Study Of Rainfall On Nutrient Leaching From Maize Canopy

Plant canopy has an important role in nutrient circulation and changing of flux in nutrient circulation, it is a common scientific issue in plant nutrition and ecology. Nitrogen losses in plant canopy and nitrogen absorption of plants are an important component of soil-plant nutrient circulation system which have same important role on nitrogen utilization and ecosystem nitrogen equilibrium. Therefore, investigate the flux and where it goes of the canopy N losses has great scientific value on further understanding plant N mechanism, equilibrium and improving N utilization.Nutrient loss by leaching is one of the possible ways of nutrient loss from plant canopy, and it is very important for understanding nitrogen equilibrium of farmland ecosystem to research nutrient loss by leaching from plant canopy. Different varieties and treatments of different nitrogen applications in experiment were conducted to study the effect of precipitation on nitrogen leaching from maize canopy by using 15N tracer technique and simulated precipitation. The maize varieties were Xingyu998(X), Yuyu22(Y) and Zhongdan5384 (Z). The nitrogen fertilizations were divided into 0(N0),0.20g(N2) and 0.40g(N4) N/kg soil different nitrogen levels. The main conclusions and innovations were following.1. Result of 15N tracer experiment showed that nitrogen was loss by leaching from maize canopy after precipitation, and the total content of nitrogen leaching from canopy account for the total nitrogen in tasseling stage was higher than in shooting stage. There was no organ nitrogen in leachate from maize canopy. There were NH₄⁺-N and NO₃^--N loss in leachate, and NH₄⁺-N loss was higher than NO₃^--N. Concentration of NH₄⁺-N and NO₃^--N in leachate from maize canopy ascended first and then descended along with the growth. Under the 60mm precipitation, the total NH₄⁺-N leaching was 11194.8μg/plant and the total NO₃^--N leaching was 2979.9μg/plant, and the total nitrogen leaching was 14174.7μg/plant. Concentration and content of NH₄⁺-N and NO₃^--N in leachate decreased along with the extension of time, and were inverse ratio of time There was significant difference of concentration and content of NH₄⁺-N and NO₃^--N between the treatments of different nitrogen applications.2. The total leaching contents of NH₄⁺-N and NO₃^--N of per square meter of leaves and of per fresh weight ascended first and then descended along with the growth. They decreased along with the extension of time, and were inverse ratio of time. There was no significant difference of them between different varieties. Comparing with the treatment of no nitrogen application, the total leaching contents of NH₄⁺-N and NO₃^--N of per square meter of leaves and of per fresh weight decreased gradually with the increase of nitrogen application. There was a significant difference of total leaching content of NH₄⁺-N of per square meter of leaves and of per fresh weight between the treatments of different nitrogen applications, and there was no significant difference of total leaching content of NO₃^--N.3. Characteristics of stomatal, Pn and so on of canopy leaf changed along with the different nitrogen application and varieties during different growth stages, and also were affected by different nitrogen applications. Among the different nitrogen treatments, stomatal frequency descended gradually after applying nitrogen, and stomatal length, width, areas and perimeter of nitrogen application are higher than treatment of no nitrogen application. Pn, Gs, Tr and SPAD of nitrogen application were higher than treatment of no nitrogen application. Ci of leaf descended and WUE ascended gradually after applying nitrogen.The apparent free space (AFS) of leaf descended gradually along with the growth. AFS of shooting stage was the largest, and AFS of maturity stage was the smallest. There was significant difference of AFS between different growth stages. Comparing with AFS of treatment of no nitrogen application (the average was 0.916 ml.g-1 leaf), AFS of N2 treatment descended (the average was 0.858,0.916 ml.g-1 leaf), and AFS of N4 treatment ascended (the average was 1.510,0.916 ml.g-1 leaf).4. Correlation analysis showed that the total leaching content of NH₄⁺-N was positively correlated with Pn and stomatal frequency of leaf significantly. The total leaching content of NH₄⁺-N of per square meter of leaves were negatively correlated with the total nitrogen of stem & leaf, and with the NO₃^--N content of stem & leaf, and with leaf area and fresh weight per plant significantly, respectively. The total leaching content of NH₄⁺-N of per fresh weight was positively correlated with stomatal frequency and Ci of leaf. The more the stomatal frequency was, the more the Pn was, and the more the total leaching content of NH₄⁺-N was. Besides the nitrogen levels, the NH₄⁺-N leaching was affected by plant nutrition and characteristics of stomatal and photosynthetic.Correlation analysis showed that the total leaching content of NO₃^--N was positively correlated with the NO₃^--N content of stem & leave and the water content of stem significantly, and with leaf area and fresh weight per plant greatly significant. There were negative correlations between the total leaching content of NO₃^--N of per fresh weight and the total nitrogen of stem & leaf, and the water content of leaf of leaf significantly. The more the stomatal width was, the more the stomatal areas was, the more the total leaching content of NO₃^--N was. Besides the nitrogen levels, the NH₄⁺-N leaching was affected by plant nutrition.The research indicated that nutrient loss by leaching from canopy increased with the increase of leaf areas, stomatal frequency and the ability of exchange between leaf and environment. The nitrogen leaching from canopy decreased with the increase of plant nutrition, and this problemm should be further discussed and researched.