Abstract:

【Objective】In order to protect the ecological environment of China’s alpine desert steppe and guide the comprehensive and sustainable development of grassland pastoral areas, this study took the alpine desert steppe as the research object, and the optimization simulation calculation and dynamic balance analysis of grassland and livestock were carried out. 【Method】In this paper, based on the characteristics of seasonal rotational grazing and livestock production rhythms, the spatial and temporal segregation of grassland resources and the dynamic changes in livestock numbers were considered, and the two pasture grazing time periods of warm season and cold season were refined. On the basis of the existing reasonable livestock carrying capacity calculation method, the maximum livestock carrying capacity was the goal, the dynamic grass-livestock balance was the constraint, and the turnout time and slaughter rate were the optimization parameters. A grazing-management optimization model was established, and the Ulan County Pastoral area of Qinghai Province was selected as the typical representative of alpine desert seasonal pastoral area. Based on the genetic algorithm optimization, the optimal grazing conditions under the three precipitation scenarios of wet, normal and dry in the pastoral area of Ulan County were determined, a simulation to optimize the forage-livestock balance and dynamic forage-livestock balance analysis was carried out, and then the results with those before optimization were compared. 【Result】 The simulation results of the grazing-management optimization model were better for different precipitation scenarios in the grazing area. Based on the lowest amount of unutilized forage, the optimal grazing conditions under the three precipitation scenarios of wet, normal and dry in the pastoral area of Ulan County were determined to be the transition of livestocks on November 1 with a slaughter rate of 43.4%, the transition of livestocks on November 3 with a slaughter rate of 38.2% and the transition of livestocks on November 3 with a slaughter rate of 36.7%, respectively. The optimal proper carrying capacity was 1.099 million sheep unit, 0.961 million sheep unit and 0.836 million sheep unit in high, normal, and low flow years, respectively, which were 11.75%, 10.44% and 10.43% higher than the proper carrying capacity before optimization, respectively. In addition to the livestock slaughter rate and the transition time, the precipitation was also an important factor affecting the proper carrying capacity in pastoral areas. Before and after optimization, the proper carrying capacity of Ulan County’s pastoral area in wet years was 0.983 and 1.099 million sheep unit, respectively, which was 30% higher than the proper carrying capacity of 0.757 and 0.836 million sheep unit in dry years, respectively. Through the analysis of pasture grass production process and livestock dynamic grass demand process, the dynamic grass-livestock balance calculation for the normal flow year in the pasture area of Ulan County was found that the available forage in the cold season pasture before optimization could not be fully utilized, the grazing process was unreasonable, and the surplus grass amount was more than 61.3 million kg, while after optimization, the problem of underutilization of available forage was effectively solved and the forage resources were efficiently utilized. For the whole grazing area of Ulan County, the adjusting grazing turnout time and livestock slaughter rate was a reliable way to improve the grazing system. The grazing-management optimization model was used to optimize the grazing process in the grazing area, which could ensure the high proper annual carrying capacity in the grazing area while being able to achieve a dynamic grass-livestock balance in the seasonal grazing area. 【Conclusion】The grazing-management optimization had the good applicability to alpine desert seasonal pasturing areas and had the certain superiority in the regulation of grazing management process and the optimization of forage-livestock balance in rotating pastoral areas. The grazing-management optimization model could effectively regulate the livestock carrying capacity of a grazing area, and its optimization results could provide reference for the development of a reasonable grazing system. Therefore, the model could be used to optimize the grazing process of a single herding household or ranch, to obtain the optimal grazing conditions for a single herding household or ranch, so as to develop the corresponding grazing system, which was more practical guidance and operability for the production practice of a single herding household or ranch.

Key words: model, seasonal rotational grazing, dynamic forage-livestock balance, grazing management process, Ulan County