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

Loess Plateau has developed into one of the largest planting areas and the most outputareas of China, and apple industry has become one of the major industries of the local ruraleconomic development. Loess Plateau is located in a semi-humid and semi-arid climatic zone,there apple orchards are mainly rainfed and lack of artificial irrigation. But the growing ofapple trees need a lot of water, resulting in the orchards of deep soil desiccation and yieldsvolatility exacerbated. To improve the productivity, farmers applied too much nitrogenfertilizer into the apple orchards. It is not only exacerbated the soil water over consumption,but also lead to deep orchard soil nitrate accumulation. Apple production bases of LoessPlateau face a serious threat to long-term sustainable development. So we studied nitrogencontents of apple orchards. Contents of soil total nitrogen, ammonium nitrogen and nitratenitrogen of apple orchards were measured at6counties of apple production bases ofFengxiang, Baishui, Changwu, Xifeng, Yan’an and Jingning in the Loess Plateau. And profiledistributions of soil total nitrogen, ammonium nitrogen and nitrate nitrogen contents betweendifferent ages of apple orchards at different sites were analyzed and compared. Nitrogenfertilizer recommendations for these apple production areas were put forward.The WinEPIC model was used to simulate the apple yields and soil water content oftreatments with different planting densitiy or nitrogen fertilize applied apple orchards inFengxiang and Baishui apple-producing areas of south Loess Plateau in1965-2009, anddifferences of the treatments with different planting density or nitrogen fertilizer appliedorchard production, soil available water content and0-15m soil profile humidity wereanalyzed and comparatived. Then the appropriate local planting density and planting yearsand nitrogen fertilizer applied amount were determined. The main results of the study are asfollowings:1. The study of soil nitrogen of apple orchards on the Loess Plateau showed that:(1) The range of soil total nitrogen contents is from0.19g/kg (Yan’an) to1.28g/kg (Baishui), the range of soil ammonium nitrogen contents is from5.19mg/kg (Jingning) to39.46mg/kg (Changwu), and the range of soil nitrate nitrogen contents is from3.97mg/kg(Yan’an) to352.86mg/kg (Baishui) at different sites and of different ages of apple orchards.There are not significant differences of soil total nitrogen contents in apple orchards atdifferent sites except Yan’an where the content is obviously lower than those of other sites.(2) The soil total nitrogen contents in0~60cm soil layers of the apple orchards areobviously higher than those in the deeper soil layers. The soil nitrate nitrogen contents of oldapple orchards are higher than those of young apple orchards, and at the same time the nitratenitrogen accumulation in soil profiles below100cm soil layers occurs in varying degrees.(3) The contents of soil total nitrogen, ammonium nitrogen and nitrate nitrogen of appleorchards at Yan’an are obviously lower than those at other experiment sites, which meansmore nitrogen fertilizer should be used appropriately to increase apple yields. However,nitrate nitrogen contents in deep soil layers of apple orchards at Fengxiang, Baishui,Changwu, Jingning and Xifeng are relatively higher, hence nitrogen fertilizer utility should bekept at present level or reduced.(4) The soil nitrate nitrogen contents are significantly different, while the soilammonium nitrogen contents are less different between different ages of apple orchards atdifferent sites of the Loess Plateau. And the nitrate nitrogen accumulated in soil profiles.2. Simulation results of apple yields and soil water dymanics of treatments withdifferent plant density of apple orchards on south apple production region of Loess Plateaushowed that:(1) During the simulation period of1965-2009, the apple yields of different plantingdensity apple orchards of Fengxiang and Baishui were changing positively with precipitation.The apple yields increased with the planting density increased, and it slowed down whenplanting density reached833~1000plants per hectare. With the increasing planting density,soil available water capacity of apple orchards decreased, and the rate of the formation ofdeep dried soil layer increased.(2) By analyzing the evolution and amplitude of variations of the apple yields, droughtstress days, available soil moisture capacity and soil moisture distribution， the optimumplanting density was D3(2.5m×4m) or D4(3m×5m)，i.e.833~1000plants per hectare, andthe optimum cultivation years of apple orachards were30years at Fengxiang and25years atBaishui.3. Simulation results of apple yields of treatments with different nitrogen fertilizerapplied of apple orchards on south apple production region of Loess Plateau showed that:(1) During the simulation period of1965-2009, the apple yields of apple orchards with different nitrogen fertilizer applied treatments of Fengxiang and Baishui were changingpositively with precipitation. Annual production had small differences in the pre-simulationperiod under different fertilization treatments, but differences are obvious during the latersimulation period. The apple yields increased with the nitrogen fertilizer amount increased.(2) In42year apple production period of1968~2009, the yields of apple orchards underdifferent nitrogen fertilizer applied amount increased gradually at first, and then declined atFengxiang. And in the period of1968~2009, the yields of apple orchards under differentnitrogen fertilizer applied amount increased gradually of Baishui.(3)The optimum nitrogen fertilizer applied amount of Fengxiang is375kg/hm2or450kg/hm2, and that of Baishui is450kg/hm2.