| Taking slope farmland in purple hilly as object, this paper sets up four treatments CK(no-improvement practice),BC(bio-char addition alone),PAM(application of polyacrylamide on the soil surface) and SM(maize straw addition) in the standard plots, analyzing the effect of different treatments on the soil physicochemical properties from soil structure, infiltration and nutrient by the method of physicochemical analysis, on soil erosion from runoff and sediment, on nutrient loss, and on biomass. In addition, the effect of rainfall factors on runoff and sediment, the relationship between nutrient loss and runoff was analyzed through grey relational analysis and regression analysis, respectively. Finally, this paper researched on the effect of soil structure and nutrient on biomass by regression analysis. Results can provide effective theoretical basis for the selection of farmland protection measures in purple hilly area. The main conclusions are as follows:(1)There was great difference in the effect of different conservation tillage measures on soil structure. Especially for 0-10 cm,soil bulk density was in the order of CK(1.24g/cm3)>BC(1.18g/cm3)>PAM(1.13g/cm3)>SM(1.11g/cm3),and soil porosity was opposite. soil aggregates in the studied area were mainly in the size >5mm and 5-2mm,and soil aggregate(>0.25mm) was in the order of SM>PAM>BC>CK, in which difference among treatments decreased with the soil depth. MWD of soil aggregates of different treatments decreased with the soil depth, which was in the order of SM>PAM>BC>CK, while soil aggregate fractal dimension was opposite to MWD. The organic carbon of soil aggregates had great difference in aggregate size, which was the highest at 0.5—0.25 mm. Within the 0-30 cm soil depth, the average content of organic carbon in soil aggregates was in the order of SM >PAM >BC >CK, and decreased with the soil depth.(2) There was great difference in the effect of different conservation tillage measures on soil infiltration. The infiltration of each treatment had experienced three stages for strong-weak-stability, and decreased with the time increasing until keeping stable. In 0-30 cm soil layer, soil infiltration capacity decreased with the soil depth,which was in the order o f SM>PAM>BC>CK. In 0-10 cm soil layer, soil infiltration capacity was the strongest. w hich the initial infiltration rate and stable infiltration rate of SM, PAM, BC, CK were 53.77/32.31mm/min, 33.97/20.08mm/min, 18.77/9.48mm/min, 8.92/5.76mm/min, respectively. Soil structure w-as poor with the soil depth, which leaded to the weak infiltration capacity.(3) There was great difference in the effect of different conservation tillage measures on runoff and sediment. There is obvious difference in sediment when rainfall was 8.9—39.7mm and rainfall type was moderate or heavy rain, but not obvious when the rainfall was above 47.6mm and the rainfall intensity was up to rainstorm, which indicated measures had a great effect on flow and sediment reduction only when rainfall and rainfall intensity was in a range, while the effect would become low obviously when rainfall and rainfall intensity was up to a certain value. Total runoff was in the order of CK(7.20L/m2)>BC(6.00L/m2)>PAM(5.22L/m2)>SM(4.75L/m2),and total sediment CK(0.108kg/m2)>BC(0.091kg/m2)>PAM(0.084kg/m2)>SM(0.075kg/m2).The grey correlation analysis showed that the rainfall factors which influenced the runoff were mainly rainfall for CK and BC, and maximum rainfall intensity for PAM and SM. While the factor which influenced sediment was rainfall intensity. Regression analysis showed that there was a very significant exponential function relation between runoff(y) and rainfall(x)(y=axb, a, b was coefficient), and a very significant power function relation between sediment(y) and runoff(x)(y=axb, a, b was coefficient). These models could predict variations of runoff and sediment, which provided scientific evidence for assessing the risk of soil and water loss of slope farmland in purple soil area.(4) Total nitrogen and hydrolytic nitrogen concentration of runoff were 1.686—10.829mg/L and 1.047—5.234mg/L, respectively. The phosphorus concentration in runoff was significantly less than nitrogen, which total phosphorus and water soluble phosphorus concentration were 0.330—4.873mg/L and 0.220—4.768mg/L, respectively. Total nitrogen loss during the test was in the order of CK(4018.61 mg/100m2)>BC(3638.49 mg/100m2)>PAM(2708.85mg/100m2)>SM(2285.32 mg/100m2),and hydrolytic nitrogen in the order of CK(2029.36mg/100m2)>BC(1441.28mg/100m2)>PAM(1169.27mg/100m2)>SM(964.44mg/100m2). Total phosphorus loss was in the order of BC( 1058.6 mg/100m2) > PAM( 1045.51mg/100m2) > CK(961.73mg/100m2)>SM(662.39 mg/100m2),and water soluble phosphorus loss in the order of PAM(871.88 mg/100m2)>BC(864.77mg/100m2)>CK(787.26mg/100m2)>SM(496.05mg/100m2), in which there was significant difference between SM and other treatments. The regression analysis showed that there was a very significant exponential function relationship between the nutrient loss and runoff for CK, a very significant two curves relationship between total nitrogen, hydrolysis nitrogen loss and runoff for BC and SM, and a very significant power function relationship between Total phosphorus and soluble phosphorus loss for BC, SM and nutrient loss for PAM and runoff. These models could predict variation of nutrient loss, which provided scientific evidence for assessing the risk of non-point source pollution in the Three Gorges area.(5) Different treatments had obvious effect on increasing biomass. Regression analysis showed that there was significant or very significant linear relationship between biomass and MWD, fractal dimension, organic carbon, total nitrogen, hydrolytic nitrogen, but not between biomass and the total phosphorus and soluble phosphorus. The regression equation reflected the relationship between crop yield and soil structure, nutrient, which could predict crop yield by changes of soil structure and nutrient content.(6) Based on soil physicochemical property improvement, runoff and sediment reduction, nutrient controlling and crop yield creasing, SM was more efficient than others, which indicated SM had better suitability for slope farmland in purple soil as an important agricultural measure. |
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