Effect Of Corn Straw Returning On Soil And Water Conservation In Slopping Farmland Of Black Soil Region

The Northeast black soil region is the significant commercial food base of China,but the area of slopping farmland has occupied about 60%of dryland area.Unfortunately water-induced soil erosion has become a serious problem and kept developing in the future for Northeast China's Mollisols as the natural factor and large-scale intensive cultivation which has become common across these landscapes.This serious problem has become a threat for the food security in China.It is well known straw returning can reduce the effect of splash erosion for raindrops on soil surface and increase the soil infiltration rate,thus straw returning has a positive effect on soil conservation.At present,it is the common method for the conservation work in Northeast that most straw are buried by ploughed tillage in subsoil.Most studies focuse on the soil quality recovery of straw returing,while few research reports the soil conservation effect of straw returing in Northeast China.Hailun Monitoring and research station of soil and water conservation,a typical black soil region with sloping farmland in Northeast China,was chosen as the research area in 2015²016.We choosed no-tillage with straw mulching?NTS?and straw incorporation through plow tillage?PTS?as the straw returning modes in our study.And the runoff plot in sloping farmland was used to study the effect of two straw returning modes on the soil and water conservation,soil physical properties,soil nutrients and the characteristics of straw decomposition and nutrient release.The results showed:The treatments of NTS and PTS could effectively reduce soil loss and surface runoff in Black soil region in Noetheast China.Compared with the treatment of conventional tillage?CT?,the soil water storages in 0¹50 cm soil layer and soil initial infiltration rate in 0¹0 cm soil layer were increased by 3%and 19.3%in the NTS;the number of annual surface runoff and soil loss in the NTS were 4 times and 3times less,respectively;annual runoff was 3.5 mm,reduced by 79.1%;annual soil loss was 10.1 t·km^-2,reduced by 95%which was far below the value of soil loss tolerance(200 t·km^-2)fo blacksoil in Northeast China.Compared with CT,the soil water storages in 0¹50 cm soil layer had no significant difference in PTS;soil initial infiltration rate in 0¹0 cm soil layer were higher in PTS,increased by 20%;the number of annual surface runoff and soil loss in the PTS were 3 times and 2 times less,respectively;annual runoff and soil loss was 5.9 mm and 23.5 t·km^-2,reduced by66.1%and 89.4%,respectively These results indicated both NTS and PTS had better capacity in soil and water conservation,besides the result of NTS was superior to PTS.As NTS and PTS were affected by the environmental factors,the straw decomposition rate and the release rates of nutrient element in straw were different between NTS and PTS.After 1 year,the returning corn straw decomposition rate of NTS and PTS was 54.5%and 70.1%,respectively.That was because the effect of water-heat environment on straw was different after straw returning in NTS and PTS.As the straw in NTS was on soil surface,the soil temperature was higher and soil water content was lower?except the rainfall season?around the straw.While the straw in PTS was bound by soil,the value of soil water content was mostly more than 30%and the soil temperature was lower than NTS.Compared with NTS,the decomposition rates of cellulose,hemicellulose and lignin in PTS was increased by12.5%,8.6%and 6.2%,respectively;the release rates of carbon,nitrogen,phosphorus and potassium in PTS was increased by 17.0%,12.2%,10.6%and 7.3%,respectively.Thus it was easier to decompose the corn straw and release the nutrient element in PTS than NTS.Both NTS and PTS could increase the soil nutrient in arable layer and improve the soil structure.Compared with CT,the content of soil organic matter,total nitrogen,total phosphorus and total potassium in 0¹0 cm soil layer were increased by 16.3%,18.5%,26.2%and 7.7%in NTS,respectively;the content of soil organic matter and total nitrogen in 10²0 cm soil layer was also increased in PTS.The content of soil nutrient in 0¹0 cm soil layer has no difference between PTS and CT,while PTS could increase the content of soil organic matter by 52.6%,total nitrogen by 99.5%,total phosphorus by 62.7%and total potassium by 25.9%in 10³0 cm soil layer.There was no difference on the value of soil bulk density and soil porosity in 0¹0 cm soil layer between CT and NTS.However,compared with CT,NTS could decrease the R value of three-phase ratio of soil and promote the formation and stabilization of soil aggregates in 0¹0 cm soil layer;the value of R_0.25,MWD and GWD was increased by 10.7%,43.4%and 18.8%,respectively.There was no significant difference on the value of soil bulk density,soil porosity,R value of three-phase ratio and stabilization of soil aggregates in soil surface between PTS and CT,while the soil non-capillary porosity in soil surface was increased by PTS.PTS also promoted the formation of soil aggregates and increased the stabilization of soil aggregates in10³0 cm soil layer compared with CT.Therefore both NTS and PTS could increase soil nutrient,promote the formation of soil aggregates and improve the soil structure by total straw returning.The above result of study indicated that both NTS and PTS had positive effect on soil and water conservation and soil quality recovery.Although the effect of PTS on soil and water conservation was weaker than NTS,compared with NTS,the decomposition rate and nutrient release rate of con straw were faster in PTS;the soil pore structure and fertility in“plow pan”were improved in PTS;the soil infiltration properties was also increased in PTS;the essential nutrients for crop growth was provided in PTS,which was benefit to increasing the crop yield.Both NTS and PTS has positive effect on soil and water conservation,thus these two straw returning method are worth popularization and application in sloping farmland in Northeast China.