Water-nitrogen Coupling Effects On Growth And Water Use Efficiency Of Jatropha Curcas

Jatropha curcas as a very important energy plant with high oil content seeds has drawn wide attention from worldwide experts and scholars. Jatropha curcas has an even more rapid development in Yunnan province which located in southwest of China, the planting area in planning alone is more than one million hectares now, and mostly are artificial pure forests. Many years practice have shown that, the most important issue restraining Jatropha curcas’ healthy growth and production increment is the severe dislocation of rain and key period of water demand, which leads an extremely low utilization of water and fertilizer resource. According to the climate and soil characteristics in Yunnan, in addition to cultivation of seeds, the impact of the amount of water and fertilizer to increase the yield of Jatropha curcas is the most important part.As one of the research contents in the National Natural Science Foundation of China51009073(Limited irrigation and nitrogen fertilizer on Yield and quality effect of Jatropha curcas), this thesis has studied water-nitrogen coupling effects on growth and water use efficiency of Jatropha curcas. Water and nitrogen controlling experiments were conducted in pots to plant Jatropha curcas with high, medium and low irrigation, and high, medium and none nitrogen amount. Plant gorwth parameters such as height, stem diameter, leaf area, root-shoot ratio, total dry mass etc., and soil physical parameters such as water use efficiency (WUE), evapotranspiration etc., were measured, the effects on growth and WUE of different irrigation thresholds and nitrogen were also quantitatively detected. Based on the statistical processing of the experiments data, the effects of water-nitrogen coupling, different irrigation thresholds and nitrogen on growth and WUE of Jatropha curcas were analyzed. The results showed that:1) In two trials, the Jatropha curcas can survive with different severing water stress treatments (15.3mm and30%field capacity) in the irrigation cycle7and10days, showing a strong anti-drought ability;2) In irrigation and nitrogen fertilizer coupling test, the effects of different irrigation and nitrogen in Jatropha plant height, stem diameter variation, leaf area, root-shoot ratio, the impact of irrigation water use efficiency reached a significant level. As the amount of irrigation water increased, the height, stem diameter, leaf area and total dry mass of Jatropha significantly increased respectively, and root-shoot ratio of medium irrigation treatment reached the maximum. Nitrogen treatments principally affected the height and leaf area, and stem diameter and root-shoot ratio decreased with the increasing nitrogen amount.3) In water irrigation and nitrogen fertilizer coupling test, compared to high irrigation and high nitrogen treatment, medium irrigation and medium nitrogen treatment means decreased plant height, stem diameter and total dry mass by11.65%,21.32%and12.38%, respectively, but the root-shoot ratio and leaf area significantly increased by47.82%and16.28%under saved irrigation water and nitrogen fertilizer by37.5%and50%, respectively, and after irrigating, the transpiration significantly reduced by20.54%,15.34%and11.80%at2days,3days and4days respectively, which led to the irrigation water use efficiency(WUEi) of Jatropha curcas significantly increased by40.25%.4) Through the irrigation thresholds and nitrogen fertilizer coupling experiment, we find that, in addition to the nitrogen application rate on leaf area had no significant effects, irrigation thresholds, nitrogen fertilization and the irrigation thresholds and nitrogen fertilization interaction of Jatropha have significant effects on root-shoot ratio and total dry mass, and only irrigation thresholds have significant effects on WUEi.Conclusion:In order to save irrigation and nitrogen amount, in the water irrigation and nitrogen fertilizer coupling test, the best combination in favor of growth of Jatropha curcas is medium irrigation and medium nitrogen treatment(25.5mm,0.3g); In the irrigation thresholds and nitrogen fertilizer coupling experiment, the best combination in favor of growth of Jatropha curcas is medium irrigation and medium nitrogen treatment(50%field capacity,0.4g).