Calculation method of livestock carrying capacity of irrigation forage grassland in arid area

Abstract: Water is the key factor to in management of grassland and livestock balance in arid area. The effective way of management is to achieve a balance of supply and demand for water forage grass and livestock. This balance consists of three parts: forecasting the forage grass yield by the water balance theory, planning the livestock carrying capacity related to the forage grass intake and drinking water consume, and estimating the optimal number of livestock husbandry under the coupled limitation of the available forage grass intake carrying capacity and the available water resources quantity. There are some inaccuracy problem in applying traditional carrying capacity calculation method, such as the yield forecasting of forage grass and livestock intake feeding. The objective of this paper was to build a new livestock carrying capacity calculation model based on water-grass-livestock balance. Using Damao county in Inner Mongolia Autonomous Region as research area, we analyzed the curve of water productivity under the different rainfall and irrigation conditions, and forecasted the yield of silage corn by water productivity curve. The irrigation experiment of silage corn under different water condition and different precipitation revealed that there was a non-linear relationship between the water productivity and the sum of precipitation and irrigation. Increasing the sum of precipitation and irrigation can promote the water productivity, but excessive supplying from precipitation and irrigation may lead to a reduction of crop water use efficiency. Based on analyzing the curve of water productivity, the experiment result suggested that the highest water productivity was 12.42 kg/m3 water which achieved with 550 mm water from both precipitation and irrigation. Precipitation was the vital limited factor for silage corn yield. The calculated silage corn yield of humid, medium and arid scenario was 6.83 kg/m2, 5.25 kg/m2, 3.47 kg/m2 respectively. For livestock intake feeding and drinking water, carrying capacity of available grass intake and the carrying capacity of available drinking water were calculated respectively, and the minimum values of the two carrying capacities were used to determine the proper livestock carrying capacity. The results showed that the carrying capacity of water, forage grass and livestock balance model was six sheep more per 10 000 m2 than the tradition method in humid scenario. The increasing number of livestock was good for improving the economic benefit for farmers of animal husbandry. Under the arid scenario, the carrying capacity of water, forage grass and livestock balance model was seven sheep less per 10 000 m2 than the tradition method. The decreasing number of livestock was beneficial for the ecological and environmental protection of grassland. In conclusion, the water, forage grass and livestock balance model proposed by the paper was appropriate for arid grassland, and it will have much impact on the development of livestock husbandry and the protection of ecology and environment in pasture area.