Soil Conservation For Several Patterns Of Converting Lands Into Forests In HONGYA, SICHUAN

To understand conservation of soil under different patterns of converting lands into forests and farmland,four patterns and farmland were chosen as the sampling spots in Hongya, Sichuan during two-year time.The results indicated that:First,effects of converting lands into forests on soil were mainly as following:(1) Soil nutrient:In the early days of converting lands into forests.soil total nitrogen(except for pattern â…  in top soil), NO3--N (except for pattern â…¢ in lower soil), rapidly available potassium (except for pattern â…£ in lower soil and pattern â…¡ ) and total potassium(except for pattern â…£)increased,while pH, available phosphate, total phosphate (except for pattern â…  and pattern â…¢), slowly available potassium, hydrolysable and NH4+-N had decreased.Content of organic matter was relatively stable and would have no obvious changes in a short time. In early days of converting lands into forests,the changes of soil nutrient under the patterns was unstable.(2) Soil bulk density and porosity: Soil bulk density increased from top level to lower level under the patterns.It showed that the top level soil was loose, which was relative with accumulation of litter and its decomposition speeds.Compared with that of farmland, total porosity and capillary porosity in the top soil for the several patterns of converting lands into forests were much higher.(3) Soil mechanical composition: In the top soil(0~20cm), the amounts of sand of different patterns of converting lands into forests was lower than that of farmland, while the amounts of clay and physical clay was higher than that of farmland.Second,Soil nitrogen, phosphate and potassium' s temporal changed had obvious dynamic characters:(1) The mean value of soil NH4+-N was rising since April and the highest level appeared in summer(June and July) and the lowest level appeared in winter except for pattern â… ; The mean values of soil NO3--N of pattern â…£ was the highest in April,while the others and farmland were the highest in June. The mean values of soil NO3--N of all patterns showed the lowest level in August.(2) The value of soil available phosphate was rising since April and the lowest levelappeared in August.(3) Dissolved potassium of four patterns in the soil at two depth decreased from April and appeared the lowest level in July except for farmland. Dissolved K began to recover since July and showed lower level in September.Third,dynamic characters of soil nutrient content were dependent on the comprehensive effects of environment and vegetation. Rainfall, agricultural actions and plant growth rhythm would in some degree influence soil nutrient content.Fourth,as far as the improved effects on forest soil after converting lands into forests were concerned, pattern â…¢ was the best one among all patterns about the top level soil;while pattern â…¡ was the best one about the lower soil.Because the observation time was short, the results only reflected the effects in the early of the engineering of converting lands to forests. The situation of soil nutrient in the future needed to be further studied.Fifth,based on dynamic characters of soil nutrient content of these patterns and farmland, to prevent soil nutrient from deceasing, enhance nutrient-use efficiency and improve productivity of forest land, the suggestion was proposed that do not cut forage grass between May and August, applying organic fertilizer and paying much attention to the tending and manangement of trees or bamboos.