| Soil erosion and resultant loss of surface soil fertility are major threats in reducing the potential of crop production in Purple soil of south western Sichuan province of China.Nutrients mass losses are controlled by their pools in the soil surface layer which is exposed to water erosion and the effects of rainfall intensity and slope on this pool are seldom studied.Therefore,various rainfall simulated experiments were conducted to evaluate the effect of rainfall intensities(33 mm h-1,54 mm h-1,94 mm h-1 and 120 mm h-1)and(5° 15°and 25°)slopes on sediment and water losses,infiltration rate and water recharge coefficient(RC)in un-mulched and mulched soil trays.After rainfall simulations,soil surface layer of 10 mm thickness from each tray was removed and variations in soil particle sizes distributions and soil organic carbon(SOC),total nitrogen(TN),available nitrogen(AN),total phosphorus(TP),available phosphorus(AP)and total potassium(TK)contents in response to different rainfall intestines and slopes were investigated.Sediment and water losses increased with rainfall intensity and slope steepness under mulched and un-mulched conditions.The maximum sediment and surface runoff losses of 876.2 gm-2 and 681 mm·m-2 were recorded in un-mulched soil during rainfall intensities of 94 mm·h-1 and 120 mm·h-1 at the 25° slope.Generally,the slope contribution(Sc)on water and sediment losses decreased with increasing rainfall intensity and slope steepness.In un-mulched conditions,water losses were independent of slope steepness during the highest rainfall intensity.However,in mulched soil,higher contributions of slope(Sc)and rainfall(Rc)were found for water runoff and sediment losses(>50%),except during the increase in slope steepness from 15° to 25° under the highest rainfall intensity(120 mm·h-1).The effectiveness of mulch was more pronounced in reducing sediment losses(81%-100%)compared with water losses(14%-100%).The conservation effectiveness of mulch decreased and increased with slope steepness for water and sediment losses under higher rainfall intensities.Water infiltration and recharge coefficient(RC)decreased with increased slope steepness.Moreover,with increase in rainfall intensity,the water infiltration increased while the RC decreased in both mulched and un-mulched soil.In un-mulched soil,clay contents(0-2?m)decreased significantly(p<0.05)with slope steepness during lower rainfall intensities(33mm h-1,54mm·h-1).However,during higher rainfall intensities clay(0-2?m),fine silt(2-20?m)and coarse silt(20-50?m)tended to increase while the sand contents decreased significantly(p<0.05)at higher(15° and 25°)slopes compared with 5° slope.In the mulched soil,clay(0-2?m)and coarse silt(20-50?m)contents decreased significantly at 5° slopes compared with steeper slopes only under rainfall simulations of 94 mm h-1 and 120 mm h-1,respectively.Rainfall intensity had negatively correlated with clay and fine silt contents while mulch had significantly correlation with fine silt.Average SOC,total N and available N contents significantly decreased with increase in slope and rainfall intensity in unmulched soil whilst they were only decreased with increase in rainfall intensity in mulched soil.However,there were non-significant differences in the TK contents under the different rainfall intensities and slopes both in mulched and un-mulched conditions.The average contents of total and available P decrease significantly in the surface soil at the 5°slope compared with higher slopes under all conditions.Moreover,like SOC and N,P(total and available)contents significantly reduced with increasing rainfall intensity.After rainfall simulations,clay and silt size particles were substantially reduced while sand contents increased in top surface layer of 10 mm thickness compared with pre-simulated soil both in mulched and un-mulched conditions.Soil fine particles and nutrients pool in soil surface layer decreased in all conditions compared with their respective contents in pre-simulated soil.However,mulch maintained significant higher fine silt contents and SOC,TN,TP and TK contents compared with unmulched soilResults suggests that;1)mulching the soil surface is one of the best management practices for reducing soil erosion and maintaining soil fertility,2)mulching effectively promoted water infiltration and water recharge coefficient,3)mulched soil maintained a significantly higher nutrient pools compared to that of the un-mulched and,4)both lower slopes,and rainfall intensities,and mulch facilitate the transport of soil fine material and nutrients into lower soil layers and nutrients losses could be reduced in succeeding rainfall events. |
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