Effect Of Active Water Deficit On Growth And Water-and Nutrient-Use Of Soybean

Study on the effect of active water deficit on crop growth, yield, water- andnutrient- use under different fertilization condition has scientific significance incrop production when treated with active water deficit. This paper deals with theeffect of moderate water deficit on soybean growth, dry mass accumulation, yield,water-and nutrient- use when different water deficit in seedling, branching andpod setting -filling period were treated under different P and K condition,respectively. Four irrigation levels, i.e. severe water deficit (40～50%θ_f,θ_f is fieldcapacity), medium water deficit (50～60%θ_f), slight water deficit (60～70%θ_f) andconventional irrigation (70～80%θ_f), and three PK levels, i.e. P₀K₀ (no PK added),P₁K₁ (0.05g P₂O₅/kg and 0.05g K₂O/kg) and P₂K₂ (0.15g P₂O₅/kg and 0.15gK₂O/kg) are designed during the seedling period. And three water levels, i.e.medium water deficit (50～60%θ_f), slight water deficit (60～70%θ_f) andconventional irrigation (70～80%θ_f), and three P levels, i.e. P₀ (no P added), P₁(0.05g P₂O₅/kg) and P₂ (0.10g P₂O₅/kg) are treated during the branching periodand pod setting-pod filling period, respectively. The main results are outlined asfollow:(1) Before rewatering, both leaf photosynthesis rate and transpiration rate ofsoybean during the water deficit of seedling period reduce with the increasedwater deficit. But after rewatering there are no significant differences in both leafphotosynthesis rate and transpiration rate among different water deficit treatments.Among these water deficit treatments, both leaf photosynthesis rate andtranspiration rate in slight water deficit treatment restore more quickly than those of the other water deficit treatments, so the obvious compensation effect isobserved in the slight water deficit treatment.(2) After rewatering, plant height and leaf area in slight water deficittreatment are greater than those of conventional irrigation treatment in seedling,branching and pod setting-filling period of soybean. But plant height and leafarea in the other water deficit treatments are generally lower than those ofconventional irrigation treatment.(3) After rewatering, dry mass accumulation and seed yield in slight waterdeficit treatment are significantly greater than those of conventional irrigationtreatment in seedling, branching and pod setting-filling period of soybean. Forexample, compare to the conventional irrigation treatment, seed yields in P₀K₀,P₁K₁ and P₂K₂ treatments during the seedling period, and P₀, P₁ and P2 treatmentsduring the branching and pod setting-filling period increase by 0.62%, 5.62%and 33.56%; 14.00%, 7.69% and 36.32% and 47.93%, 8.40% and 25.67%,respectively when treated with slight water deficit.(4) Compare with the conventional irrigation treatment, water use efficiencyon basis of soybean seed (WUE_seeds) treated with the slight water deficit treatmentduring seedling period approachs or exceeds that of conventional irrigationtreatment. And WUE_seeds in P₀ and P₂ treatmeats duringbranching period and in P₀,P₁ and P₂ treatmeats during pod setting-filling period increase by 2.27% and20.60% and 10.64%, 8.33% and 39.51%, respctively. But WUE_seeds in the otherwater deficit treatments are lower than that of conventional irrigation. Thus slightwater deficit can improve the water use efficiency on basis of soybean seed.The above-mentioned results indicate that slight water deficit treatment isbeneficial for the restoration of leaf photosynthesis rate and transpiration rate ofsoybean, thus promotes crop plant and leaf growth and increases seed yield ofsoybean, and finally improves the water use efficiency on basis of soybean seed.Therefore, slight water deficit treatment has the over-compensation effect on soybean growth and yield.(5) Compare with the conventional irrigation treatment, shoot and total N, Pand K uptake of soybean increase when treated with slight water deficit during theseedling, branching and pod setting-filling period of soybean, but soil availableN, P and K content reduce. Thus, slight water deficit are beneficial for absorbingthe available nutrients from soil, thus soil available nutrients content reduce.