Influences Of Long-term Fertilization And Tillage On Soil Fertility In Sloping Farmland Of Purple Soil Under Natural Rainfall

Purple soil,is one of the main agricultural planting soil,found mostly in the sloply farmland of the Three Gorges reservoir area.However,because of prolonged use of the artificial fertilizers cultivation practices,the purple soil are exposed to the varying degree of soil fertility deterioration.With the occurrence of farmland surface runoff from sloping arable land caused by natural rainfall,non-point source pollution has seriously affected the ecological and economic development of the Three Gorges reservoir area.Therefore,through the analysis of the evolution process of soil nutrients and the evaluation of comprehensive fertility,it can scientifically guide the management of fertilization and the selection of farming systems for sloping cultivated land on purple soil and promote the sustainable development of ecological agriculture.This paper is based on the long-term test of surface runoff monitoring non point pollution from hills in the southern mountainous areas under the Ministry of Agriculture,This experiment design consists of five kinds of experimental treatment(CK,combined application of manure and fertilizer(T1),chemical fertilization(T2),chemical fertilizer with double fertilization(T3),contour plowing of chemical fertilizer(T4)).We analyzed and measured fertility indicators such as soil organic matter,total nitrogen,total phosphorus,total potassium,available phosphorus,nitrate nitrogen,and ammonium nitrogen.Using the grey correlation method and the Nemerow index analysis method,we established an evaluation index system for soil fertility quality,and comprehensively evaluated the soil fertility characteristics under different fertilization modes and tillage modes,combined with years of surface runoff under natural rainfall conditions.The main results are as follows:(1)The surface runoff is influenced by many factors on the sloping farmland of purple soil.It mainly includes hydrological factors,fertilization patterns and farming methods.Based on the long-term natural rainfall monitoring cell,the interannual variation is in a logarithmic relationship with annual runoff,y=-aln(x)+b,(where R~2ranges from 0.2813 to 0.6754);The relationship between the average annual runoff size followed by CK(1332.97 mm)>T3(1038.40 mm)>T2(1010.19 mm)>TI(955.93mm)>T4(752.57 mm).Moreover,the change of nitrogen and phosphorus loss in runoff of purple soil slopes has a significant relationship with the level of fertilization.(2)The soil nutrient content of the soil was changed in different degrees under the system of maize and wheat rotation in the purple soil slope farmland with long-term location fertilization.Comparison with the first year and last year of the experiment,for the entire test plot,The total content of soil organic matter decreased by 6.97%,the total nitrate nitrogen content decreased by 45.43%,the total content of ammonium nitrogen decreased by 70.53%,the total nitrogen content decreased by 37.72%,total phosphorus content decreased by 40.08%overall,the total available phosphorus content decreased by 33.60%.The total potassium content decreased by 34.31%overall.The contents of ammonium nitrogen and nitrate nitrogen in soil decreased the most,and the content of soil organic matter decreased the least.(3)The nutrient indicators showed that the soil nutrient holding effect of the single slope and cross-ridge ridge cultivation was the best.Under the same fertilization mode,the tillage method is an important factor that affects the change of soil nutrients.Under all sloping tillage,the change of soil nutrient index is different because of the different fertilization patterns.Among them,soil organic matter,total phosphorus and total nitrogen content were optimal in mixed treatment of chemical fertilizer and farmyard manure.Soil nitrate nitrogen,ammonium nitrogen and total potassium content were the smallest under increment fertilizer treatment.Soil available phosphorus content was most in soil under optimized fertilization.(4)Through gray correlation analysis of each index of soil fertility,cross slope cultivation in chemical fertilizer treatment(0.643)showed the highest correlation value,followed by downslope tillage optimized fertilization(0.627),downslope tillage fertilizer incremental processing(0.625),downslope tillage fertilizer and farmyard manure(0.594),CK treatment(0.550).In the 9 year monitoring test,the correlation of CK was reduced by 42.11%,T1 was reduced by 24.15%,T2 was reduced by 34.01%,T3 was reduced by 27.87%,and T4 was reduced by 35.95%.The average annual runoff and annual average correlation degree satisfy a linear function model(y=-0.0002x+0.7628).(5)Through the analysis of the Nemero index of the soil fertility indicators,the soil quality index under single-fertilizer treatment with cross-slope cultivation(1.00)was the largest,followed by chemical fertilizer with double fertilization treatment(0.94),the treatment of combined application of manure and fertilizer(0.92),the single-fertilizer treatment(0.91)and control treatment(0.75).Under the 9-year monitoring test,the T1's quality index decreased by 19.43%,T2's decreased by 27.89%,T3's decreased by27.25%,T4's decreased by 31.78%,and CK's decreased by 47.25%.