Nutrient Cycling Of Trees In Common Agroforestry Systems In Weibei Aera Of Shannxi Province

Because water and soil loss is serious and ecological environment is fragile in Weibei aera, so agroforestry systems play an important role in improving he original ecological environment and enhancing soil productivity. Through study on nutrient cycling of trees in common agroforestry systems in Weibei aera of Shannxi Province, agroforestry systems in coordination between species were selected, applied in reconstructing and rebuilding existing agroforestry systems; Trees and crop in coordination growth in agroforestry systems were ensured, economic and ecological benefits of agroforestry ecosystems were fully played, soil fertility and sustainable development of agroforestry systems were maintained, and provided scientific basis for species selection of agroforestry systems.Though experiment research, this paper gets the following results:(1) There were high biomass in bole and fruit of aboveground organs in fruit-crop intercropping types, the proportion is 37.94% and 24.14%.The second is branch with the proportion is 17.73%.Biomass' order showed :bole>fruit> branch > twigs>leaves>bark. Judging from different species,the bole of Ziziphus jujuba,Morus alba L and Prunus pseudocerasus Lindi had the highest biomass ,the reserves between 39.8 and 73.2 t/hm~2.The fruit of Ziziphus jujuba,Morus alba L and Pyrus bretschneideri Rehd had highest biomass,the reserves between 19.4 and 54.6 t/hm~2,There were high biomass in bole and branch of aboveground organs in forest-crop intercropping types, the proportion is 72.8% and 14.5%. Biomass' order showed:bole>branch > twigs>leaves>bark.Judging from different species,the bole of Acer truncatum Bunge and Toona sinensis Roem have highest biomass,the reserves between 110.6 and 95.9 t/hm~2.The bole of Eucommia ulmoides Oliv have the lowest biomass, the reserves is 23.4 t/hm~2.Annual productivity of organs aboveground in fruit-crop intercropping showed: fruits> leaves> branches>bole> bark.Annual productivity of organs aboveground in forest-crop intercropping showed: leaves>bole > branches>bark.(2) Plant nutrient elements distribution characteristics significantly different. The content of N,P,K in leaves was higher than other photosynthetic organs, the content of nutrient in bole was the lowest, the order of content of nutrient in different organs showed: leaves>twigs>fruit>bark> branches >bole. On the same nutrient element in the content of different species concerned, Ziziphus jujuba,Morus alba L,Juglans regia L,Diospyros kaki Thunb,Toona sinensis Roem and Prunus pseudocerasus Lindi had the highest storage of total N and available N in soil, the reserves between 12.23～16.08 g/kg .Ziziphus jujuba,Prunus pseudocerasus Lindi,Toona sinensis Roem,Prunus persica and Diospyros kaki Thunb had the highest storage of available P, the reserves between 1.72～2.19 g/kg. Morus alba L,Toona sinensis Roem,Ziziphus jujuba and Diospyros kaki Thunb had the highest storage of available K, the reserves between 7.03～10.45 g/kg . The rest of the tree species nutrient element N,P,K content was low.(3) Through analysis of annual absorption,annual retention and annual return in different agroforestry systems, that the reserved quantity of nutrient elements was between 17.49 kg/(hm~2ï¹'a)～327.94 kg/(hm~2ï¹'a). the reserved quantity of Prunus pseudocerasus Lindi,Morus alba L,Ziziphus jujuba,Acer truncatum Bunge and Toona sinensis Roem were highest, all of them were above 114 kg/(hm~2ï¹'a) . The nutrient elements of return was large than the reserved quantity. Generally range between 38.27 kg/(hm~2ï¹'a)～927.56 kg/(hm~2ï¹'a). The return quantity of Morus alba L,Ziziphus jujuba and Toona sinensis Roem were the highest. But the return quantity of Prunus armeniaca L was 38.27 kg/(hm~2ï¹'a) was the lowest. As to different nutrient element was concerned, the amount of N in return quantity was between 29.29～742.73 kg/(hm~2ï¹'a). The amount of P in return quantity was between 1.33～93.50 kg/(hm~2ï¹'a). The amount of K in return quantity was between 7.65～265.03 kg/(hm~2ï¹'a). Diospyros kaki Thunb and Prunus armeniaca L. had lowest annual absorption, annual retention and annual return were low, nutrient cycling and circulation were slow.(4) Utilization coefficient of three nutrient element in different trees was in order: N>K>P. Utilization coefficient of N in trees was between 7.69～16.08, difference of ability of trees using N was not significant, maintaining at a relavtively balanced state. Utilization coefficient of P in trees was between 0.92～2.19. Utilization coefficient of K in trees was between 3.76～10.46. Circulation coefficient of N in trees was between 23.34～94.68. Circulation coefficient of P in trees was between 3.03～93.62.Circulation coefficient of K in trees was between 8.32～89.35. Overall, fruit-crop intercropping types was higher than the fruit-crop intercropping types in Circulation coefficient of N,P,K.