Abstract:It is significant to explore planting alfalfa on process of the water consumption and salt changes in fields. Taking alfalfa field as the research object and the corn field as the control, the variation of leakage, groundwater recharge, evaporation and transpiration in fields of alfalfa was analyzed. Stable hydrogen and oxygen isotope was used to analyze of the contribution rate of each potential water source, and the changes of salt in the soil was analyzed. The results showed that the total water consumption of alfalfa fields was increased by 20.17%, evapotranspiration ratio was decreased by 66.64% on average. among which the evaporation was decreased by 6.21%, the transpiration rate was increased by 35.80%, the variation of soil water storage was decreased by 8.08%, the leakage was reduced by 39.68% and the supply of groundwater to crops was increased by 153.45%. Relative to corn field, the change of soil volumetric water content was divided into severe fluctuation phase and linear decline phase in 0~100cm soil layers during the growing period. In July, alfalfa field change of soil volume and water content in 0~60cm presented a “U” shape, and the change of soil water content in 0~60cm soil of corn field showed type of “V”. The average soil moisture of 0~30cm in alfalfa field was more evenly distributed than that in corn field during the growing period. There was no clear bias in the absorption, utilization of soil water, irrigation water and groundwater in alfalfa field. However, the water use of maize farmland was biased, and the soil water in soil layer of 0~40cm was mainly used in each potential water sources. By studying soil water in soil layer of 0~100cm at different times, it was flexible to use soil water in a certain soil layer of 0~40cm in the different periods of alfalfa farmland. The corn farmland mainly used water in 30~40cm soil. During the growing period, the average desalting rates of 0~100cm in alfalfa field and corn field were 53.90% and 12.43%, respectively. The absolute difference values of soil salt were 0~0.06mS/cm and 0~0.13mS/cm of soil conductivity in 10~30cm and 30~60cm in the alfalfa field and corn field respectively. The soil conductivity of 10~60cm in the alfalfa field was relatively concentrated and more evenly distributed compared with the corn field. In May, except for 0~10cm and 30~40cm soil layers of the alfalfa field were in a state of salt accumulation and the average rate of change of soil storage salt was smaller than that of corn farmland. From June to August, the soil conductivity of 0~100cm in alfalfa field was larger than that in corn farmland, which was in the state of salt accumulation. In September, the overall soil salinity of different soil layers in the alfalfa field was in a desalted state, and the maximum salt storage rate of the soil was -15.31%.As the depth increase, the change of soil salinity was increased first, and then tended to be stable. However, the overall soil salinity of the corn field was in a salt accumulation state. The change rate of soil salinity was the largest in 80~100cm soil. Therefore, replanting alfalfa was beneficial to enhancing the groundwater use, reducing evapotranspiration ratio, and inhibiting soil salinity. Changing and increasing forage yield (feeding) and developing alfalfa planting was beneficial to the local salinization of fields.
