Research Of The Effects And Water Use Feature On Alfalfa Mixed Sowing With Graminaceous Crops In Ningxia Central Arid Zone

Ningxia central arid area is characterized by low vegetation coverage and fragile ecological environment, because of low rainfall in this area. Planting perennial feeding crops with drought resistance is environmental-friendly. Mixed sowing of leguminous and graminaceous crops can improve the yield per unit area, soil nutrient and the quality of forage. Experiments of mixed sowing between leguminous and graminaceous were carried in simulated water treatment conditions and field trial. In pot experiment 1, there were three water treatments, i.e. severe water stress(T1,45% Field Capacity, FC), moderate water stress(T2,55% FC) and well watered(T3,75% FC). Two leguminous crops, i.e. Medicago sativa and Astragalus adsurgens, one graminaceous crops, i.e. Elymus dahuricus were planted in three ratio, i.e. legume:gramineae as 3:7,5:5,7:3. In pot experiment 2, two leguminous crops, i.e. Medicago sativa and Astragalus adsurgens, one graminaceous crops, i.e. Secale cereale L. were planted in a split-root pot experiment in three ratio, i.e. legume:gramineae as 3:7,5:5,7:3. In field experiment, two leguminous crops, i.e. Medicago sativa and Astragalus adsurgens, two graminaceous crops, i.e. Leymus chinensis and Elymus sibiricus were planted in three ratio, i.e. legume:gramineae as 3:7,5:5,7:3. Then, yield, the ash content of whole plant, carbon isotope discrimination (△13C) of whole plant, photosynthesis parameters and other physiological characters were measured. The relative total mixed combinations (RYT), competitiveness (CR), agronomic water use efficiency (WUE), single leaf water use efficiency were calculated. Hydrogen isotope compositions (δD) of xylem sap of leguminous and graminaceous crops and soil water were analyzed for determining the hydraulic lift effect. There are several main results as follows:(1) In pot experiment 1, yield and WUE of different mixed sowing combinations were significantly different in different water conditions. Yield under well watered condition was highest. Yield for the mixed combination between alfalfa and elymus was higher than that between adsurgens and elymus in the same proportion. The highest water use efficiency was found in moderate water stress treatment. Under the same water conditions, WUE of combinations increased when the proportion of leguminous crops increased. Slight water stress could increase crop WUE.(2) There are significant correlations between yield, A13C of plants and photosynthetic parameters in different mixed sowing combinations. There is a certain correlation under the different water conditions. Less than three soil moisture conditions the yield are negatively correlated A13C, under the normal irrigation water negative correlation was significant. Leaf intrinsic WUE had positive correlation with yield under three water treatments. There is a significant positive correlation between plant height and yield, plant height significantly and positively correlated with yield in the T3. The plant height and yield increased with an increase in the soil water content. Ash content in whole plant is negatively correlated with yield.(3) In pot experiment 2, different mixed sowing combinations in the water treatment 3 displayed highest yield among three soil water treatments. The hydraulic lift capacity of legume is highest in the combination of legume:gramineae as 5:5 under the same soil water conditions. The combination of legume:gramineae as 5:5 produced highest yield among there water treatments, moderate drought promoted the hydraulic lift capacity of legume.(4) In field experiment, yield was attected significantly by mixed sowing proportion. The combination of alfalfa and Leymus chinensis with ratio of 7:3 had highest yield, crude fat yield, protein yield and highest WUE under the same soil water conditions.