Optimized fertilization and fruit load regulate yield, quality, and nutrient uptake in pomelo trees

Mineral nutrients play a crucial role in ensuring consistent yields of citrus trees; however, the effects of fertilization management and fruit load level on yield and nutrient uptake in pomelo trees remain unclear. A two-year field experiment was conducted on a 15-year-old ‘Guanximiyou’ pomelo [ Citrus grandis (L.) Osbeck] orchard, involving two fertilization practices (farmer’s practice: 1 000 N-900 P 2 O 5 -900 K 2 O; optimized practice: 250 N-100 P 2 O 5 -200 K 2 O plus 2 000 kg · ha -1 organic fertilizer) and three fruit load levels (low, medium, and high fruit loads: 40 ± 5, 65 ± 5, and 90 ± 5 fruits per plant, respectively). Pomelo yield, fruit quality (TSS, TA, VC, TSS/TA, juice pH, soluble sugar), tree biomass (pruned litter and aboveground apparent biomass), and nutrient uptake were investigated. The results revealed that, compared with the farmer’s practices, optimized fertilization practices-maintained fruit yield and quality while significantly reducing NPK fertilizer inputs. Fruit yield was higher, but fruit quality was lower in the high fruit load treatment than in the low and medium fruit load treatments. There were no differences in the apparent aboveground biomass between the optimized and farmer’s practices, but a high fruit load significantly decreased the pruned litter biomass. In general, optimized fertilization did not affect nutrient uptake in pomelo trees, and the accumulation of C, N, P, K, Ca, and Mg in the fruit increased, whereas the accumulation in the leaf and branch organs decreased with increasing fruit load, resulting in a shift in nutrient distribution between organs. Furthermore, the nutrient balance results revealed that farmer’s practice resulted in an excessive surplus of N, P, and K, with certain deficiencies in Ca and Mg across all fruit load levels, whereas optimized fertilization helped balance the nutrient demand in pomelo trees and reduce the nutrient surplus in pomelo orchards. Moreover, optimized fertilization coupled with a low fruit load improved system C storage in the pomelo orchard. In conclusion, optimized fertilization coupled with an appropriate fruit load can maintain comparable yield and quality, while reducing nutrient surplus and improving carbon storage, achieving a balance between vegetative and reproductive growth, and thereby promoting the sustainable development of pomelo orchards.