Optimization of the planting structure in the upstream region of Baiyangdian Lake based on the non-dominated sorting genetic algorithm (NSGA-Ⅱ)

Reasonable planting structures are the basis of the optimal allocation of regional water and land resources. The upstream region of Baiyangdian Lake suffers from the perils of water shortage and an unreasonable planting structure. On the base of the current status of the main crop planting structure, this study considered the crop planting area as optimization variable, the water resources, land resources, and social needs as the constraints, while seeking to maximize the economic and ecological benefits and to minimize the irrigation water consumption based on the non-dominated sorting genetic algorithm (NSGA-Ⅱ) of the crop planting structure adjustment model. This study also proposed the planting structure optimization schemes under different scenarios of various water restrictions and agricultural mechanization levels in the mountain area and plain area of the upstream of Baiyangdian Lake. The results showed that, at the current status of mechanization level, the area of the rotations of two crops in a year scaled down, while vegetables and mung beans-fresh maize areas increased, the economic benefits should increase 12.6%, and ecological and water-saving benefits decreased under the no-restricted irrigation water; while wheat-maize, mung beans-fresh maize, spring sweet potato, vegetables and fruits areas increased under restricted irrigation water inducing increased economic and water-saving benefits. In the 20% water-saving scenario, almost all crop areas would be scaled down, including vegetables, area of wheat-maize decreased 21.5%, and economic and ecological benefits decreased. In the scenario without water limitation, the optimized economic benefit increased the most, the ecological benefit decrease the least, water consumption increased, and the grain yield decreased the least. However, in the scenario of 20% water saving, the economic and ecological benefits and grain yield decreased. Under current and future mechanization levels, the fruit tree area increased under different water restriction scenarios. With no-water limitation, the economic and ecological benefits maximally improved after optimization, and water use and grain yield maximally decrease. Under the 20% water-saving scenario, the economic benefit increased the least, the ecological benefit decreased, and grain yield decreased the most. These results indicate that the current and future mechanization scenarios are not limited by water in the plain or mountainous areas, and the optimized economic and ecological benefits are relatively high. Moreover, in the plain areas with low water-saving requirements, the vegetable planting area should be increased, and the grain planting area should be reduced. In areas with high water-saving requirements, the planting area of all crops, including fruits and vegetables, should be reduced. In the mountainous areas, the grain planting area should be reduced, and the fruit tree planting area should be expanded. This study provides a decision basis for future regional planting structure adjustment. Past adjustments in the planting structure, with more adjustments according to different crop types, tended to ignore adjustments in the different cropping systems or to consider the fixed number of years or different climate scenarios. This paper proposed different scenarios of mechanization and water limitations and highlighted the optimization results under different scenarios for similar areas after adjustment in the planting structure.