Water-saving Mechanism Of Regulated Deficit Irrigation Of Eggplant In Sunlight Greenhouse

A field plot experiment was conducted to study the efficient irrigation index and irrigation scheduling with water-saving, high yield, and high-quality for eggplant in sunlight greenhouse. Taking the "Xinxiang green eggplant" as a test material, this research was carried out in a greenhouse with drip irrigation system at experimental station of crop water requirement in Farmland Irrigation Research Institute of CAAS from March to July in2011. The effects of different degrees of regulated deficit irrigation on plant growth, physiological characteristics, final yield, fruit quality, water consumption law and water use efficiency of eggplant were studied. The main results were as following:(1) The plant height, stem diameter and leaf area index of eggplant showed such a law as slow at the seedling stage, rapid growth at the early flowering-fruit bearing stage and growth slowdown and tended to be stable (but leaf area index tended to decrease) at the fruit maturation stage. The eggplant morphological indexes were different when different water deficit occurred at different growing stages. In the view of the eggplant growth situation, slight water deficit at the fruit maturation stage should be taken, which did not affect the normal growth of eggplant and also inhibit plant excessive growth so as to provide a good base for yield formation with water-saving.(2) At the flowering-fruit bearing stage of eggplant, the diurnal variation of photosynthetic rate, transpiration rate, stomatal conductance and cell sap concentration showed a single peak curve under different regulated deficit treatments. Each physiological index has close relation with water deficit, slight water deficit had small effect on photosynthetic rate, transpiration rate and stomatal conductance, while severe water deficit significantly inhibited photosynthetic rate at any growing stage. The physiological compensation of transpiration rate and stomatal conductance was evident due to re-watering after water stress. Water deficit could improve cell sap concentration, the degree of improvement was proportional to the degree of water deficit and the cell sap concentration decreased when re-watering after water stress. In addition, the photosynthetic rate and cell sap concentration at the flowering-fruit bearing stage were greater than that at the fruit maturation stage, but opposite for transpiration rate and stomatal conductance. In the view of the physiological characteristics of eggplant, slight water deficit at any growing stage should be adopted in irrigation management.(3) Slight water deficit at the seedling stage decreased the percentage of malformed fruit and increased the fruit size, at the same time, it could increase fruit yield and promote fruits to mature early. Eggplant was sensitive to water deficit at the flowering-fruit bearing stage, water deficit decreased fruit numbers, reduced fruit size and led to great reduction in yield at this stage. Slight water deficit occurred at the fruit maturation stage could increase the fruit numbers of eggplant and fruit size, decrease the percentage of malformed fruit, promote early maturity, and finally improve the yield and economic benefits greatly. Severe water deficit could improve the contents of soluble sugar, soluble protein and soluble solids obviously at any stages, but decreased fruit yield. Slight water deficit could also improve various indexs of fruit quality. Comprehensively considering the effects of regulated deficit irrigation on the yield and quality of eggplant, the measure of implementing slight water deficit at the seedling stage and the maturation stage should be taken, but full irrigation should be adopted at the fruit maturation stage.(4) The change of soil evaporation presented a pulse-shaped curve in the whole growth period of eggplant, and it was high at the earlier stage and became lower gradually at the later stage. Meanwhile, the soil evaporation showed an exponent function relationship with leaf area index, and a polynomial function with surface soil moisture. The water consumption and consumption intensity of eggplant increased with the advance of plant growth stage, and reached the maximum at fruit maturation stage. Water depletion of eggplants was largely related to water deficit, namely, continued or increasing water deficit decreased the total water depletion and stage water consumption. Water deficit can increase water use efficiency (WUE) of eggplant, but it is not suitable to implement water deficit at the flowering-fruit bearing stage. At the same time, severe water deficit at the seedling stage and flowering-fruit bearing stage led to yield reduction. Slight water deficit at seedling stage and fruit maturation stage could gain both high yield and high efficiency in the case of increasing WUE.(5) Through considering comprehensively the response of growth situation, physiological characteristics, yield, quality, water consumption law and water use efficiency of eggplant to different degrees of regulated deficit irrigation at different growing stages, a regulated deficit irrigation model was study tentatively established of eggplant with drip irrigation to aim for water saving, high yield and high efficiency, which was that the irrigation cycle was10d, and appropriate water deficit should be applied at seedling stage and fruit maturation stage with irrigation quota of12mm and20mm, respectively, and full irrigation should be adopted at flowering-fruit bearing stage with25mm irrigation quota.