| The Western Loess Plateau hilly- gully region is a poverty living areas of rural residents in China. Crop unicast and excessive cultivation is the main reason causing loss of soil and water. At the same time, the reason why agricultural system is unstable is that the large precipitation variability and low production. As good leguminous forage, Lucerne plays an important role in the ecological environment construction and industrial structure adjustment in this area. However, the formation of deep soil dry layer for several years is difficult to recover in a long time. Therefore, in order to explore the C haracterization of evapotranspiration rule and soil moisture restoration of lucerne-crop rotation system after perennial lucerne on Western Loess Plateau rainfed agricultural area. Different forage grain crop rotation system including Lucerne-Lucerne(L-L), Lucerne-Fallow(L-F), Lucerne-Wheat(L-W), Lucerne-Corn(L-C), Lucerne-Potato(L-P), and Lucerne-Millet(L-M). Through the study of crop yield and water consumption characteristics, soil physical properties, temporal and spatial variation of soil moisture for lucerne-crop rotation systern on Loess Plateau rainfed agricultural area, to definite the effect and mechanism of soil moisture restoration for different grain and forage crop rotation system. In order to provide theoretical basis for screening suitable forage grain crop rotation patterns and lucerne land sustainable use for rainfed agricultural area of the loess plateau. The main results are as follows:(1) With increasing of the rotation period, the yield for the treatment of Lucerne-Lucerne and Lucerne-Potato decreased gradually and Lucerne-Wheat increased. Compared with the year of 2013, the yield of Lucerne-Corn, Lucerne-Millet and Lucerne-Wheat was the highest in 2015. The water use efficiency of Lucerne-Lucerne increased gradually with increasing of the rotation period, but Lucerne-Potato decreased gradually.(2) The characteristics of evapotranspiration shows different under different Lucerne-crop rotation system. The water consumption of Lucerne-Fallow is the highest about 294.57 mm, Lucerne-Wheat which is the lowest about 247.11 mm. The proportion between evaporation of total water consumption shows that Lucerne-Fallow is more than 90%, and Lucerne-Corn is only 17%. It further shows that the water consumption of Lucerne-Fallow is mainly used for soil evaporation, and Lucerne-Corn is mainly used for crop transpiration.(3) Through the evaluation about the effect of soil water recovery, soil moisture content in 0~300 cm layer of Lucerne field shows recovery in different degree after 4 years of grain crops rotation. The treatment of Lucerne-Fallow is complete recovery(recovery index 132%). Lucerne-Potato is in excellent performance for recovery(recovery index 96%). Other treatments are in good performance for recovery(recovery index 62%~72%). The treatment of Lucerne-Fallow is the best pattern for soil moisture recovery, and Lucerne-Potato is better than other crop rotations as a whole.(4) Lucerne-crop rotation reduced soil bulk density, and increased soil porosity. Compared with Lucerne- Lucerne, the soil bulk density for the patterns of Lucerne-Fallow, Lucerne-Wheat, Lucerne-Corn, Lucerne-Potato and Lucerne-Millet reduced by 6.86%, 7.69%, 6.22%, 9.29% and 10.17%, the soil saturated hydraulic conductivity for the patterns of Lucerne-Fallow, Lucerne-Wheat and Lucerne-Millet was increased by 0.32, 1.52 and 0.33 time, respectively. It is showed that Lucerne-Millet and Lucerne-Potato significantly reduced the soil bulk density, Lucerne-Wheat and Lucerne-Fallow increased significantly the soil infiltration.(5) Lucerne-crop rotation system all reduced the content of soil water stable aggregates. Compared with the treatment of Lucerne-Lucerne, the content of soil water stable aggregates for Lucerne-Fallow, Lucerne-Wheat, Lucerne-Corn, Lucerne-Potato, and Lucerne-Millet is decreased by 33.44%, 23.08%, 7.36%, 27.09%, and 20.29% respectively. Meanwhile, it is also found that the mechanical stability of soil aggregate gradually increased with the increas ing of soil depth, but the water stability of aggregates decreased.(6) Lucerne-crop rotation reduced the content of soil organic carbon in different extent. Lucerne- Lucerne and Lucerne-Fallow maintained a high soil organic carbon content. Correlation analysis showed that the correlation between the SOC content and 2~5 mm, 1~2 mm, 0.5~1 mm, 0.25~0.5 mm water-stable soil aggregates contents and MWD were significantly positive. The correlation between the <0.25 mm soil aggregate and SOC was significantly negative. |
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