Effects Of Different Water Treatments On Yield And Quality Of Drip-irrigated Muskmelon In Plastic Greenhouse

The declining availability of fresh water has become a worldwide problem, especially in China. Water shortage limits the economy development. Irrigation scheduling for crops is very important to water saving. Muskmelon (Cucumis melo L.) is an important horticultural crop in the world, scheduling water application is very critical to make the most efficient use of drip irrigation system. Drip irrigation has many advantages from agronomic, water conservation and economic aspects. This paper consisted of three experiments which consist of different irrigation maximums. different irrigation quantity and different irrigation frequency. The main results were as follows:1. The irrigation water amounts were determined based on the percentage of field water capacity. On the same basis of irrigation start point of 60% (the percent to comparing to the field water capacity), there were four different irrigation water levels 100% (T100), 90% (T90), 80% (T80) and 70% (T70) as the four different treatments. The results showed that plant growth, fruit production and quality were significantly affected under different irrigation water amounts. Plant height and stem diameter decreased as well as fruit yield from treatment T100 to T70. The highest net photosynthetic rate (Pn), transpiration rate (E) and stomatal conductance (Gs) reached at T90, and the fruit quality was the best in the T90 treatment. The irrigation water use efficiency (IWUE) values found in this experiment showed that the lower the amount of irrigation water applied, the higher the irrigation water use efficiency obtained. Hence, based on the quality and quantity of muskmelon yield, the regime for 90% of field water capacity is the suitable soil irrigation treatment which can save irrigation water and improve the quality of fruit.2. Application of irrigation water was based on cumulative class A pan evaporation within the irrigation interval 2-3days, treatments consisted of four pan coefficients (K1.2, 1.20; K1.0, 1.00; K0.8, 0.80 and K0.6, 0.60). Data showed that the more irrigation water were applied, there were bigger stem diameter and larger leaf area. The amount of irrigation water applied significantly affected fruit quality, K0.8 treatment seems to be the best, but there was no significant difference between K0.8 and K1.0. The more amount of irrigation water applied, the more muskmelon fruit yield can be got. On average, the K1.2 treatment gave the highest fruit yield, whereas K0.6 treatment gave the lowest, fruit yield decreased significantly with decreasing water amount at the treatment K0.8. The irrigation water use efficiency (IWUE) values found in this experiment showed that the lower the amount of irrigation water applied, the higher the irrigation water use efficiency obtained. Combined the yield and quality of muskmelon, Kcp = 1.00 values can be recommended for the most appropriate irrigation scheduling. Therefore, applying water by drip irrigation in relation to the amount of water evaporated from a standard 0.2 m diameter pan is a convenient, simple, easy, and low cost method inside a plastic greenhouse.3. Treatments consisted of four different drip irrigation frequencies: D1 (once every day), D2 (once every 2 days), D4 (once every 4 days) and D8 (once every 8 days), with total drip irrigation water equal for the different frequencies based on a standard 0.2 m diameter pan evaporation. The study results show that high frequency irrigation increase remarkably leaf area and the content of leaf chlorophll, but there is no significant differences about growth among different irrigation frequency treatments. During critical periods, the diurnal variation trends of transpiration rate (E) and stomatal conductance (Gs) of muskmelon had one peak for D1, D2 and D4(D1 at 12:00, D2 and D4 at 14:00), where D8 had two peaks at 14:00 and 16: 00 respectively. Treatments had the highest net photosynthetic rate (Pn) at 10:00, but there was no significant correlation at any time. The effects of irrigation frequency on yield and irrigation water use efficiency (IWUE) were not significant whether one every day or one every eight days. In conclusion, treatment within 2-4-day irrigation interval is recommended for muskmelon growing in plastic greenhouse in order to get higher muskmelon yield, better quality and to save time and labor.