Study On Profile Patterns Of Soil Water And Nitrogen And Spatial Variability Of Soil Nutrients In Apple Orchard Of Luochuan County

The Loess Plateau is the most important apple-producing region in China.However,excessive fertilization in apple orchard has been extensively intensified in this area during the past 10 years,which could resulting in wasting fertilizer resources and deteriorating environment such as groundwater pollution.This study is conducted in Luochuan county,a typical area for apple planting in the Loess Plateau,and aimed to characterize the changes in vertical patterns of soil moisture and nitrogen after conversting cropland to apple orchard,and to determine the spatial distributions of soil nutrients in apple orchards at a county scale.The outcome would help us elucidate the long-term effects of apple-planting on soil quality and ecological environment,thus providing data support for developing sustainable apple production in the Loess Plateau.The main results are listed as follows:（1）Convering cropland to apple orchard significantly（P<0.05）affected the vertical distributions of soil moisture and nitrate,but not significant for soil NH₄⁺across the 0–600cm soil profile.8-yr-old apple orchards were similar in soil nitrate concentrations（SNC）,residual soil nitrate（RSN）,soil moisture content（SWC）and soil water storage（SWS）when compared with cropland.In contrast,the 17 and 25-yr-old apple orchards strongly decreased SWS by 150 and 230 mm,respectively,which was mainly associated with the SWC changes in soils deeper than 3-m.SNCs in the 0–500 cm layers increased significantly with the stand ages of apple orchard,and the 17 and 25-yr-old apple orchards received substantial RSNs,with the values of 6830 and 8370 kg ha^–1,respectively,which were appreciably higher than that of 8-yr-old apple orchard(440 kg ha^–1)and cropland(700 kg ha^–1).（2）The averaged amounts of fertilizers were 1340 kg N ha^–1,855 kg P₂O₅ha^–1 and 1180kg K₂O ha^–1,respectively,in the apple orchards of the Loess Plateau,indicating a severe excessive fertilization.（3）The averaged concentrations of soil organic matter,total nitrogen,available nitrogen,available phosphorus,available potassium and available zinc were 13.24 g kg^–1,0.77 g kg^–1,56.8 mg kg^–1,31.0 mg kg^–1,292 mg kg^–1 and 1.10 mg kg^–1,respectively,in the 0–20 cm layer of apple orchards in Luochuan County.The corresponding values were increased by43.9%,26.2%,38.5%,508%,195%and 179%,respectively,when compared with the data observed in the second national soil survey,and were also obviously higher than those of0–20 cm soil layer.Interestingly,the 0–20 cm soil layer was characterized with relatively high available phosphorus and potassium contents,with the value of 13.9 mg kg^–1and 195mg kg^–1,respectively.On the contrary,the p H values of 0–20 cm and 20–40 cm soil layers were 8.12 and 8.09,respectively,which were decreased by 0.18 and 0.21 units compared with the data of second national soil survey.（4）Correlation analysis showed that apple yield was significantly correlated with stand age of apple orchard,which could be well-fitted by a parabolical model.The highest yield was achieved at the stand age of～18 years.Soil quality indices obtained in the 0–20 cm soil layer were more sensitiveto reflect apple yield changes,when compared with those in the 20-40 cm soil layer.Notably,soil quality indices of apple orchards with 14～17 years were significantly correlated with apple yield in both 0-20 cm and 20-40 cm soil layers.The relationships between soil quality and stand age of apple orchards were not statistically significant across the studied 8-31 years apple orchards.Overall,we concluded that the enlargement of apple planting could result in soil water deficit（>300 cm）and nitrate accumulation in deep soil layers,and thus negatively affecting regional ecology of the rain-fed Loess Plateau.Thus,supplementary irrigation and strict controls on N fertilizer should be practiced.Additionally,avaliable P and K in soils of apple orchard exhibited a substantial surplus,implying the application rates of P and K fertilizers should be reduced in apple orchards.Meanwhile,managers in apple-producing area ought to pay more attention to organic fertilizer and integrated K fertilization management.