Effect Of Drip Irrigation Frequency On Growth And Yield And Quality Of Watermelon Under Regulated Deficit Irrigation In Plastic Greenhouse

With the area of facility watermelon cultivation continuously expand and the increasing shortage of water resources, study on reasonable irrigation system and the implementation of water-saving irrigation in watermelon cultivation has become an important topic in the development of watermelon industry. The method of taking the evaporation from water surface of evaporation dish as a parameter to estimate crop water requirement has been widely used in vegetable production and can precisely guide irrigation of vegetable. According to the results of preliminary greenhouse watermelon water requirement rule test,the experiment used a method which was a diameter of 20 cm evaporating dish water surface evaporation control irrigation water. By this method the study set up three different levels of irrigation cycle, which were high frequency(Once every 2 days), intermediate frequency(Once every 4 days) and low frequency(Once every 6 days),thus made it be as a 4 factors 3 levels orthogonal experiment design with a total of nine treatments. And each treatment was kept at a same total irrigation amount with 0.4Ep during seedling period, 0.8Ep during flowering fruit-bearing period, 1.6Ep at fruit enlargement period, 0.8Ep at mature period, respectively. The various environmental factors and different irrigation frequency of soil moisture content and soil surface water storage was measured in the experiment. Also, the plant morphological index, physiological index, photosynthetic indexes, fruit quality index, fruit yield and water use efficiency was annalized in the experiment. The results are as follows.(1) In the whole growth period of watermelon, the temperature was between 20~30℃, the humidity was maintained at 42.4%~71.2% during the daytime and the nighttime humidity was maintained at 80.2%~91.8%. The average daily evaporation was 2.9 mm in the greenhouse. This condition could maintain the suitable environmental conditions for growth and development of watermelon. The total amount of evaporation of watermelon during the whole growth period was 207.7 mm, the total irrigation amount was 209.84 mm, the ratio is closer to 1:1.(2) In the whole growth period, the soil volume moisture of each measurement point showed increases first and then decreases and was consistent with the amount of irrigation. The volumetric water content from the drip tape 10 cm was greater than the volumetric water content from the drip tape 20 cm. The volumetric water content was higher under high frequency of irrigation treatment in 7.5 cm deep soil layer. Also, the volumetric water content was higher under low frequency of irrigation treatment in 20 cm deep soil layer. But the soil volume water of different treatment had no obvious regularity in each growth period. Due to the different factors just liked irrigation amount, irrigation frequency and the permeability of soil moisture, the volumetric water content had no significant regular changes under the 0~20 cm surface soil.(3) In all the treatments, T4 seedling medium frequency, flowering fruit-bearing stage high frequency, fruit enlargement period intermediate frequency and low frequency irrigation the mature stage displayed the best growth potential in plant height, stem diameter, single leaf area and number of leaves and kept the suitable level of cell sap concentration and cell water metabolism. Under T4 treatment, the plant was in suitable water metabolism, grew well and strong, which could resist cold injury and other adversity stress in early spring. Meanwhile, T4 had a relatively high level at chlorophyll content, net photosynthetic rate, transpiration rate, stomatal conductance and leaf water use efficiency, this high ability of photosynthesis assimilation in turn contributed to the fruit.(4) In the aspect of fruit quality, T4 had the thinnest peel, which was only 8.30 mm and increased the edible part. Also, T4 had a higher content of total vitamin C, which were reach to 14.10 mg/kg and much the highest center total soluble solid content, edge total soluble solid content as well as soluble protein, which were reach to 12.85%, 10.80%, 0.35 mg/g respectively, in addition, T4 had the lowest center hardness and edge hardness, which were reach to 0.58 kg/cm2, 1.15 kg/cm2, and the whole fruit sweetness was high and had a better quality. Therefore, watermelon had the optimal quality under T4 treatment.(5) In the aspect of fruit production, T4 treatment also had higher fruit rate, single fruit weight and had the highest total fruit production and the highest water use efficiency, which reached to 63.72 t/hm2 and 303.64 kg/(hm2·mm). Besides, T4 had the highest water use efficiency(iWUE), which were reach to 303.64 kg·hm-2·mm-1.Therefore, considering the growth potential, yield, quality and irrigation water use efficiency, this test determined that T4 is the best irrigation frequency plan for the whole watermelon growth period, that is a once every 4 days water irrigation at seedling stage, once every 2 days water irrigation at flowering fruit-bearing stage, once every 4 days water irrigation at fruit enlargement stage and once every 6 days water irrigation at the mature stage. T4 is the best treatment in all the nine treatments and the best irrigation frequency scheme for watermelon irrigation in greenhouse under regulated deficit irrigation in early spring of the northwest region. The research could offer a theory and technology reference to implement water-saving irrigation facilities watermelon cultivation efficiency in the spring of northwest.