Simulation Of Water Productivity Of Rainfed Apple Orchard On North Apple Production Region Of Loess Plateau

Unique apple quality of hilly apple orchards at Yan’an city and Jingning country of appleproduction regions on the loess plateau is famous in apple market and widely appleproduction increased fast in the regions in recent years. Because of high planting density andfertilizer application seriously threatened the apple yield increase and quality improvement onrainfed apple orchards. With deep root systems and strong water consumption of apple tree,soil desiccation widely occurred on rainfed hilly apple orchards and degradation of appleorchards was serious. Because of apple tree has along growth period, we used the EPIC modelto simulate the potential productivity and changes of deep soil water of rainfed apple orchardsat Yan’an and Jingning from1965～2009, in order to choose the best management for appleorchards. Firstly, we measured soil water on different growth age apple orchards. Secondly,the WinEPIC model was used to simulate yield and soil desiccation effects of under differentplanting density, fertilization treatments at Yan’an and Jingning. The results of the study wereas following:1. Feild investigation results of apple orchards at Yan’an and Jingning showed asfollowing:(1) The soil moisture decreased in0～1000cm soil layers with the growth years of appletrees. As the soil moisture decreased, the thickness of drying layers increased and becamedeeper gradually with the growth years of apple tress.(2) The mean of soil organic matter at Yan’an and Jingning was3.1and6.1g/kg.Average soil total nitrogen contents was0.38and0.53g/kg. The soil organic matter and soiltotal nitrogen contents were lower at Yan’an than Jingning. All kinds of total and availablesoil NPK nutrient contents (except total potassium and available nitrogen) of apple orchardshad obvious "surface accumulation effect". In all kinds of soil nutrition indexes, variation oftotal NPK nutrient contents of apple orchard were lower than available NPK nutrient contents.2. EPIC model simulation results of apple orchards at Yan’an and Jingning showed asfollowing:(1) During the simulation period, annual yield increased rapidly in early growth stage,and then declined obviously with fluctuation when reached its maximum. The higher plantingdensity of the apple orchards had, the higher annual yield could obtain in early growth stage.Simulated annually available soil water amounts in0~15m soil profile under differentplanting density treatments decreased rapidly with strong fluctuation during early growth stage. Annually available water amounts fluctuated with annual and seasonal rainfall changesin range of0~600mm after17~22years growth at Yan’an and after13~20years growth atJingning. Annual soil moisture distribution characters in0~15m soil profile under differentplanting density orchards at Yan’an and Jingning were similar, i.e. deep soil desiccationoccurred after soil moisture declined sharply and thickness of desiccated soil layer increasedannually in early and middle growth stage. The depth of drying layer distribution could reach12m. Considering apple yield and available soil water amounts, Reasonable planting densityof apple orchard was650~800plants/hm~2at Yan’an and550~700plants/hm~2at Jingningrespectively.(2) During the simulation period, annual yield increased rapidly in early growth stage,and then declined obviously with fluctuation when reached its maximum. Different fertilizertreatments was significant at the earlier stage. Situations of soil nitrogen stress apple orchardsat Yan’an and Jingning were similar, and nitrogen stress decreased Water stress slowlyincreased along with nitrogen application increased. Annually available water amountsfluctuated with annual and seasonal rainfall changes in range of0~600mm after a long timeat Yan’an and Jingning. Reasonable fertilizer treatments of apple orchard was N4~N5（N360~450kg/hm~2）at Yan’an and Jingning.