Characteristics Of Nitrate Accumulation And Leaching And Simulation Of Loss Control In Apple Orchards On The Loess Plateau

The Loess Plateau has become one of the high-quality apple producing areas in China,due to its unique geographical and climatic conditions.However,the long-term overuse of nitrogen fertilizer in apple orchards not only reduces utilization of nitrogen fertilizers,but also reduces apple quality and economic efficiency.What's more,it causes the nitrate accumulation in the soil profile and poses a threat to regional groundwater safety.This study focused on the national major needs of efficient utilization of fertilizer in agricultural system and regional environmental pollution control in the region.Targeting to the arbor and the transformated dwarf apple orchards from arbor orchard on the Loess Plateau,the objective of this study was to investigate the characteristics of soil nitrogen accumulation,its main factors and its controlling measurements.It was expected to provide a theoretical basis for optimizing fertilization management for apple orchards on the Loess Plateau and provide support for green production of the apple industry.The results are as follows:?1?87.2%of nitrogen in arbor apple orchards on the Loess Plateau was accumulated in the 0-2 m soil profile as the form of nitrate,and another 10%distributed in the soil layer below 2 m.Soil nitrate accumulation in deep soil layer has become the main way of nitrogen loss in apple orchards on the Loess Plateau.With the tree ages increased,the concentration and accumulation of soil nitrate in the soil layer increased,and the peak concentration position moved down award.The nitrate concentration at soil depth of 100-120 cm in 15-year orchard showed 4-17 times compared to 5-year orchards.The soil nitrate accumulation?0-6 m?of 5-year orchard in Luochuan increased from 769 kg ha^-1 to 6286 kg ha^-1 in 25-year orchard.The nitrate accumulation?0-6 m?of 25-year orchards on tableland and solpeland in Changwu was13885 and 2748 kg ha^-1,respectively.The amount of fertilization is the most important factor affecting the accumulation of nitrate in the soil.At the same time,soil nitrate accumulation is also closely related to soil water content and soil properties,while soil water is controlled by rainfall,terrain and other factors.?2?The nitrate accumulation in the 0-2 m soil layer of the dwarf apple orchards was as high as 2000 kg ha^-1.After two seasons,the accumulation of nitrate in the 0-2 m soil layer of this dwarf apple orchard in the N800,N400,NY50 and CK treatments was:5700,3188,893and 841 kg ha^-1;The soil nitrate increases?2-3 m?were 310,175,258 and 124 kg ha^-1,respectively.N800 had the largest leaching loss at a depth of 30 cm,which was 4.3 times that of other treatments.The total mineralization during the cultivation period of N800 and NY50treatments were 88 and 38 mg,respectively.And they were significantly higher than the treatment without fertilization.Without applying nitrogen fertilizer,apple yield did not decrease significantly,but the increase of nitrate in the 2-3 m soil layer reached 124 kg ha^-1after two year,and there was still 841 kg ha^-1 in the 0-2 m soil layer.The residual nitrate showed that the nitrate accumulated in the 0-2 m soil profile cannot be ignored in the new dwarf orchards transformed from old arbor orchards.Even it may continue to be leached for a long time without fertilization,so that we need to take measures now.?3?The results of the accumulation status of nitrate in arbor and dwarf apple orchards in the Loess Plateau showed that it will threat the regional groundwater security in the future,posing a threat to regional groundwater safety.A scenario simulation of soil nitrate accumulation regulation was carried out for controlling this situation in the soil before transformation from old orchards and the newly constructed dwarf orchards.According to the accumulation situation of old orchards before transformation,two years of alfalfa cultivation can effectively reduce the accumulation of nitrate in 0-2 m soil layer,reducing the impact of old orchard.To the newly constructed dwarf orchards,a method of using target yield to determine the applied fertilizer.Such as the recommended N application rate for the dwarf apple orchard is 150-180 kg ha^-1with the target yield of 80 t ha^-1.