| Oasis is a core place for the development of society in arid regions.Because of the limited water,there is a trade-off between agricultural scale and ecological scale.How to realize the efficient use of agricultural water and soil resources by determining the suitable agricultural scale and the optimal agricultural development structure in the socio-economic-water-ecological environment system,and to alleviate the contradiction between agricultural water and ecological water has become a key scientific problem to be solved urgently.This study explored the concept and connotation of the suitable agricultural scale,and systematically analyzed the the interaction between water-soil resources,ecological economy and agricultural scale.A scale research system for suitable agricultural based on ecological health and water-saving high efficiency was proposed.As a result,the agricultural suitable scale,agricultural optimal structure and agricultural efficient spatial pattern were constructed.The model was applied in the middle reaches of the Heihe River basin,which is the typical oasis in the northwest China.The contents and conclusions include:(1)A research system for suitable agricultural scale based on ecological health and water-saving high efficiency was constructed.Based on the analysis of the interaction relationship in the oasis water-soil resources,ecosystem-economic and social complex system,a research system for oasis suitable agricultural scale aiming at efficient use of water resources and oasis ecological health was established.The research system proposed the characteristics of“suitable agricultural scale”with“three-dimensionality”.The first one is“suitable quantity”,which determine the scale of suitable agricultural development of ecological health from the perspective of theoretical analysis and practical application by determining the quantitative representation of oasis ecological health;the second is“suitable structure”,that is,the planting structure optimization.From the purpose of cost-effective and efficient water-saving optimization,the optimal development structure of suitable agricultural scale was determined;the third is“suitable space”,that is,the spatial optimization of crop planting structure,with the results of planting structure adjustment and crop planting suitability maximizing,an efficient spatail development model of oasis suitable agricultural scale was obtained.(2)A suitable agricultural scale model based on ecological health was constructed,and a suitable agricultural scale in the middle reaches of the Heihe River basin was determined.By determining the quantitative representation of oasis ecological health,the suitable agricultural scale based on ecological health was determined from the perspective of theoretical analysis and practical application.Firstly,from the theoretical aspect,a suitable agricultural scale model based on the oasis ecological health assessment and sand dynamics principle(SASM-EHA)was constructed.From the practical aspect,a suitable agricultural scale calculation model based on the oasis circle structure and the results of oasis desertification land remediation field test(SASM-OCT)was constructed.The feasibility and rationality of SASM-EHA model were verified by the result of theoretical research and field experimentation.The results show that the calculation of suitable oasis scales in the middle reaches of the Heihe River basin based on SASM-EHA and SASM-OCT are2079~2458 km~2 and 2059~2387 km~2,respectively;and the suitable agricultural scales are1663~1967 km~2 and 1642~1921 km~2,respectively.The results of two methods are basically close.Therefore,the SASM-EHA model can provide a method for other oasis areas without field test data in northwestern of China.According to the calculation of SASM-EHA model,the agricultural scale should be reduced 210 km~2 in 2015,and the scale of the eco-protection system in the middle reaches of the Heihe River should be controlled above 20%to ensure the ecological health of the oasis system.(3)An agricultural cropping pattern optimization model based on water-saving high efficiency was established,and the optimal planting structure under different hydrological years and crop price fluctuation were obtained in the middle reaches of the Heihe River basin.An agricultural cropping pattern optimization model was established,aiming to maximize agricultural net benefit per unit of irrigation water and maximize agricultural net benefit per unit of irrigation area.The irrigation water-saving potential was quantified by assuming an increase in the rate irrigation water-saving of 10%and 20%.Meanwhile,considering the crop planting structure is also influenced by market economic behavior,the impact of price fluctuations is studied.Results showed that the grain crops and cash crops in the middle reaches of the Heihe River should be reduced,and the forage planting area should be increased.The net profit of agriculture increased 0.52×10~8 RMB,and agricultural water consumption reduced 1.02×10~8m~3.The price fluctuation of food crops has little impact on planting structure,and the impact of economic crop price fluctuations on planting structure is obvious.When the irrigation water-saving rate was assumed to increase by 10%,then the water-saving quantity would be 2.63×10~8m~3,and when the irrigation water-saving rate was assumed to increase by 20%,then the water-saving quantity would be 3.08×10~8m~3.The reduced agricultural water can be used to make up for the shortage of ecological water,or restore the groundwater balance.“water-saving ecological compensation mechanism”was proposed,which means the development of high-efficiency and water-saving agriculture should work together with the ecological compensation mechanism,to avoid the“the paradox of irrigation efficiency”.(4)A Spatial optimization of planting structure based on cross-entropy method was established,and the spatial optimal layout of maize and wheat in the middle reaches of the Heihe River basin was obtained.An integrated optimization model was developed for the spatial distribution of agricultural crops.The model is based on the spatial distribution of crop suitability,spatial distribution of population density,and agricultural land use data.Multi-source remote sensing data are combined with constraints of optimal crop area,which are obtained from agricultural cropping pattern optimization model.Using the middle reaches of Heihe River basin as an example,the spatial distribution of maize and wheat were optimized by minimizing cross-entropy between crop distribution probabilities and desired but unknown distribution probabilities.Results showed that the comprehensive suitable area distribution of maize is approximately in accordance with the distribution in the present situation;however,the comprehensive suitable area distribution of wheat is not consistent with the distribution in the present situation.Through optimization,the high proportion of maize and wheat area was more concentrated than before.The maize area should be reduced in Linze County and Gaotai County,and the maize area in Ganzhou should be increased.The wheat area mainly concentrates in Ganzhou District and Linze County,and the wheat area in Gaotai County should be reduced.The outcome of this study provides a scientific basis for farmers to select crops that are suitable in area. |
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