Effects of irrigation amount on the rhizospheric environment and stem flow of melon cultivated with full organic nutrition in greenhouse

Abstract: It is of great significance to explore the regulation mechanism of irrigation amount in rhizosphere - stem flow - air environment for the utilization efficiency and for the rational management of water and fertilizer application. The experiment was conducted in the experimental base of Northwest A&F University from April 20, 2018 to July 15, 2018. The melon "Qian Yu-6" was used as the test material using potted cultivation, and irrigated according to 80% (T1), 100% (T2), and 120% (T3) of the daily weighted evapotranspiration (for short as "WET"). Transpiration water consumption was recorded by automatic continuous water consumption recorder, and three plants were placed on each recorder. Sufficient irrigation was carried out on the day before treatment. After the excess water outflow in the basin was completed, the cultivation basin was placed on the weighing recorder. The instrument recorded the mass as W1, and the mass as W2 after 24h, and the WET was the difference between W1 and W2. The instrument was corrected every 7 days. At the same time, the air environment, rhizosphere environment and stem flow of muskmelon were monitored every day, and the relationships among greenhouse air environment, plant stem flow and rhizosphere environment in typical weather were screened and analyzed. The results showed that the transpiration water consumption per plant of T1, T2 and T3 was 0.4, 0.5, 0.6 kg/d, and the maximum stem flow was 0.033, 0.42, and 0.126 kg/h, respectively on a typical cloudy day. The evapotranspiration of T1, T2 and T3 was 0.87, 1.13 and 1.72 kg/d respectively, and the maximum stem flow was 0.075, 0.091 and 0.407 kg/h respectively on typical sunny days. That the variation of stem flow was positively correlated with the variation of irrigation. The maximum rhizosphere temperatures of T1, T2 and T3 were 26.8, 27.4 and 26.2 ℃ respectively on typical cloudy days, and 36.8, 37.8 and 38.5 ℃ respectively on typical sunny days. T2 treatment was beneficial to the improvement of rhizosphere temperature, the increase of stem flow rate and the improvement of rhizosphere water use efficiency. The results showed that the order of the daily changing law of the rhizospheric temperature was T2>T1>T3 on typical cloudy day, while it was T3>T2>T1 on typical sunny day. The ranking order of the daily changing law of the rhizopheric relative water content was T3>T2>T1 during 0:00-14:00 and T3>T1>T2 during 14:00-24:00 on typical cloudy day, and it was T3>T2>T1 on typical sunny day. The order of the rhizopheric conductivity was T1>T2>T3 on cloudy day, but it was T1≈T2>T3 during 0:00-14:00 and T2>T1>T3 during 14:00-24:00 on sunny day. The correlation coefficient between the stem flow rate and the environmental factors on typical cloudy days turned out to be VPD (Vapor Pressure Deficit) > RH (Air Humidity)> Ta (Air Temperature) > Ts (Rhizospheric Temperature) > Rn (Air Radiation) > EC (Rhizospheric Conductivity) > SWV (Rhizospheric Water Content). The correlation coefficient of environmental factors on stem flow was VPD>SWV>Ts>RH>Ra>Ta>EC on typical sunny days. The decision coefficient between stem flow and environmental factors was VPD>Ta>RH>Ts>Rn>SWV>EC on cloudy days and the decision coefficient of stem flow changes was EC>VPD>Rn>Ts>RH >Ta >SWV on sunny days. The results showed that the EC mainly inhibited the "source" of stem flow, while the VPD mainly promoted the "reservoir" of stem flow. The SWV was the limiting factor of stem flow on sunny days. Irrigation of 120% of daily transpiration on sunny days was conducive to maintaining the water balance of melon water transport in the soil-plant-atmosphere Continuum. In summary, the rhizosphere environment and air environment affect the transpiration of melon, which is of reference value for the further study on the management system of water and fertilizer in the cultivation of melon with whole organic nutrition.