Effects Of Straw Returning On The Characteristics Of Soil Fertility And Nitrogen Fate In Wheat-maize Rotation System In The Hilly Area Of Sichuan Basin

Straw plays an important role in nutrient cycling and energy exchange in ecosystems,the reasonable amount and way of straw returning to the field will be positive to relief the environment pollution and reduce the agricultural waste.It is also conducive to soil fertility and sustainable development of agriculture.This research focused on the effects of straw recycling on soil fertility and nitrogen use efficiency of crop-soil system by recycling amounts and returning ways in the hilly area of central Sichuan Basin under winter wheat-summer maize rotation system.The experimental site is in Yanting Agro-ecological Experimental Station of Purple Soil,Chinese Academy of Science.We set six treatments:maize-wheat-0%straw returning?CK?;maize-wheat-30%straw returning(RMW₃₀);maize-wheat-50%straw returning(RMW₅₀);maize-wheat-100%straw returning(RMW₁₀₀);maize-wheat-cutted returning(RMW_cut)and maize-wheat-burned returning(RMW_burn),representing different straw recycling amount and ways.By analyzing the crop productions,soil physical properties,soil nutrient characteristics,soil fauna dietary habits and the nitrogen?N?fate under different treatments,which aims to find out the reasonable amount and way of returning straw to the field which would be beneficial to the soil structure and fertility in the hilly areas of central Sichuan,furthermore,which would be conducive to sustainable agricultural and environmentally friendly.The main conclusions were as follows:1.Returning straw to the field has effectively improved crop productivity,but there is no positive line correlation between the returning amount and crop productivity.The yields of wheat and maize in RMW₃₀ were 3854 and 6464 kg ha^-1,respectively,which were higher than other treatments,and there was no significant difference among treatments.The wheat yield of RMW₁₀₀is 15.5%lower than RMW₃₀ and lower than that of CK.There was no significant difference on biomass among different returning amount of straw.The biomass of wheat under RMW₅₀ is 12309kg ha^-1,higher than those of other treatments,and the higher biomass of maize season was from RMW₁₀₀treatment which was 14442 kg ha^-1.There was no significant effect on productivity of the straw returning way to the field.The biomass and yield of RMW_cut in the wheat season were higher,and RMW_burn in the maize season was higher.2.Returning straw improved soil physical structure.The soil bulk density of RMW₃₀and RMW₅₀was significantly lower than CK,and the saturated hydraulic conductivity of RMW₁₀₀ increased significantly and to be 1.6 mm min^-1,the porosity of RMW₃₀?RMW₅₀and RMW₁₀₀ were 8.4%?6.2%and 1.7%higher than CK,respectively.The pore features of RMW₃₀ was reasonable matching and good connectivity,which beneficial to improve the soil structure and quality.Throat cross-sectional area,coordination number,roundness and pore connectivity of RMW₅₀ were the lowest,RMW₁₀₀ are the highest,pore diameter tends to be larger.There were no significant differences in the soil bulk density,saturated water content,and saturated hydraulic conductivity of the straw returning ways.The soil moisture content of RMW_cut soil was significantly higher than CK treatment,and the soil moisture content of 30-50cm in RMW_burn treatment was significantly reduced by only 17.6%.The pore?>1000?m?volume ratio of CK and RMW_burn was 86.8%and91.3%,and RMW_cutwas 50%,so the pore diameter tended to be smaller.RMW_cuthas higher porosity than other treatments,and made the pores reasonable matching.There is no significant difference in pore structure between RMW_burnand CK treatments.3.There was no significant difference in p H under different returning amount.The contents of nutrient increased with the returning amount of straw.The SOM and AN content of wheat season in RMW₁₀₀ were significantly higher than CK treatment.Compared with CK,increased by 18.46 mg kg^-1 and 5.3 g kg^-1,respectively.Except for AP in the maize season,there were no significant differences among other treatments.There were no significant differences in p H and AP content of the straw return ways.The organic matter content of the RMW_cut and RMW_burn in wheat season was higher than CK treatment at 5.2 and 3.1 g kg^-1,respectively,and the RMW_cut was significantly higher than the CK treatment.AN content in wheat season and maize season under RMW_cuttreatment were up to 76.3 and 80.5 mg kg^-1,respectively.4.Abundant omnivorous soil animal species and larger amount has been found in this study district,and the number of predatory and saprophytic soil animals is small,and the species is single.The amount of omnivorous soil animals in RMW₃₀ can reach 38,000 m^-2,which is significantly higher than RMW₅₀ treatment.There are 4 species of phytophagous soil animals can be identified in CK treatment,with a total number of 2,500 m^-2,and only 1-2 species in other treatments,and the RMW₅₀treatment lacks this.RMW₁₀₀ has increased the amount of saprophytic and predatory soil animals to 5,000 m^-2.Abundant phytophagous soil animal species and amount in CK.The omnivorous soil animals of RMW_burn was significantly higher than other treatments,and there was no significant difference in species.The surface layer of RMW_burn predatory soil animals was lacking and accumulated in the deeper layers.5.In different treatments of returning straw to the field,nitrogen fertilizer is the main source of N input accounting for 70%,straw accounting for 20%,nitrogen deposition accounting for 5%-7%;seed nitrogen accounts for only 1%.Nitrogen efficiency of RMW₃₀in wheat seasonal is the highest is up to 53.1%,and the N output is mainly carried out by crops,accounts for 80%-90%of the total output.Nitrogen surplus was shown in all treatment of wheat season,and the surplus was positively correlated with the amount of straw returning.Nitrogen efficiency increase with the rise of straw amount in maize season,and the proportion of soil leaching loss is high,the gaseous accounts for a relatively small amount.N balance surplus amount in CK?RMW₅₀ and RMW₁₀₀ is-97?-76 and 15kg ha^-1.Compared with CK,RMW_cut and RMW_burn both improved the efficiency of nitrogen,and there was no significant difference between treatments.Nitrogen surplus appeared in all treatments in wheat seasons.RMW_cut treatment surplus was up to 45.1 kg ha^-1,and the other treatments were about 26 kg ha^-1.Depletion of soil nitrogen occurred in each treatment in maize season,and the minimum surplus of straw CK was-97.1 kg ha^-1.In summary,the RMW₃₀ in wheat season and the RMW₁₀₀in maize season,which can make the crop maintain high productivity and high nitrogen efficiency,improve the soil physical structure and soil fertility,increase the species abundance of soil animals,and be more achieve sustainable development of agriculture.Nitrogen Surplus phenomenon in both of treatments had mentioned Therefore,in the actual agricultural production,the amount of fertilizer can be reduced.Straw burning also field due to high temperature roasting,easy to destroy the soil structure,but straw cutted to field is more conducive to improving crop yield and soil structure,play a water conservation and fertilizer effect,so in the hilly area of Sichuan basin recommended the straw cutted returning to the field.