Effects Of Long-term Fertilization On Soil Quality And Farmland System Sustainability On Sloping Farmland In Loess Hilly Region

Focused on the scientific problem of soil quality evolution and realistic requirement for sustainable developmen on sloping farmland in the Loess Hilly Region,a 34-year long-term fertilization experiment on the sloping farmland was studied in the Zhifanggou watershed in Ansai County,Shaanxi Province.The fertilization treatments included CK(no fertilizer control),N(single application of N fertilizer),P(single application of P fertilizer),NP(combined application of N and P fertilizer),M(single application of organic fertilizer),MN(combined application of organic fertilizer and N fertilizer),and MNP(combined application of organic fertilizer with N and P fertilizer).The evolution trend of soil quality indicators and the crop properties were studied based on the 34-year historical data and field site sampling of long-term located fertilization test.Meanwhile,taken the characteristics of soil quality evolution of terrace soil under long-term fertilization in this area as a control,explored the driving force of soil quality evolution in sloping farmland with the effect of erosion and fertilization,and analyzed the sensitivity of different soil indicators and the key restrictive soil quality factor.In order to evaluate the sustainability of farmland system in sloping farmland under long-term fertilization,synthesized soil nutrient index,biological index and crop index and calculated the sustainability index of the system under different fertilization treatments based on the triangle area method,provided basis for rational fertilization,soil conservation and management on sloping farmland in the Loess Hilly Region,and promoted sustainable agricultural development.The main conclusions were as follows:1.Compared with the control,long-term application of organic fertilizer and combined application of N and P fertilizer could increase soil nutrient content,improve soil biological environment and soil structure,and single application of N and P fertilizer would lead to degradation of soil quality.After 34-year long-term application of organic fertilizer and combined application of N and P fertilizer,soil organic matter,total N,alkali-hydrolyzable N,available P,and available K increased by 1.12%~31.81%,16.96%~40.74%,23.34%~53.95%,2.04%~106.60%,20.81%~41.28%,respectively,soil enzyme activities and microbial biomass C,N,and P contents increased by 20.87%~70.55% and 24.20%~121.77%;The combination of N and P fertilizer and application of organic fertilizer increased the content of aggregates >2mm by 2.77%~76.17%;The content of soil organic matter,total N,available P,and available K in the single application of N fertilizer decreased by 14.97%,2.71%,25.13%,and 14.38%,respectively,the content of soil water-stable aggregates in the single application of N fertilizer and P fertilizer decreased by 2.04% and 0.66%,respectively.2.During long-term fertilization on sloping farmland,soil organic matter,total N,and alkali-hydrolyzable N content showed an increasing trend,and soil total P,available P,and available K were not significantly increased.After 34-year long-term fertilization,the contents of soil organic matter,total N,and alkali-hydrolyzable N increased by 36.0% ~110.8%,9.2%~37.5%,and 11.4%~39.0%,respectively,and the growth rates were 0.04~0.13g/(kg·a),0.0011~0.0043 g/(kg·a),0.08~0.27mg/(kg·a),the growth rate was less than the growth rate of soil quality indicators after fertilizing terrace soil in the area.3.Fertilization could improve the status of N and P nutrition in crops on sloping farmland,single application of N fertilizer and single application of P fertilizer had the best effect on increasing N and P contents in various organs of crop.Long-term fertilization could increase crop bio-production and economic yield,organic fertilizer had a greater effect than chemical fertilization,combined application of organic fertilizer with N and P fertilizer had the best effect.Although the soil nutrient and structural status of sloping farmland continued to improve under long-term fertilization,under the current fertilization and farmland management measures,the crop yield on the sloping farmland in the study area had reached a maximum and tended to be stable.4.The growth rate of soil microbial biomass C and N content under long-term fertilization was greater than that of soil and crop C and N content,it was more sensitive to fertilization.Total P content in soil increased slightly,but the microbial biomass P and crop total P contents increased significantly,the growth rate of total P content in crop stem was the highest,more sensitive to fertilization.After 34-year long-term fertilization,soil and microbial biomass P content in the Loess Hilly Region was relatively abundant,C and N content was relatively low,resulting in low soil and microbial biomass C: N and C: P,therefore,it was necessary to pay attention to the input of organic fertilizer on the sloping farmland in this area.The change of soil stoichiometry had a significant effect on the ratio of crop stem elements,and no significant effect on the stoichiometric ratio of microbial elements.5.Long-term application of organic fertilizers(M,MN,and MNP)on sloping farmland in Loess Hilly Region in northern Shaanxi could make the farmland system sustainable,while the long-term application of chemical fertilizers(N,P,NP)in farmland system was not sustainable.Under the combined application of organic fertilizer with N and P fertilizer(that is,500 kg/mu organic fertilizer,N 7.6 kg/mu,and P 16 kg/mu per year),soil quality index,nutrient index,biological index,crop index,and sustainability index were respectively increased 43.46%,33.54%,66.40%,411.07%,and 352.13%,which was the recommended fertilization treatment for sloping farmland in the study area.