Research On Litterfall Decomposition And Soil Nutrient In Agroforestry Systems In Purple Soil Area

In the hilly area of the central Sichuan basin, the agricultural ecosystem had become flimsy comparatively at a disadvantage because of the high reclamation index, the illness of land using and the seriousness of soil and water erosion. The reducing of crop yield would be resulted from conceding the land to forestry (or meadow). Agroforestry intercropping has been introduced in order that land resource and climate resource are utilized fully, the erosion of soil and water is controlled, and the income of farmers is increased, the energy of country economy is improved. Agroforestry intercropping has also combined complete or part interdependent whole organically between forestry and crop or animal husbandry for the goal of continuous development. This article has pertinence to the non-irrigated farmland ecosystem about frangibility and retrogression in hilly regions of central Sichuan, and combines agroforestry intercropping in the measure of the local fruits (the loquat , apricot , pear) —grain, and has studied on the rotten litterfall of fruit tree and impact on content of soil nutrients of intercropping for leaves, and has discussed the change characteristics of the Carbon, Nitrogen, Phosphorus, Potassium in the soil of fallen leaf of fruit tree, and the influence rule of soil Carbon, Nitrogen, Phosphorus, Potassium, Particle Organic Matter(POM) and the humus. The results show:In the system of agroforestry intercropping, return quantity of Apricot, Pear and Loquat trees' litterfall are 136.5kg/hm², 17.2 kg/hm² and 757.2 kg/hm² respectively. Using of coefficient model Ct =C₀- k×lnt can fit the change of organic carbon of litterfall well. With resolving in the soil, litterfall may increase in the rate of organic C decomposition, but the content of organic carbon of litterfall is reducing constantly. The litterfall of loquat tree resolve 95% for 15.8 years; The resolving coefficient of apricot fallen leaves is 9.45, takes 5.9 years to resolve 95%, and the resolving rate of pear leaf is 12.80, it takes 2.6 years to resolve 95%.The decomposition of fruit tree litterfall is a kind of slow and complicated course. Because circulation periods of Nitrogen and Phosphorus are long, the withered litterfall in soil can adsorb a certain amount Nitrogen and the Phosphorus of soil for a very long time, and produce the accumulation of the Nitrogen and Phosphorus. The size of accumulation rate of the nitrogen and phosphorus is: Leaves of the loquat > Leaves of the apricot > Leaves of thepear; But the content of Potassium in litterfall decrease, releasing amount as 0.88% - 1.02%, Leaves of the loquat > Leaves of the apricot > Leaves of the pear.The content of soil organic carbon presents the trend from reducing to increasing. Agriculture and forestry intercropping soil have own loss, and the content of soil organic carbon decrease; While the litterfall of fruit tree decompose constantly in soil, soil can absorb remnants organic and inorganic compound of the rotten leaves, and the absorption amount of soil organic carbon exceed oneself loss after the some time, the content of soil organic carbon increase, the range is 2.57g/kg- 0.22g/kg.In the system of agroforestry intercropping, the rotten leaves of fruit trees are cause to a transfer of soil organic carbon moving to smaller particulate. The POMR-C increase dissimilarly in the different proving ground, leaves of the pear > Leaves of the apricot > Leaves of the loquat; Nitrogen concentrate on 0.25mm 0.05mm particulate even smaller particulate of soil. When fallen leaves of fruit tree are decomposed, the soil loosely combined humus, stable combined humus and tightly combined humus change but not reach the remarkable level; Soil humic acid have a course from increase to reduce, and it is a turning point in 120 day when fallen leaves decomposed.Soil nutrient do not decrease for agroforestry intercropping, and there are the marked relativity between treatment and check, but in the Apricot intercropping soil organic matter may decrease for a change of soil nutrient. However, soil organic matter and Nitrogen may increase in the Pear intercropping. Agroforestry intercropping can reduce on Bulk density and increase soil porosity and improve soil aggregate structure. The effect of Pear intercropping is the best obvious because soil porosity is increased 1.51%, disperse coefficient is increased 29.29%; The effect of Loquat intercropping is the lowest.Crop yields (wheat, maize, sweet potato) are lower than check for agroforestry intercropping. The output of wheat, maize and sweet potato are decreased respectively with 7.33%, 26.27% and 22.19% in the Apricot intercropping. However, the output of maize is increased 0.20% in the Pear intercropping and the output of wheat is increased 0.20% in the Loquat intercropping. The analysis of economic benefit may indicate that the economic benefit of Pear and Loquat intercropping will be increased 5218.00 RMB/hm2 and 8690.00 RMB/hm2 compared with checks in the first year of fructification.It is an obvious effect of nutrient return for fallen leaves decomposed completely in the agroforestry intercropping in the hilly area of the central Sichuan, but a certain amount Nitrogen and the Phosphorus have been adsorbed by the withered litterfall in soil and the dense planting of fruit tree and the misuse of fertilizer will cause the decline of the ecological fertility of soil. We suggest that nitrogen and phosphorus fertilizer should be employed in agroforestry intercropping farmland in order to reinforcing the periodic shortage of nutrition element for litterfall decomposed. This has good function on improvement of the agroforestry intercropping productivity.