| On northern semi-arid area of loess plateau of China, because of sparse precipitation and long time drought, deep soil desiccation and crop yield reduction caused by drought stress occurred widely on dryland of grain crop field, and it threats the sustainable development of dryland grain crop production severely. Based on widely field soil moisture and grain crop yield investigation, the crop-soil process simulation model WinEPIC (Evironment-Policy Integrated Climate) ,developed by USA, was used to simulate and analyze yield and soil water dynomic of continuous spring wheat, spring corn and potato under different fertilization level treatments. The soil desiccation effects and yield stability of grain crop field under various fertilization treatments were evaluated, and soil water carrying capacity and reasonable fertilization level, which is adapted to local rainfall condition and good for sustainable soil water use were determined. The results provided scientific foundation for sustainable and high yield grain crop groduction on dryland of northern semi-arid area of loess plateau. The progresses of this study are as following:(1) Field soil water investigation results showed that soil moisture decreased and thickness and distributed depth of desiccated soil layers on grain crop fields increased gradually as grain crop yield increased. Average soil moisture of 0-600cm soil layers on various grain crop fields was 11.46%, 14.37% and 9.27% respectively at Guyuan and Dingxi of semi-arid and Haiyuan of semi-arid prone drought areas of loess plateau. Except low-yield potato field at Guyuan, soil desiccation had already occurred on all kinds grain crop field.(2) Databases of daily weather variable sequence, physical and chemical properties of soil profile, crop growth parameters of WinEPIC model at Guyuan, Yulin and Haiyuan were established. Model verification results showed that, WinEPIC model could accurately simulate crop yields and deep soil moisture dynamics under different levels of fertilization treatments on the loess plateau. Four fertilization treatments on three locations used in the simulations were no fertilization treatment (N 0 kg/hm2,P2O5 0 kg/hm2),low fertilization treatment (N 60 kg/hm2,P2O5 30 kg/hm2), medium fertilization treatment (N 90 kg/hm2,P2O5 45 kg/hm2) and high fertilization treatment (N 120 kg/hm2,P2O5 60 kg/hm2). (3) During 1960-2000 simulation period, grain yield of the crop at Guyuan under no fertilization, low fertilization, medium fertilization and high fertilization treatment decreased significantly with fluctuation; the average yield of spring corn was 1.709 t/hm2, 2.353 t/hm2, 2.644 t/hm2 and 2.782t/hm2 respectively, and the average yield of spring wheat was 1.439 t/hm2, 2.067 t/hm2, 2.460 t/hm2 and 2.669 t/hm2 respectively. The spring corn yield was significant difference in stability than spring wheat under the different fertilization treatments. Thickness and distributed depth of desiccated soil layers on spring wheat and spring corn field increased gradually as year of continuous cropping and amount of fertilizer applied increased .Simulated monthly available soil water amount of all 4 fertilization treatments declined with annual and seasonal fluctuations in 0-7m soil layers, very strong soil desiccation on spring wheat and spring corn field had occurred at the beginning period of the crop growth simulations, and available soil water amounts fluctuated with rainfall change for a long period at low level after soil desiccated. Guyuan of semi-arid areas of loess plateau was suitable for planting spring wheat. Soil water carrying capacity of wheat field was 2.262-2.555 t/hm2, and its fertilization amounts were N 60-90 kg/hm2 and P 30-45kg/hm2.(4) During 1960-2000 simulation period, grain yield of the crop at Yulin under no fertilization, low fertilization, medium fertilization and high fertilization treatment decreased significantly with fluctuation; the average yield of spring corn was 1.148 t/hm2, 1.584 t/hm2, 1.737 t/hm2 and 1.843 t/hm2 respectively, and the average yield of spring wheat was 0.943 t/hm2, 1.486 t/hm2, 1.702 t/hm2 and 1.873t/hm2.The spring corn yield was significant difference in stability than spring wheat under the different fertilization treatments. Thickness and distributed depth of desiccated soil layers on spring wheat and spring corn field increased gradually as year of continuous cropping and amount of fertilizer applied increased. From the stability of crop yields, the intensity of soil desiccation and the sustainable use of soil water in grain crop fields into overall consideration, Yulin was suitable for planting spring wheat than sprin corn. Soil water carrying capacity of wheat field was 0.943-1.486t/hm2,and its fertilization amounts were N 0-60 kg/hm2 and P 0-30kg/hm2.(5) During 1960-2000 simulation period, average yield of spring wheat at Haiyuan was 1.144 t/hm2,1.589 t/hm2,1.852 t/hm2 and 2.008t/hm2 respectively under no fertilization, low fertilization, medium fertilization and high fertilization treatment; during 1960-1979 simulation period, average yield of Potato was 8.329t/hm2, 9.434t/hm2, 9.886t/hm2 and 10.198t/hm2 respectively under the four kinds of fertilization treatments.The spring corn yield was significant difference in stability than potato under the different fertilization treatment. Thickness and distributed depth of desiccated soil layers on spring wheat and potato field increased gradually as year of continuous cropping and amount of fertilizer applied increased. Simulated monthly available soil water amount of all 4 fertilization treatments declined with annual and seasonal fluctuations in 0-7m soil layers, very strong soil desiccation on spring wheat and potato field had occurred at the beginning period of the crop growth simulations. Soil water carrying capacity of wheat field was 0-1.1445t/hm2, and its fertilization amounts were N 0 kg/hm2 and P 0 kg/hm2,and the soil water carrying capacity of potato field was 8.329-9.434 t/hm2, and its fertilization amounts were N 0-60 t/hm2 and P 0-30 kg/hm2.(6) In the simulation period from 1960 to 2000, the average annual precipitation were 438.2mm,387.8mmand 380.6mm at Guyuan, Yulin and Haiyuanrespectively, and all of them decreased significantly with fluctuation. During 41-year simulation study, grain yield of the continuous spring wheat at Guyuan,Yulin and Haiyuan decreased significantly with fluctuation,its average were 2.067 t/hm2,1.486 t/hm2 and 1.589 t/hm2.Thickness and distributed depth of desiccated soil layers on spring wheat field increased gradually as its growing year increased,and simulated monthly available soil water amounts declined with annual and seasonal fluctuations in 0-7m soil layers, very strong soil desiccation on spring wheat field had occurred at the beginning period of the crop growth simulations, and available soil water amounts fluctuated with rainfall change for a long period at low level after soil desiccated. Distribution depth of desiccated soil layers of spring wheat field at Guyuan,Yulin and Haiyuan were within 2-3m soil layers after 8,7 and 6-year spring wheat growth respectively under high fertilization treatment, then soil moisture kept stable desiccated condition without change, only soil moisture in 0-2m soil layer changed with annual rainfall. Compared to Guyuan, spring wheat yield at Yulin and Haiyuan was lower, yield fluctuation was stronger and soil desiccation rate was faster. |
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