Chemical fertilizer has been excessively used for high yield of citrus around the world, especially in China; meanwhile, it deteriorates the citrus orchard soil environment. To resolve the conflict, the use of organic fertilizer provides a promising solution. However, the data about organic fertilizer used in citrus orchard is rarely available. Here, four treatments including CK (no fertilizer), CF (chemical fertilizer), OF + CF (chemical fertilizer reduction combined with organic fertilizer; application of N, P₂O₅, K₂O fertilizer and organic fertilizer is 0.564, 0.236, 0.336 and 10 kg/plant), and BF + CF (chemical fertilizer reduction combined with bioorganic fertilizer; application of N, P₂O₅, K₂O fertilizer and bioorganic fertilizer is 0.508, 0.320, 0.310 and 10 kg/plant) were performed in a ‘Ponkan’ (Citrus reticulata Blanco) orchard to evaluate the effect of organic fertilizer on citrus yield, growth, soil properties etc. when nutrients of fertilizer of each treatment were equal except CK. The data obtained in 2019 and 2020 showed that both OF + CF and BF + CF were beneficial to improve soil fertility (soil physicochemical and microbe properties) and citrus growth physiology (growth, nutrient and photosynthesis), alleviate NO₃⁻-N leaching, and promote yields. Comprehensive evaluation indicated that BF + CF was more effective than OF + CF. Together, organic fertilizer has the potential to substitute partial chemical fertilizer with improvement in soil properties, growth physiology, and yield of citrus.

In this study, we investigated the effects of the combined application of different doses of potassium and organic fertilizers on the nutrient uptake, yield, and quality of Newhall navel oranges (Citrus sinensis Osb. cv.). The citrus trees were treated with potassium fertilizer alone or with one of three combinations of organic and potassium fertilizers. Spring shoots, autumn shoots, and fruit were collected when they reached maturity, and the relevant indexes were determined by conventional methods. The soil carbon flux was measured 15, 35, 65, and 95 days after fertilizer application by a soil gas flux measuring instrument. The results showed that the dry weights of leaves and twigs of the spring shoots were 43.1% and 99.8% higher in the OM15+K05-treated (15 kg organic manure and 1.05 kg potassium sulfate per plant) than in the OM0+K25-treated (1.25 kg potassium sulfate per plant) plants, respectively. Combined potassium and organic fertilizer application helped the shoots and fruits to absorb more mineral nutrients. As a result, the fruit yield increased, fruit surface color improved, and skin thickness became thinner. The internal quality of the fruit was also improved by the combination of different potassium fertilizers and organic fertilizers. The fruit quality was optimal for the OM10+K15-treated plants. The recommended doses of organic and potassium sulfate fertilizers for Newhall navel orange orchards with purple paddy soil in southwestern China are 5–10 kg/plant and 1.15–1.20 kg/plant, respectively.