Study On Optimal Irrigation Index Of Soil Water For Cucumber At Different Growth Stages

Soil moisture status is a major factor influencing crop production, and the irrigation is an important measure for the field crops soil moisture supply. Meanwhile for facility agriculture, irrigation is the only way for crops to get water. In this paper, morphological indexes, physiological indexes, yield, fruit quality and water use efficiency of cucumber were studied under the different soil moisture treatments during different growth stages in pot experiment by simulation of drip irrigation. Proper water moisture irrigation maximum and minimum during different growth stages were determined through the analysis of water consumption and the water production function of cucumber, which provided scientific and reliable irrigation parameters for the intelligent irrigation control system of cucumber in greenhouse. The conclusions are as follows:1) The effect of different water treatments on morphological indexes of cucumber during different growth stages showed that: The irrigation minimum during initial bloom stage could be appropriately lower, 55% field water capacity was the suitable soil moisture. Moderate water stress in initial bloom stage, which could promote root development and expand the untilization range of soil moisture of cucumber roots, was of benefit to improve soil water use efficiency and promote the plant height growth later to some extent. Plant height compensation benefit was obvious after irrigation recovery. Moderate water deficit during every growth stage was conducive to the growth of stem diameter, and the higher soil moisture during early-fruit stage was favored for the growth of leaf area. while the lower irrigation limits during mid-fruit stage could reduce the growth of leaf area.2) The effect of different water treatments on physiological indexes of cucumber during different growth stages showed that: during the whole growth stage, the transpiration rate and stomatal conductance increased with the increase of the photosynthetic rate, which showed the same variation with photosynthetic rate. The diurnal course of physiological indexes of cucumber displayed single peak in initial bloom stage and mid-fruit stage, and got the maximum at 12:00, while the diurnal course of physiological indexes of cucumber displayed in a double-peak pattern curve in early-fruit stage, and showed obvious "midday depression " in 12:00. The double peaks of physiological indexes appeared at 10:00 and 14:00 respectively, the peak value of photosynthetic rate at 14:00 was slightly larger than that at 10:00, while the peak of stomatal conductance and transpiration rate at 14:00 were much larger than the peak at 10:00. The lower irrigation minimum during initial bloom stage and early-fruit stage favored the promotion of photosynthetic parameters of cucumber, while the higher or the lower soil moisture during mid-fruit stage could reduce photosynthetic parameters, 75~90% field water capacity was the suitable soil moisture, which reached the maximum of photosynthetic parameters.3) The cucumber fruit quality under different irrigation limits treatments during different growth stages showed the same variation. All the indexes increased with the decreasing of the irrigation minimum during different growth stages. This meant that moderate water deficit by controlling the water supply could improve the fruit quality. The shoot biomass, root biomass and root biomass and shoot biomass ratio under different treatments during different growth stages increased with the decreasing of the irrigation minimum. From the relationship between plant height and root biomass, root biomass/shoot biomass, the root biomass, root biomass/shoot biomass under different treatments during initial bloom stage and early-fruit stage increased with the increasing of plant height, indicating that the growth of aboveground and underground parts had the same variation.4) The treatment maintaining the soil moisture 55~90%, 75~90% and 75~90% field water capacity at initial bloom stage, early-fruit stage and mid-fruit stage respectively (Treatment A3) could not only meet the needs of water consumption in the whole growth period of cucumber but also get the best yield and water use efficiency, and then achieve the dual objectives of high yield and high efficiency at the same time. The cucumber water consumption throughout the whole growth period increased flatly at first then steeply, which was consistent with the demand of cucumber growth and development for water. The amounts of water consumption at initial bloom stage was lower than that at early-fruit stage, and the highest water consumption amount was at mid-fruit stage. And the difference among the daily water consumption under the different water treatments were more and more apparent with the extending of the growth period.5) Water sensitivity indices calculated by the Jensen model using Genetic Algorithm went down successively from mid-fruit stage, early-fruit stage to initial bloom stage, and the water sensitivity indices were 0.635, 0.290, 0.275, respectively. The water sensitivity indices at mid-fruit stage was the highest, which meant that if soil moisture during this growth stage was lower or soil water was deficit, it would have a great impact on the final yield. The water sensitivity indices at initial bloom stage was the smallest, indicating that the moderate water deficit during this growth stage had little effect on the later yield, and appropriate water deficit was allowed in a short time at initial bloom stage. The early-fruit stage was the crucial period from the vegetative growth to reproductive growth of cucumber, water requirement was increasing, the appropriate water stress had no great impact on the final yield of cucumber.6) The morphological indexes, physiological indexes, fruit quality, water use efficiency, shoot biomass, the dry root weight and root-top ratio under treating 90% field water capacity as soil water irrigation maximum were all better than that under 100% field water capacity treatment. Although the yield of per-plant under treating 90% field water capacity as soil water irrigation maximum decreased by 0.9% compared with that under 100%, the water use efficiency increased by 16.84%. So the treatment of 90% field water capacity as soil water irrigation maximum was more reasonable than other treatments.7) For the (spring and summer) cucumber in greenhouse, the irrigation minimum during initial bloom stage, early-fruit stage and mid-fruit stage were 55%, 75% and 75% field water capacity respectively. The appropriate soil water irrigation maximum in the whole growth should be 90% field water capacity.