Effect of paddy dew on rice growth

Dew, a crucial element of water cycle in farmland ecosystems, plays an important role in water and nutrient balance in paddy field. As a form of wet deposition, dew is a major pathway for the flow of acidic pollutants from the atmosphere to the biosphere. Acidic dew can damage protective surfaces of leaves, interfere with guard cells and poison plant cells. With dew as a surfactant by nutrient adherence to leaves, recognition of dew as an important factor of nutrient uptake is particularly significant. Dew, as a nutrient input, has always been ignored. Identifying the nutrients in dew is necessary to determine the significance of leaf dew in agricultural practices. The goals of this study were to investigate pH and essential nutrients ammonium nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃^--N) and phosphate (PO₄^3--P) in paddy dew and to explore the role of dew in nutrition availability to rice. To this end, in situ dew samples in paddy field were collected from the early July to early October of 2013 at the Sanjiang Plain Paddy Experimental Station (47°35′N, 133°31′E) of Chinese Academy of Sciences. The leaf dew samples were collected 30 min before sunrise on heavy dew days and a total of 22 dew samples were collected directly on rice leaves. A conservative unit area of actual dewfall estimated by LAI in paddy field was 28 mm in 2013. Dew was accounted for 8.3% of total rainfall during the period of study. NO₃^--N concentration in dew was significantly (P< 0.05) greater than NH₄⁺-N and PO₄^3--P concentrations. Based on statistical analysis, pH affected PO43 -P and NH4+-N concentrations of dew in paddy field. Dew contained more NH₄⁺-N, NO₃^--N and PO₄^3--P than rain. pH of dew was in the range of 5.34 7.10 with a mean of 6.37, which was not strong enough to cause damage to rice leaves in paddy field. The higher concentrations of N and P in dew were attributed to dry deposition on wet surfaces and variations in composition at high-altitude (cloud level) and low-altitude (ground level) aerosols and gases, to which the dew and rain were exposed. The contribution of leaf dew to rice growth was limited because of its limited condensation time. The deposition amounts of NH₄⁺-N, NO₃^--N and PO₄^3--P in the 28 mm dewfall from July to October in the paddy field were respectively 0.11 kg·hm^-2, 0.22 kg·hm^-2 and 0.04 kg·hm^-2. Although nutrients were in low concentration in the dew, dew-nutrient supply was long-term. Leaf dew was not temporal, while the foliar fertilizer was evaporative. Thus leaf dew contributed more nutrients to paddy field that subsequently enhanced significant rice growth. The deposition amount of NH₄⁺-N, NO₃^--N and PO₄^3--P of dew were about 100 times as much as that of foliar fertilization. In addition, dew condensation on both sides of the leaf enhanced more effective uptake of nutrients. Therefore N and P in dews in paddy fields were other significant source nutrients. Dew was an important pathway for the nutrient transfer in paddy fields.