[Optimized nutrients management improved citrus yield and fruit quality in China: A meta-analysis]

Clarifying current situation of farmers' fertilization and yield in citrus producing areas and the effects of different fertilization measures can provide a scientific basis for improving the yield and quality of citrus in China. We retrieved 92 literatures on citrus fertilization from the CNKI and Web of Science to examine the impacts of nitrogen (N), phosphorus (P or P₂O₅), and potassium (K or K₂O) fertilizer dosage and partial productivity under farmers' conventional fertilization and experts' optimized fertilization, as well as the effects of optimized fertilization measures on citrus yield and quality by using meta-analysis approach. The average conventional application rates of N, P₂O₅, and K₂O were 507.3, 262.2, and 369.3 kg·hm^-2 in citrus production in China. Compared with conventional fertilization, optimized fertilization resulted in a reduction of N and P₂O₅ by 14.7% and 8.3%, an increase in K₂O application by 6.6%, which promoted partial productivity of N, P₂O₅, and K₂O fertilizers by 7.8%, 18.4%, and 14.7%, correspondingly. The optimized fertilization resulted in 11.9% and 2.8% increase in fruit yield and single fruit weight, while improved vitamin C content (Vc, 3.1%), total soluble solids (TSS, 5.9%) and total sugar content (TSC, 8.6%). Additionally, it also led to a reduction in titratable acid (TA, -3.4%) and total acid content (TAC, -3.6%), and consequently elevated the TSS/TA (14.0%) and TSC/TAC (9.5%). Among different optimized fertilization methods, the effect of optimized NPK + medium and/or micro element fertilizer on citrus yield and fruit quality was the best, especially NPK decrement ≤25% between optimized NPK measures. The effect of conventional NPK + organic fertilizer was higher than conventional NPK + medium and/or micro element fertilizer. However, different citrus varieties, including mandarins, pomelos, and oranges, showed different responses to optimized fertilization. Optimized fertilization management could synergistically improve citrus yield, fertilizer use efficiency, and fruit quality. Therefore, the strategy of integrated nutrient management1 with reducing NPK fertilizer, balancing medium and/or micro nutrient fertilizer and improving soil fertility by organic fertilizer should be adopted according to local conditions in citrus producing areas of China.