The effect of nitrogen and phosphorus fertilizer reduction on yield and quality of Guanxi pomelo

Objectives In view of excess fertilization in Guanxi pomelo in Pinghe County, Fujian Province, reduction of nitrogen and phosphorus application was studied for higher yield and better quality fruit.

Methods The field experiment was conducted with white pulp Guanxi pomelo trees. Based on previous questionnaire, the maximum amount of nitrogen and phosphorus fertilization was set up: N 1.60 kg/(plant·a) (N1), P₂O₅ 1.30 kg/(plant·a) (P1), with 30% gradient reducing of nitrogen fertilization and 35% gradient reducing of phosphate fertilization respectively. Nine treatments were designed as N1P1, N1P2, N1P3, N2P1, N2P2, N2P3, N3P1, N3P2, N3P3 and N3P3. The nitrogen, phosphorus and potash fertilizers were orderly applied at flowering (mid-March), steady fruiting (mid-May), filling fruiting (late July or early August) and wintering periods (late November). Calcium and magnesium fertilizers were used in the middle of March, and the furrow was dripped applied along the tree canopy.

Results Reducing nitrogen and phosphorus fertilization did not significantly decrease, but increased the fruit yields to some extent, and the increment by reducing nitrogen was better than that by reducing phosphorus did. Reducing nitrogen and phosphorus fertilizer improved fruit edible rate, total soluble solids, solid acid ratio and Vitamin C contents, but decreased the fruit aspect ratio, peel thickness and titration acid content. The fruit edible rate, total soluble solids and Vitamin C contents in N2 were significantly higher than in N1, the fruit aspect ratio and Vitamin C content in P2 were significantly lower than in P1, the edible rate in P3 was significantly higher than P1. Among the treatments, N2P2 performed the best. The interaction between reducing nitrogen and phosphorus extremely significantly affected the fruit and soluble solids, and significantly affected the thickness of pericarp, juice yield, edible rate and vitamin C content. The results of principal component analysis and cluster analysis also showed that the fruit quality of N2P2 treatment was the better than the other treatments, with the highest score of 2.20 and higher167.06% than the second.

Conclusions Under the current nitrogen and phosphorus fertilizer input levels, reducing nitrogen and phosphorus fertilizer inputs to some extent will not decline but raise the fruit yield and improve the quality of Guanxi pomelo fruit remarkably. For the experimental condition, nitrogen and phosphorus fertilizer could be reduced by 30% and 35% respectively from currently quantities, which are 1.12 kg N per plant per year and 0.85 kg P₂O₅ per plant per year as optimum option.