Chitin combined with selenium reduced nitrogen loss in soil and improved nitrogen uptake efficiency in Guanxi pomelo orchard

Nitrogen cycling in soil, which associated with microbes, plays an important role in plant growth. Irrational application of nitrogen fertilizer could disrupt the structure of soil microbial community, thus inhibiting the uptake of nitrogen by plants and increasing nitrogen leaching in soil. Field and pot leaching experiments with the combined application of chitin fertilizer and selenium (Se) were carried out in order to develop an approach to improve the efficiency of nitrogen fertilizer utilization and reduce runoff by nitrogen loss in orchards of Guanxi pomelo in Fujian Province. Our results showed that application of chitin fertilizer combined with Se to the soil with reduced nitrogen and phosphate fertilizer (nitrogen fertilizer decreased by 25% and phosphate fertilizer decreased by 50%) could significantly increase the fruit yield, vitamin C and solid-acid ratio in the fruit. The application of chitin fertilizer and Se can not only lead to the increase of total nitrogen content in plant leaves but also the alkali-hydrolyzable nitrogen content in soil which enhancing soil nitrogen supplying capacity. It has been found that the adding the chitin fertilizer and Se into soil can significantly affect the structure and functional categories microbial communities and its activities. This is directly evidenced by the findings that the expression level of several groups of N metabolism and transporting related genes (i.e. amoAB and nxrA in nitrification, narG, nirK, norBC, and nosZ in denitrification, nirD, narH in dissimilatory nitrogen reduction, and ureC in ammoniation) has been drastically up-regulated. Our results indicate this strategy for reducing N and P input while maintaining and improving plant performance by supplementing with micronutrient Se and chitin fertilizer can increase the fruit yield and improve the quality of Guanxi pomelo through improving fertilizer use efficiency.