Study on the general properties of runoff solid from sloping field in red-soil upland

he results show that 80% of the soil particles in the runoff solid is silt and clay in the sloping field of red soil.Compared with the particles in surface soil,the amount of sand in runoff solid decreases by 24.3%～30.8%,while the amount of silt increases by 11.4%～15.9% and the amount of clay is similar.The changes of particle components respond to various managing patterns during 1993～2001.In runoff solid,the amount of sand in 2001 is 30.0%～53.8% lower than that in 1993,while the amounts of silt and clay are 18.0%～21.2% and 3.8%～9.4% higher than those in 1993,respectively.The silt-increasing in runoff solid is significant in the multiple cropping system of rape-maize/sweet-potato,while silt-increasing and clay-increasing in runoff solid are significant in the vegetative cover structure of arbor-shrub-grass.The nutrient enrichment rates in both managing patterns show that water extractable N＞available K＞available P≥total N＞total K≥total P＞organic matter.Moreover,all the enrichment rates decrease significantly with the improvement of soil fertility.In runoff solid,most of the organic carbon enriches in the soil particle whose diameter is 0.05～0.001mm,N in the particle whose diameter is ＜0.01mm,K in the particle whose diameter is ＜0.005mm.Each nutrient enrichment amount accounts for over 73.5% of the relevant enrichment amount in runoff solid.P is distributed in various particles.