| This study was taken the farmland in loess tableland area as the research object, around ed the rainfall process and soil nutrient loss and based on the artificial rainfall simulation to analyses the characteristics of soil and water loss and nitrogen and phosphorus nutrient loss and the influence on soil water deep infiltration, nutrient vertical distribution characteristics and of vertical dynamic changes of soil moisture under different influence factors(slope, the early stage of the rainfall intensity, soil water content, soil conditioner PAM).The main results were as follows:The experimental sample is Dark loessial soils in five slopes as 5°, 10°, 15°, 20° and 25° gradients. The results showed that under the constant rainfall intensity the runoff and sediment yield increased rapidly within the initial 10 minutes then increased slowly and gradually stabilized and the order of output flow was 15°, 10°, 20°, 5° and 25°; total sediment yield of 10° was maximum, 15 ° and 20 ° of the total sediment yield was similar, 5 ° and 25 ° of the total sediment yield was close. Under the conditions of different slopes, the trend with the slope of total runoff and total sediment yield can be fitted with a quadratic function and the correlation coefficient R2 =0.65. And there was a critical value that had a significant effect on nutrient concentrations of runoff under slope degrees between 10° and 15°. In addition the migration process of nitrate nitrogen in wet layer could be described in the power function and the concentration change of ammonium nitrogen in wet layer was in agreement with cubic polynomial curve; while there was no significant change of the available P concentration with depth under the wet layer. The trend with the slope of the total loss amount of nitrate and ammonium ware quadratic polynomial change, the correlation coefficient R2 of 0.91 and 0.77 respectively. The total amount of water-soluble phosphorus loss maximum on 20 °, it was 1.61 times of 15 ° slope.Initial nutrient concentration in runoff influenced mainly by nutrient solubility and the quantity of soil loss had more effect on the nutrient concentration in the late runoff.Impacts of rainfall intensity on soil erosion and nitrogen and phosphorus loss under 0.7 mm·min-1, 1.2mm·min-1, 1.7 mm·min-1and 1.9 mm·min-1 levers on dark loessial soils in gully region of the Loess Plateau were studied under the artificial rain experiments. The results showed: ①Total runoff increased with the increase of rainfall intensity; when the rainfall intensity was 0.7 mm·min-1and 1.2mm·min-1, the stable flow rate, average runoff depth, total runoff and total sediment had no significant difference; When the rainfall intensity was 1.7 mm·min-1, the total sediment was the largest. ②When the rainfall intensity was 0.7 mm·min-1, 1.2mm·min-1, and 1.9 mm·min-1, nitrogen and phosphorus loss process was consistent and tended to be stable after slowly reduced first in the process of rainfall; When the rainfall intensity was 1.7 mm·min-1, water soluble phosphorus, nitrate nitrogen and ammonium nitrogen concentrations were significantly higher than which under the other three rainfall intensity(p<0.05), the trend with the runoff time of water soluble phosphorus concentration could be fitted with a quadratic polynomial and the correlation coefficient R2 =0.93, and the trend of nitrate nitrogen and ammonium nitrogen concentration could be fitted with a logarithmic function and the correlation coefficient R2 >0.8. ③Total loss of phosphorus and nitrate increased with the increase of rainfall intensity, and total loss of ammonium nitrogen was maximum when the rainfall intensity was 1.7 mm·min-1. ④The depth of the migration of phosphorus was not affected by the change rainfall intensity, migration depth of nitrate nitrogen increased with the increase of rainfall intensity; In the 1.7 mm·min-1, phosphorus, nitrate nitrogen and ammonium nitrogen were lowest in the soil vertical section, three kinds of solute loss and largest downward leaching at least.The results of soil erosion and nutrient loss under five different antecedent soil moisture levers of 5%, 9%, 13%, 17% and 20% showed that the time of slope reaching stable infiltration and the stable runoff-yielding decreased with the increasing of soil moisture content when under the same rainfall intensity and slope. In addition, the amount of runoff and sediment yield increased with the antecedent soil moisture increasing between 5% and 17% but it diminished between 17% and 20%. There is a significant linear relationship between the amount of sediment yield and runoff yield, and the coefficient is 0.889. The total loss of soluble phosphorus, nitrate nitrogen and ammonium nitrogen and their concentration were the largest when antecedent soil moisture was 17%. And three kinds of nutrient accumulation decreased with the increasing of water content in moist layer. Therefore, we believed 17% of antecedent soil moisture was a critical value to affect nutrient concentration changes in runoff. There is little amount of nutrient loss and it changed small under antecedent soil moisture between 5% and 9%. The largest average amount of nutrient loss is soluble phosphorus; it is 1.32 and 2.46 times than nitrate nitrogen and ammonium nitrogen, respectively.Impacts of PAM on soil erosion and nitrogen and phosphorus loss under 5 °, 15 ° and 25 ° slopes on dark loessial soils in gully region of the Loess Plateau were studied under the artificial rain experiments. The results showed: ①After applying PAM, the total runoff of 5° and 15° were increased but on 25° slope was reduced; initial sediment yield was bigger in the PAM group, and 8 min later sediment yield rate started to reduce and there were significant differences between PAM group and the control group. This indicated that work time of PAM was started about 8 to 10 minutes later or so, and the sediment reduction rate of three slope(5°, 15°, 25°)were 38.2%, 3.7% and 53.9%, respectively. ②In PAM group, concentration of phosphorus on all three slope were reduced and it was not affected by the change of slope; for the 5 °and 15 ° slope, the effect of PAM on ammonium nitrogen concentration was not obvious, but the ammonium nitrogen concentration of 25°slope was reduced significantly; In addition, the application of PAM could reduce the initial concentration of ammonium nitrogen. ③PAM could affect the moisture redistribution process and reduced the downward leaching of nitrate nitrogen and phosphorus of all three slopes(5°, 15°and 25°). ④After applying PAM, the total phosphorus loss of 5 °, 15° and 25° slope were decreased and the amplitude was 77.6%, 64.5% and 85.1% respectively; Total nitrate nitrogen loss was increased with the increase of slope first and then decreased, and there was a twist slope between 15 ° ~ 20 ° slope that could change the effect of PAM on nitrate nitrogen; In PAM group, nitrate nitrogen loss was significant correlation with runoff at the 0.05 level, the correlation coefficient was 0.998; PAM could reduce dissolved ammonia nitrogen loss of 25 ° slope significantly, the reduce amplitude was 60.1%. |
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