Objectives In Fujian Province, nitrogen and phosphorus fertilizers are used excessively in the production of Guanxi Pomelo, resulting in a substantial reduction in the fruit's taste and benefits. We studied the possibility of a continuous decrease in N and P fertilizer input.

Methods A 5-year localized field experiment was conducted in Pinghe, Fujian Province, from 2016 to 2021. The white pulp pomelo trees tested were 25-year-old originating from a grapefruit stock. The average N and P application rates were N 1.60 kg/plant (N3) and P₂O₅ 1.30 kg/plant (P3). Subsequently, the N treatment levels were decreased by 30% (N2) and 60% (N1), the P treatment levels by 35% (P2) and 70% (P1), giving seven treatments (N3P3, N2P3, N2P2, N2P1, N1P3, N1P2 and N1P1) in total. We counted the number of fruits per tree and weighed each individual fruit at maturity. In addition, the fruit samples were peeled to determine their weight and quality indices.

Results Compared with N3P3, N2 increased fruit yield in the first four years by 4.96%–47.58% but decreased in the fifth year by 6.31%. N1 increased the first-year fruit yield by 42.12% but decreased in the next three years by 2.36%–23.42%; P2 and P1 did not change across the five-year fruit yield. N2 (P<0.05) decreased the five-year fruit peel thickness by 6.42%–18.95%. In contrast, it increased the fruit soluble solid content by 5.36%–16.95%, the solid and acid ratio by 5.12%–24.10% in the first four years, and increased fruit vitamin C content by 2.18%–14.18% in the five years , respectively. P2 decreased single fruit weight and peel thickness by 0.52%–10.99% and 7.24%–15.14% in the five years, but increased fruit solid to acid ratio by 0.82%–22.21%in the first four years . The results of the principal component analysis and cluster analysis showed that the N3P3 recorded the lowest comprehensive score for fruit quality across the five years, while N2P2 had the highest comprehensive score in the first four years.

Conclusions Decreasing 30% of N application based on the local farmers’ practice could increase or stabilize fruit yield, decrease fruit peel thickness and enhance fruit taste for four years. A 35% and 70% decrease in P input did not affect fruit yield and qualities across the five-year study period. However, we recommend testing the appropriate N and P input in the long run for efficient Guanxi Pomelo production.