early rice. Smash ridging extended the depth of the topsoil，increased the activities of soil organisms，and affected the coordination and effectiveness of soil nutrients，moisture，aeration（Zhu et al.，2004）. In this study，smash ridging had a direct impact on the compaction of the soil layer from 15-30 cm depth. The soil compaction increased slowly at the depth of 30-45 cm，and the restoration of compaction of the soil layer was slow after late rice cultivation. Compared with application of chemical ferti-lizer，the compaction of soil of 0-15 cm decreased by the application of green manure in smash ridging，and the compaction of soil after the application of double green manure was lower than that of single green manure application，which provided a good foundation for the improvement of soil quality in the topsoil.

4 Conclusions

Smash ridging formed more porous characteristics with small size and fewer voids with the larger size. The optimization model of smash ridging and single green manure（35586.65 kg/ha） returning to field not only inhibited the degradation of the smash ridging soil structure effectively，but also reasonably controled smash ridging soil disturbance in changed soil aggregate condensation effect and increased the fine particles in the soil and reduce soil compactness. It is helpful to strengthen the soil periodic opera-tion，and improve the sustainable development of soil resources in paddy field and intensive the rice art culture，reduce fertilizer to increase effect in pa-ddy field，to achieve soil ecosystem restoration and degradation of soil quality perspective. Other relevant studies on the spatial structure of soil under the green manure and smash ridging coupling need to be further discussed.

5 Acknowledgements

We thank Yang Ren-xiang（Agricultural College，Guangxi University，Nanning，China），Yuan Jia-kai（Civil and Environmental Department，Enginee-ring College，Northeastern University，Massachusetts，Boston， USA） for them help in experiments and English manuscript writing，respectively，and we thank Science Editing for editing this manuscript.

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（責任编辑 陈德元）

Received date：2020-03-04

Foundation item：National Natural Science Foundation of China（41661074）; Talent Project of the Hundred， Thousand and Ten Thousand of Guangxi（2018221）; Guangxi Innovation Driven Major Project（Guike AA17204078-2）; Science and Technology Development Plan Project of Agricultural Resource and Environment Research Institute（Guinongke2017JZ09）

Biography：* for corresponding author， HU Jun-ming（1974-）， doctor，researcher， interested in the organic resource utilization，habitat regulation and adverse ecology，E-mail：jmhu06@126.com. ZHENG Jia-shun（1995-），interested in soil environment and ecology，E-mail：ashunz08@163.com