Effect Of Applying Leaf Litter Of Trees To Control Soil Polarization Of Farmland

Soil degradation and continuous cropping obstacle are common problems in agricultural production, and the farm soil properties polarization(the soil properties deviate from original balance state and develop extremely toward one direction or develop non-balanced in the long process of continuous cropping)is one of the main reasons. In addition to fertilizing the organic manure, introducing other appropriate species to build an composite tree-crop intercropping system and applied the leaf litters to the soil are important ecological measures. Through the method that collect typical wheat field soil and leaf litters of different trees in the Residual and Gully Region of Loess Plateau, mixed and cultured them in the lab, the author studied the polarization trend of the continuous wheat soil properties and the effect of leaf litters on the soil. The results shows that:1 The continuous cropping of wheat can cause positive (benefical) polarization of the soil available zinc, available manganese, soil organic matter and varieties of enzyme activity, however, it can cause negative (destructive) polarization of the available iron(-43.66%,the rate of the increasement or the enhancement , the same as below), available copper(-15.76%), soil pH valu(e-0.26%), soil available nitrogen(-36.16%), available phosphorus(-20.46%), available potassium(-4.39%), cation exchange capacity(-11.13%), urease activity(-27.19%)and peroxide enzyme activity(-2.73%).2 The leaf litters decomposition can prevent the negative polarization of the available nitrogen in the continuous wheat field soils after the introduction of Malus pumila, Juglans regia, Prunus persica, Prunus armeniaca, Diospyros kaki, Morus alba, Zizyphus jujuba, Zanthoxylum bungeanum to intercrop with the wheat field soils; except for Prunus persica, the leaf litters decomposition of other tree species can prevent the negative polarization of the urease; except for Prunus armeniaca, the leaf litters decomposition of other tree species can prevent the negative polarization of available phosphorus and the cation exchange capacity; except for Morus alba, the leaf litters decomposition of other tree species can prevent the negative polarization of available iron.From the effect of leaf litters on the wheat field soil point of view, the most suitable tree species for tree-crop intercropping is Prunus armeniaca, Diospyros kaki, followed by Prunus persica, Zizyphus jujuba; and Malus pumila, Juglans regia, Morus alba, Zanthoxylum bungeanum are not suitable for tree-crop intercropping.3 The leaf litters decomposition can prevent the negative polarization of the urease, the cation exchange capacity, available copper, available iron in the continuous wheat field soils after applied the leaf litters of the afforestation tree species including Robinia pseudoacacia, Populus simonii, Quercus liaotungensis, Hippophae rhamnoides, Caragana intermedia. But at the same time, the leaf litters decomposition of Robinia pseudoacacia can promote the negative polarization of the Peroxide enzyme, available phosphorus, available potassium; the leaf litters decomposition of Populus simonii can promote the negative polarization of the soil available nitrogen, available phosphorus, available potassium; the leaf litters decomposition of Quercus liaotungensis can pomote the negative polarization of the Peroxide enzyme, available nitrogen, available potassium; the leaf litters decompositon of Hippophae rhamnoides can pomote the negative polarization of the available potassium.From the effect of leaf litters on the wheat field soil point of view, the leaf litters of Hippophae rhamnoides and Populus simonii are most suitable to apply to the continuous wheat field soils, followed by Robinia pseudoacacia, and the leaf litters of Caragana intermedia and Quercus liaotungensis are not suitable to apply to the continuous wheat field soils.4 The leaf litters decomposition can prevent the negative polarization of the cation exchange capacity in the continuous wheat field soils after applied the leaf litters of the urban tree species including Platanus orientalis, Sophora japonica, Ginkgo biloba, Salix babylonica), Acer mono Maxim Carr, Ligustrum lucidum, Prunus cerasifera Pissardii, Koelrenteria paniculata, Magnolia denudata, Firmiana platanifolia, Paulownia fargesii, Eucommia ulmoides, Aesculus turbinata. Except for Platanus orientalis, the leaf litters decomposition of the other tree species can prevent the negative polarization of the available copper; except for Magnolia denudata, the leaf litters decomposition of the other tree species can prevent the negative polarization of the available iron; except for Ligustrum lucidum and Firmiana platanifolia, the leaf litters decomposition of the other tree species can prevent the negative polarization of the soil available nitrogen; except for Acer mono Maxim Carr and Prunus cerasifera Pissardii, the leaf litters decomposition of the other tree species can prevent the negative polarization of the available potassium; except for Acer mono Maxim Carr, Prunus cerasifera Pissardii and Paulownia fargesii, the leaf litters decomposition of the other tree species can prevent the negative polarization of the the urease; except for Sophora japonica, Paulownia fargesii and Aesculus turbinata, the leaf litters decomposition of the other tree species can prevent the negative polarization of the Peroxide enzyme; except for Platanus orientalis, Ginkgo biloba, Ligustrum lucidum, Prunus cerasifera Pissardii, Firmiana platanifolia and Aesculus turbinata, the leaf litters decomposition of the other tree species can prevent the negative polarization of the available phosphorus.From the effect of leaf litters on the wheat field soil point of view, the leaf litters of Eucommia ulmoides and Prunus cerasifera Pissardii are most suitable to apply to the continuous wheat field soils, followed by Koelrenteria paniculata, Sophora japonica, Salix babylonica, Paulownia fargesii, the leaf litters of Ligustrum lucidum, Platanus orientalis, Ginkgo biloba, Firmiana platanifolia are most inapplicable to apply to the continuous wheat field soils, followed by Aesculus turbinata, Magnolia denudata, Acer mono Maxim Carr.