Study On The Soil Erosion And Nutrient Loss From Gneiss Mountainous Area Under Different Underlying Surface

Soil erosion in sloping land is a serious ecological problem of our country. Theproportion of mountainous area in Hebei Province is67%, Taihang Mountain belongs tothe northern mountainous area. It is one of the more serious soil erosion areas, of whichsoil texture and other factors have big difference with other regions, so it is necessary forthis area to research soil erosion. A artificial simulated rainfall device is used in this studyto research the effects of different underlying surfaces(land utilization, sloping surface anddifferent growth stages of crops)on soil and nutrient loss in gneiss sloping and has certainsignificance to the control of soil erosion in mountainous ecosystems and sloping land andnon-point source pollution of small watersheds. The main conclusions were as follows:1. Runoff-yielding time decreased with increasing slopes. There are differences insediment yield and runoff situation in Gneiss slope under different surface conditionsUnder different treatments, the runoff time、runoff、runoff coefficient and runoff-yieldingtend： fertilizing slope<compaction slope <farming slope. There is a clear exponentialrelationship between sediment yield and runoff. Runoff intensity increases with rainfallduration after becoming the most value,then reaches stable.Sediment production rateshows a decreasing trend over time, to a certain extent,reducing until no change; overlandflow stability at different times, compaction slope significantly lags behind the fertilizerand farming. The total amount of different nutrient loss show K> N> P; under differentslope nutrient loss is mainly in the form of sediment combination state especially for P andK, N loss are both of sediment and dissolved state, dissolved nitrogen in nitrate lossesaccounted for55%, ammonia15%～17%. P in sediment is mainly composed by organicphosphorus; runoff is significantly negatively correlated to nutrient loss, the larger theamount of runoff,the greater the amount of N、P、K loss.Between the amount of runoffand sediment yield and nutrient loss have a close relationship, but the total phosphoruscontent and phosphorus loss is no obvious correlation.2．There is a different runoff time under different land use patterns, as well as thesteady flow time. The steady time of grass and millet are significantly later than the bare.Runoff, runoff coefficient and sediment yield of bare land were the biggest in threedifferent land use patterns, the smallest is the grass land. The sediment yield and runoffhave a very significantly positive correlation. The runoff coefficient of the bare and milletland is more than0.5, runoff coefficient of bare land on gneiss sloping reaches to0.98,under there kinds of land use patterns, soil loss rate is0.22～1, soil loss rate of grassland is only0.22.Nutrient loss representation: bare land> millet land> grassland. Each time slotthe concentration of kinds of nutrients in the sediment are not much diversities, due to thedifferent sediment yield, the total amount of nutrient loss varies widely, the largest amountof loss is potassium, followed by nitrogen and phosphorus loss is the minimum. Nutrientconcentrations have no evident positive correlation with the amount of nutrient loss, butthere are significantly positive correlation between total N、P、K and sediment yield; loss ofP and K is mainly bound to sediment yield. N loss in the rain is composed of sedimentnitrogen and dissolved nitrogen.3. There are differences between soil erosion and nutrient loss in different periods ofmillet and grassland. With the days of millet growth increasing, the vegetation coverageincreases, the runoff time also increases:60th day>40th day>20th day>0day. In differentperiods of millet the steady flow time is not same. The steady flow time of any stage ofmillet growth lags behind the0day of millet land. On gneiss hill sloping runoff andsediment dynamic processes are similar, it presents that flow rate is increasing untill thepeak runoff, then tends to be stable；sediment yield rate firstly increases and then decreasesto a certain extent sediment yield rate does not reduce. At different growth periods of millet,runoff, sediment yield and runoff coefficient are different. Millet production flow andcoverage have a negative correlation, runoff, sediment yield and runoff coefficient show:60th day <40th day <20th day <0day. At different growth periods of millet land, sedimentyield and runoff have a extremely significant positive correlation, with the days increasingoverland flow decreases, the sediment modulus decreased. There is a significantly positivecorrelation between amount of nutrient loss and sediment yield. The greater of runoff andsediment yield, the greater is the amount of nutrient loss. runoff and sediment yield in grassThere are not significantly different on different days of grass, when weed growth into the20th day, the vegetation coverage reaches70%, flow and sediment yield decrease sharply,runoff and sediment are no change between40th day and60th day of grass. The wholegrowth period, yield of grassland is0.096m3, the sediment modulus of723.96g/m2. Thegrass of the growth period of production flow is0.071m3, the sediment modulus of404.82g/m2. Bare land production flow is0.118m3, the sediment modulus of950.28g/m2.