Effect of deficit irrigation and nitrogen fertilizer application on soil nitrate-nitrogen distribution in root-zone and water use of Jatropha curcas L.

The demand for energy has risen rapidly due to increasing industrialization and modernization of the world, and the majority of energy is derived from fossil sources such as petroleum, coal and natural gas. However, alternative fuels from renewable feedstock provide alternatives to fossil fuels to solve the problems of the limited reserves of fossil fuel. Jatropha curcas L. has recently drawn the attention due to its tremendous potential as a biodiesel crop. A pot-grown experiment was conducted to investigate the effect of deficit irrigation and nitrogen fertilizer application on soil water content, soil nitrate-nitrogen(NO-3-N) distribution in root-zone, and evapo-transpiration quantity, dry mass accumulation, base stem diameter-plant height ratio, root-shoot ratio, healthy index and water use of young Jatropha curcas L. trees. Four irrigation levels (W1: 100%ET (ET: Evapo-transpiration); W2: 80% W1; W3: 60% W1; W4: 40% W1) and three added nitrogen levels (N0: 0; N1: 0.4g N/kg; N2: 0.8g N/kg, respectively) were designed in the study. Results showed that the NO-3-N content in topsoil (0-5 cm) was less than that in 10 and 15 cm under W1, W2 and W3 treatment, respectively; the soil NO-3-N content of topsoil in 5 cm was higher than that in 10 and 15 cm under W4 treatment; the mean soil NO-3-N content under W2 treatment was lower than that under W1, W3 and W4 treatment. Compared to W1 treatment, W2 treatment significantly increased mean base stem diameter-plant height ratio and healthy index, and root, shoot and total dry mass of young Jatropha curcas L. trees, respectively. Meanwhile, W2 treatment significantly decreased mean evapotranspiration, and thus W2 treatment significantly increased irrigation water use efficiency and total water use efficiency of young Jatropha curcas L.trees. But W3 and W4 treatment significantly decreased mean irrigation water use efficiency and total water use efficiency of young Jatropha curcas L.trees. Compared to N0, N2 treatment significantly increased mean healthy index, and root, shoot and total dry mass, irrigation water use efficiency and total water use efficiency of young Jatropha curcas L.trees, respectively. And mean irrigation water use efficiency and total water use efficiency of N2 treatment was higher than N1 treatment, respectively. Compared to W1N2 treatment, W2N2 treatment saved irrigation water by 10.7%, and decreased soil water content, soil NO-3-N content and evapo-transpiration quantity by 22.8%, 12.1% and 9.6%, respectively. However，W2N2 significantly increased base stem diameter-plant height ratio and healthy index of seedlings by 24.7% and 27.6%, respectively. Meanwhile, compared to W1N2 treatment, W2N2 increased root, shoot and total dry mass accumulation by 22.3%, 18.3% and 19.2%, respectively, thus increased irrigation water use efficiency and total water use efficiency of young Jatropha curcas L.trees by 36.6% and 35.0%, respectively. This research suggested that W2N2 treatment not only saved irrigation water, and decreased evapo-transpiration quantity, but increased dry mass accumulation, base stem diameter-plant height ratio, root-shoot ratio, thus W2N2 treatment improved healthy index of seedlings and water use efficiency of young Jatropha curcas L. trees.