| With increasing crop yields, how to reasonably and effectively dispose the crop straw residues is becoming a pressing issue agricultural production for China. Returning to fields as an effective way has been vigorously promoted, however, there are some drawbacks for the conventional methods (straw mulching and rotary tillage return) such as difficult to return full amounts in high or super-high yielded conditions, lots of straw residues concentrating in topsoil easily causes difficulties for machinery tillage, returning too shallow leading to fast decomposition of straws limited the carbon sequestration, and make against deepening the plough horizon.In the past 20 years, there was few innovative research of soil tillage was conducted in rice-wheat rotation system. Searching an effective technical way of straw return and soil tillage with total amount, convenience, cleaning and security has become an urgent and important subject in farming system research.Few studies reported the effects of ditch-buried straw return on crop growth and soil conditions. This study designs four treatments with different buried depths, buried amounts, ditch widths and ditch spaces. The control treatment was defined as conventional tillage (without straw returning and ditches). Through a four-year field experiment, focused on the effects of soil physical properties in wheat season, the soil nutrient and organic carbon content in rice season with different buried depths (10cm,20cm,30cm and 40cm) and buried amounts (half, total, and twice amounts). We obtained the following conclusions:1) Make the soil physical environment better be propitious to the growth of wheat.Ditch-buried straw return of buried 20cm and 40cm could decrease the soil bulk density, increased soil non capillary porosity and total porosity, the effects of upper soil adjacent straw layer was very obvious, and the decreasing and increasing effects could last for a long time. Straw ditch had the function as "dewatering culvert", which was propitious to decrease soil moisture quickly after heavy rainfall in wheat season. The closer straw and drainage ditch after rainfall, the soil moisture decreased more rapidly, the decreased effects were better than CK at 10cm near straw ditches of different buried depths. The water reducing order of ditch-buried depths was 30cm> 20cm> 40cm> 50cm. the soil water potential totality showed declining trend with the extension of time after rainfall. Different determined position of ditch-buried 40cm was lower than other treatments and CK, which illustrated that the more deeply straw buried, the more conducive to the soil drainage of wheat. For soil water potential decline range, ditch-buried 20cm showed obvious advantage of drainage than the other treatments.2) Reduced the total nitrogen content of top soil in straw buried ditch, and increased the soil available P and available K content of the soil above straw.The total nitrogen content of different soil layers in straw buried ditch changed larger after the straw was return by ditch-buried.0-10cm soil layer of each returning time with ditch-buried 10cm decreased to different extent than CK. If the ditch-buried deeper, the surface soil of other treatment also showed the phenomenon of significantly lower than CK. In addition to ditch-buried 10cm, the soil total nitrogen of upon straw layer of other buried depths after different incorporation time was increased in different degrees. The more incorporation deeper, the increased effects more obvious. The available P and available K content of different ditch-buried depths and amounts in each soil layer increased in varying degrees after rice and wheat straw ditch-buried return, and the soil available K of buried straw ditch increase a large amount in early days.3) Both soil total organic carbon (TOC) and soil active organic carbon (AOC) content increased in different soil layers under different ditch-buried straw return with full amounts, meanwhile showing better increase effects of soil carbon pool management index(CPMI) than half and twice amounts.Irrespective of the buried depths and amounts, the treatments of soil layers, returning time and their interactions significantly affected TOC, AOC and CPMI. With increased of straw buried depth, the TOC content of each soil layer of different depths and returning time with total amounts increased to different extent. Especially in the upper soil near the straw layer were increased significantly. Different buried depths could increase the AOC content of each soil layer. Especially for two soil layers closed to straw, the relative growth rate with CK was more obvious. In the treatment of different buried amounts, the increased rate of half amounts in the soil upon straw was obvious lower than total amounts, but twice amounts was significantly lower than CK. Different buried depths could increase CPMI in different soil layers. With increasing the buried depths, increased more significantly in the soil layer near straw. The total amounts showed a better increasing effect than half and twice amounts, especially for the two soil layers nearby straw layer. The soil CPMI near straw layer of half and twice amounts showed a phenomenon of lower than CK, which explain that total amounts was conducive to the development of soil quality, and had fertilizer effect on soil.4) After four consecutive years of ditch-buried return, decreased the soil total nitrogen content of 0-10cm soil layer, increased soil available phosphorus content, reduce soil available potassium content of 0-10cm soil with ditch-buried 30cm and 40cm.After four consecutive years of ditch-buried return, the total nitrogen content in 0-10cm soil layer with four ditch-buried depths was decreased in different degrees. While ditch-buried 20cm,30cm and 40cm significantly increased the total nitrogen content of the soil layer upon straw, and ditch-buried 30cm and 40cm also significantly increased the total nitrogen content of the soil layer below straw. Three buried amounts all significantly decreased soil total nitrogen content of other two layers except the soil layer upon straw (10-20cm). Different ditch-buried depths and amounts could significantly increase the soil available P content in each soil layer. In addition to ditch-buried 30cm and 40cm had different degrees of reduction of soil available K content in 0-10cm soil layer, other depths significantly increased in each soil layer. Ditch-buried deeper, with the higher increased rate than CK.5) After four consecutive years of ditch-buried return, the soil organic carbon increased significantly.Compared with CK, each soil layer of different buried depths and amounts were significantly higher. The increment rate of TOC in deep soil was increased with the buried depth, and also increased significantly to the soil below straw layer. The increasing effect of total amounts was significantly higher than half and twice amounts. Different buried depths significantly increased AOC content compared with CK in each soil layer, especially for the two soil layers near straw. Different with TOC, the AOC content of ditch-buried 10cm and 20cm in the soil upon straw (0-10cm and 10-20cm) was the highest, while 20-30cm and 30-40cm soil layer was ditch-buried 40cm had the highest AOC content. In different buried amounts, total amounts had the highest AOC content in three soil layers. Twice amounts significantly reduced the AOC content of 10-20cm layer. |
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