Effect Of Disturbance Surface On Soil Nutrient Loss Under Different Slope Length

In recent years, the human engineering activity in Chongqing is frequent, such as the development of agriculture and forestry, municipal construction, land clearing and so on. These mankind activities caused severe disturbance to the earth’s surface, and lead to surface loose and exposed, the situation of soil and water loss is not optimistic. In addition, the changes of slope length lead to the change of collect-water quantity and thus affect the current form. At the same time, the increase of runoff lead to the increase of runoff depth at slope down, so reduced the raindrop splash erosion ability. So the effect of different slope length on the soil erosion process is also different. So researching the effect of disturbance surface on soil nutrient loss under different slope lengths has important guiding significance for prevention and control of soil and water loss of disturbance surface by human activity, such as the development of agriculture and forestry, land clearing and so on. In this paper, through experiments in runoff plots, effects of disturbance surface on soil nutrient loss under three different slope lengths of20,40and60m were studied under the condition of natural rainfall, so as to provide reference for preventing soil degradation and formulating control measures of disturbance surface by human activity in the future. The results showed that:(l)For rainfall runoff and erosion sediment loads of different treatments, the per unit area rainfall change law of different treatments with the rainfall is basically the same. For the same rainfall and slope length, the per unit area runoff of disturbance surface treatments were obviously greater than that of the natural slope treatments. Comparing the different slope length treatments, both of the per unit area runoff of the disturbance surface treatments and that of the natural slope surface treatments were all reducing with the increase of slope length when the rainfall is less than50mm. The change law of per unit area sediment loss with rainfall is basically same as the change law of per unit area runoff. For the natural slope surface treatments, the relationship between the unit area sediment loss and the unit area runoff meet the second order polynomial function relation. For the disturbance surface treatments, the relationship between the unit area sediment loss and the unit area runoff meet the exponential function relationship y=ae x, a>0, b>0or the power function relationship y=axb, a>0, b>0.(2)For the loss quantity of nitrogen and phosphorus in rainfall runoff, the loss quantity of nitrogen and phosphorus in rainfall runoff of different treatments meet ups and downs fluctuation changes with the increase of rainfall when the rainfall is less than51.4mm, and in addition to the individual value,the change tendency is not obvious. The loss quantity of nitrogen and phosphorus in rainfall runoff of different treatments were increased with the increase of rainfall, and the change tendency is obvious. In addition, the loss quantity of nitrogen and phosphorus in rainfall runoff of the disturbance surface treatments were obviously higher than that of natural slope surface treatments under the same slope length.(3)For the total nutrient losses in runoff, artificial disturbance surface obviously increased the nutrient losses by runoff. Through analysis of variance, both of the total loss of nitrogen and phosphorus by runoff of the disturbance surface treatments were significantly higher than that of natural slope treatments under the same slope length (a=0.05). Comparing the different slope length treatments, the total loss of nitrogen by runoff was reduced with the increase of slope length for both of the disturbance surface treatments and natural slope treatments, and the difference of the total loss of the four kinds of forms nitrogen in runoff of the disturbance surface treatments between different slope length all reached significant level (a=0.05).But for the total loss of phosphorus in runoff, it is showed that the total loss is highest in20m slope length treatments, the second is60m lope length treatments, the minimum is40m lope length treatments. What is more, the total loss of phosphorus in runoff of the disturbance surface treatments at the20m slope length was significantly greater than that of the40m and60m slope length treatments. But there has no significant difference between that of40m slope length treatments and60m slope length treatments (a=0.05)(4)For the change amount of surface soil nutrient content in different treatments, the change amount of surface soil nutrient content in the disturbance surface treatments was obviously higher than that of natural slope treatments under the same slope length. What is more, in addition to the total potassium in soil, the difference of the change amount of other kinds of surface soil nutrient content reached significant level (a=0.05) between the disturbance surface treatments and natural slope surface treatments. This showed that human disturbance surface increase the loss of surface soil nutrient. Comparing the different slope length treatments, the change amount of surface soil nutrient content in both of the disturbance surface treatments and natural slope surface treatments all was reduced with the increase of slope length, and in addition to the soil available potassium, the change amount of other kinds of surface soil nutrient content in both of the disturbance surface treatments and natural slope surface treatments under the 20m slope length was significantly higher than that of40m and60m slope length plots (a=0.05).(5)For the nutrient loss amount of by sediment of different treatments, the nutrient loss amount of by sediment of the disturbance surface treatments was significantly higher than that of the natural slope surface treatments under the same slope length (a=0.05). Comparing the different slope length treatments, both the nutrient loss amount of by sediment of the disturbance surface treatments and natural slope surface treatments all was reduced with the increase of slope length. What is more, both the nutrient loss amount of by sediment of the disturbance surface treatments and natural slope surface treatments under the20m slope length was significantly higher than that of40m and60m slope length plots (a=0.05), but the difference of the nutrient loss amount of by sediment between40m slope length treatments and60m slope length treatments was small. In addition, the potassium loss amount of by sediment was obviously higher than that of nitrogen and phosphorus.(6) Comparing the loss total loss amount of nitrogen and phosphorus in runoff and sediment, The results showed that the difference of the total loss amount of nitrogen and phosphorus in runoff and sediment between different treatments was fairly obvious. Among them, the total loss amount of total nitrogen in runoff and sediment varied from0.0396kg·hm-2·a to2.0772kg·hm-2·a, the total loss amount of total phosphorus in runoff and sediment varied from0.0101kg·hm-2·a to0.7929kg·hm-2·a, and the total loss amount of nitrogen and phosphorus in runoff and sediment of the disturbance surface treatments was obviously higher than that of the natural slope surface treatments. What is more, for the disturbance surface treatments, more than80%of the loss amount of nitrogen and phosphorus in soil was from sediment, so the sediment is the main way of nitrogen and phosphorus loss. Bur for the natural slope surface treatments, the main way of soil nitrogen and phosphorus loss is also influenced by the slope length. In general, the soil total nitrogen loss was mainly along with runoff, the soil total phosphorus loss was mainly along with sediment. This showed that human disturbance surface not only increased the soil nutrient loss with runoff and sediment, but also has important influence on the way of soil nutrient loss.