Soil water storage deficit of alfalfa (Medicago sativa) grasslands along ages in arid area (China)

Alfalfa (Medicago sativa) is a high-yield and high drought-tolerant perennial forage crop, which take up water from deep soil layers by its deep root system. Long-term cultivation of alfalfa without a sufficient water supply aggravates soil water storage deficits, which are not conducive to plant succession. In this study, we studied the above-ground biomass and the degree of soil water storage deficit at different alfalfa stands of different planting ages. The experiment was conducted in six alfalfa grasslands of different ages. Soil water content of the 0–300 cm soil layer in each grassland was measured for the calculation of soil water storage deficit. The results showed that soil water storage increased gradually along the soil profile. The degree of soil water storage deficit was the highest in all six alfalfa grasslands at the depth of 0–150 cm. The deficit degree of the one- and six-year-old alfalfa grasslands was significantly higher than that at the grasslands that had been cultivated for two to five years (P < 0.05) at the depth of 0–100 cm. The deficit degree of the four- and five-year-old alfalfa stands was less than 10% below the depth of 200 cm. The above-ground biomass reached a peak value in grasslands that had been cultivated for three and four years, and then gradually decreased. In summary, based on its relatively high yield and low soil water consumption intensity, the optimal cultivation age for alfalfa grasslands was four years. Thus, irrigation should be increased after five years’ cultivation of alfalfa. Moreover, more water should be supplied to the upper soil layer of one-year-old alfalfa grassland stands. This study provides the basis for water management measures of alfalfa grasslands in arid areas.