| Based on widely yield investigation and deep soil moisture observation of grain crop fields on dryland, the WinEPIC (Environmental Policy Integrated Climate ) model developed by USA was used to simulate grain crop yields and soil desiccation effects under different cropping systems, fertilization treatments in different rainfall locations of middle areas of loess plateau during 1960-2000. The crop yield stability of and soil desiccation effects under different cropping systems and fertilization treatments were evaluated. The results provided basic scientific foundation for sustainable development of grain production on loess plateau. Progresses achieved were as followings:(1) The investigation results of crop yield and soil moisture indicated that, grain yield trend of continuous winter wheat and spring maize decreased while influenced by precipitation. Winter wheat yield was more sensitive to rainfall and spring maize yield more influenced by previous crop stubbles in rotation system. The soil moisture of high-yield field was lower than low-yield field. Soil desiccation phenomenon was remarkable from 1 to 3 m soil layers, and soil moisture decrease also could be observed in more deep soil layers.(2)The model validation results of winter wheat continuous cropping on dryland of Changwu highland, spring maize continuous cropping of Jinzhong semi-arid area, and winter wheat-spring maize rotation on dryland of Changwu highland showed as followings: the simulation results of crop yield and dynamic change of soil water for winter wheat continuous cropping, spring maize continuous cropping and winter wheat-spring maize rotation were relatively precise. The WinEPIC model could be used to simulate winter wheat continuous, cropping, spring maize continuous cropping and winter wheat-spring maize rotations on loess plateau.(3) Grain yield of spring maize continuous cropping at Luochuan, Changwu, Yan'an and Shouyang decreased by order during 41 years simulation , and its average yield was 4.40t/hm2, 4.23t/hm2, 3.75t/hm2 and 2.50t/hm2, respectively. The increased yield rate by fertilizer(IRF)of spring maize continuous cropping decreased with order of Changwu, Luochuan, Yan'an and Shouyang. Water use efficiency (WUE) of wheat fields was also with that order among four locations. The higher fertilizer applied of the treatment, the higher WUE would have. Monthly available Soil Water (MSW) in 0~7 m soil layers of Luochuan, Changwu, Yan'an and Shouyang decreased with order of location sequence, and it was more steady in the first two locations than the last two locations. Average MSW appeared as a decrease trend and fluctuated with increase of fertilizer amount. Comparing to the N0 treatment, available soil water amount of N60, N120, N180, N240 and N300 fertilization treatments decreased 166mm, 299mm, 295mm, 416mm and 421mm, respectively. After suffering soil water depletion and desiccated soil layer thickened, distribution of desiccated soil layer in four areas had shaped a steady desiccated layer. Soil desiccating rate increased with the order of Luochuan, Changwu, Yan'an and Shouyang. Fertilizer amount was an important impact factors on depth of desiccated soil layers. The higher fertilizer applied, the faster soil desiccating rate reached. Considering spring maize yield, WUE and IFR,soil moisture distribution in 0-7m profiles,the suitable yield and reasonable fertilizer amount of spring maize continuous cropping was 5.25-5.54 t/hm2 and N240-N300 at Luochuan, 5.25-5.45t/hm2 and N240-N300 at Changwu, 4.26-4.58 t/hm2 and N180-N240 at Yan'an, 2.34-2.74t/hm2 and N120-N180 at Shouyang, separately。(4) Grain yield of winter wheat continuous cropping at Luochuan, Changwu, Yan'an and Shouyang decreased by order during 41 years simulation , and its average yield was 2.77 t/hm2, 2.70 t/hm2, 1.97 t/hm2 and 1.00 t/hm2 respectively. The difference of IRF and WUE of spring maize continuous cropping were significant among four locations, which was from high to low by order of Changwu, Luochuan, Yan'an and Shouyang. MSW in 0~7 m soil layers of Luochuan, Changwu, Yan'an and Shouyang decreased by the order of location sequences, and it was steadier in first two locations than the last two locations. Comparing to the N0 treatment, available soil water amount of N120, N150, N180, N210 and N240 treatments decreased 111mm,110mm, 219mm, 220mm and 220 mm, respectively. Soil desiccating rate of N0, N120, N150, N180, N210 and N240 treatments increased with fertilizer amount increase, and it also increased with order of Luochuan, Changwu, Yan'an and Shouyang. Considering winter wheat yield, WUE and IFR,soil moisture distribution in 0-7m profiles,the suitable yield of winter wheat continuous cropping at Luochuan, Changwu, Yan'an and Shouyang was 3.59-3.78 t/hm2, 3.24-3.38 t/hm2, 2.08-2.43 t/hm2 and 0.69-0.89 t/hm2, respectively, and reasonable fertilizer amount in corresponding location was N210-N240, N180-N210, N150-N180 and N90-N120 respectively.(5) During 1960~2000 simulation period, R7 was the highest average yield rotation among 8 kinds of wheat-maize rotations (R1-R8) at Luochuan, Changwu, Yan'an and Shouyang, Considering from average yield, and R7 at Luochuan, Yan'an and Shouyang, R1 at Changwu was the highest economic returns rotation among 8 wheat-maize rotations. MSW in 0-7m soil layers of all rotations at four locations decreased during the simulation period. The lowest water stress days of rotation among 8 rotations was R7 at Luochuan, R2 at Changwu, R5 at Yan'an, and R7 at Shouyang, respectively. The winter wheat was more vulnerable to the draught threat than spring maize in winter wheat and spring maize rotation system. Taking full account of crop yield, economic effect, MSW in 0-7 m soil layers and soil desiccation speed, the optimal rotation at Luochuan, Changwu, Yan'an, Shouyang was R7 (Spring maize-Spring maize-Spring maize-Winter wheat), R1 (Spring maize-Winter wheat), R8(Spring maize-Spring maize-Spring maize-Winter wheat-Winter wheat), R7(Spring maize-Spring maize-Spring maize-Winter wheat). |
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