Research On The Soil Nitrogen Dynamics And Nitrogen Use Efficiency In The Apple Orchard Of Water Storage Pit Fertigation

In recent years, due to the unreasonable fertilization and irrigation, resulted in serious pollution of groundwater and waster the shortage of water resources, nitrogen fertilizer utilization rate is low, the phenomenon of resources wasting was common to see. Therefore, a field experiment was conducted in apple orchard under water storage pit fertigation to study the distribution character of soil moisture contents; the distribution and seasonal change of soil ammonium nitrogen, nitrate nitrogen, alkali-hydrolyzale nitrogen subjected to different irrigation(450m3/hm2、600m3/hm、750m3/hm2)and N application rates(Okg/hm2、600kg/hm2、900kg/hm); apple tree nitrogen use efficiency, soil NO3--N accumulation contents and precipitation effect on nitrate nitrogen leaching. The aims were to find the optimized combination of irrigation and fertilization rates for water storage pit irrigation in apple orchard, at the same time, comparison water storage pit irrigation with surface irrigation finding water storage pit irrigation has many advantages. The main results were as follows:(1) Soil moisture content is less affected by time and space change under water storage pit irrigation, and accordance with soil bulk density in the vertical direction, water storage pit could storage soil moisture in the deep layer very good(2) N application and irrigation rates on the distribution section of soil ammonium nitrogen mainly near the water storage pit location, soil ammonium nitrogen contents there are no significant correlation with irrigation water and N application. the size order of seasons change is shown as:fruit maturity stage>full-bloom stage>after the fruit harvest>fruit rapid swelling stage>new shoot growing stage. But the value of ammonium nitrogen is stable, not more than3mg/kg.(3) The impact of N levels on the distribution of soil NO3--N are mainly concentrated in the0-120cm soil layer at vertical direction, the maximum increment in different depth between0-80cm, soil nitrate nitrogen increment arranged in water storage pit edge to the central peak with the increase of N application rate at the radial direction.Above the soil depth of100cm irrigation water for nitrate nitrogen increment effect was significantly greater than the soil depth below100cm, with the increasing of the horizontal distance and irrigation amounts at the radial direction, the content of nitrate nitrogen transfer to stay away from the water storage pit direction increased. Nitrate nitrogen seasonal variation is notable above the160cm soil layer, heavy rainfall is a great influence factor on the seasonal change of nitrate nitrogen.(4) Most of the soil alkali-hydrolysable nitrogen increased with the increasing of irrigation amounts at the vertical distance, the removing downward soil alkali-hydrolysable nitrogen contents become more when irrigation amount and radial distance increased, effective nitrogen show unimodal distribution in the horizontal direction, soil alkaline hydrolysis nitrogen difference between the two treatments in the horizontal direction with increasing vertical distance climb up and then decline. Available nitrogen with nitrate nitrogen and mineral nitrogen have the same spatial distribution regularities, the correlation coefficient is0.938and0.923, correlation is very high. The percentages of nitrate nitrogen take up alkali-hydrolysable nitrogen closely to70%, irrigation rate has a certain influence on the amount of nitrate nitrogen in the soil alkali-hydrolysable nitrogen, but has little effect on total content.(5) The increasing of nitrogen application significantly increased the accumulation contents of nitrate in the soil after harvest, the cumulative amount between1221.97-3899.9kg/hm2, accumulated nitrate nitrogen in120-200cm soil layer significant change as season, through integrated into account, N application influence of nitrate nitrogen accumulation is obvious more than irrigation.nitrogen use efficiency changes with the season in turns is remarkable under water storage pit irrigation, after the fruit harvest nitrogen use efficiency as high as21.381%. Comprehensive considered nitrogen use efficiency and soil nitrate nitrogen accumulation amounts thinking the W2N1processing is the optimal combination of water and nitrogen.(6) Compared with surface irrigation discovered water storage pit irrigation has the following advantages:Water storage pit irrigation has the efficacy of make full use of precipitations and sustained soil water. ammonium nitrogen has small seasonal changes, there are more ammonium nitrogen content in topsoil100cm and more other form nitrogen amount in effective nitrogen than surface irrigation, alkaline hydrolysis nitrogen distribution uniform; Nitrate nitrogen increment distribution area is wide,content uniform and significant seasonal changes than traditional irrigation; Nitrogen fertilizer utilization rate is higher than surface irrigation(16.506%); The amounts of nitrate nitrogen accumulation and leaching quantity under the impact of precipitation is less, effectively improve the environment of apple tree root zone nitrogen, promoting the growth of apple trees.