Process of Loss of Soil and Water in Red Soil and Purple Soil Areas of Recovering Plants

A long-time local investigation was conducted,according to the arranged proportion of 2∶1∶1∶1,on all the protecting forest,protecting timber forest,protecting economical forest,and protecting firewood forest.The results are obtained as follows:(1) In the first period of 1～4 year,erosion unit area decreased 38.98% and 36.05%;the averaging sediment decreased 41.19% and 18.43% in the red soil area and purple soil area.In the period of 4～7 year,erosion unit area decreased 99.86% and 75.73%;the averaging sediment decreased 97.52% and 78.00%.(2) In the 7th year,erosion in red soil area is 3.42 t·km~(-2)a~(-1),lower than permitted erosion;the erosion in purple soil area is lower than permitted erosion but according to the level of nutrient loss,it is not so if the level is speeding to produce soil.(3) The loss of soil and water in red soil area is lower than that in P/purple soil area,the decreasing speed of the soil and water loss in red soil area is bigger than that in purple soil area.(4) The soil and water loss takes place easily when the precipitation is more than 10.1 mm/day in two types of soil areas.Main loss of soil and water is produced by the precipitation of more than 25.1 mm/day.