Nutritional status of different citrus trees and the recommended dosages of N, P and K for citrus production in China

Objectives Mineral nutrient contents in citrus fruits, as well as the fertility status of citrus orchard soils were investigated across China, specific fertilizer rates of nitrogen, phosphorous and potassium were proposed for each type of citrus in China.

Methods The main species of citrus in China included mandarin, sweet orange, pomelo, lemon and hetero-citrus. The citrus production belt was spread across 11 provinces and were divided into 1200 sampling units, based on the soil type and orchard age; each sampling unit was 3.3–6.7 hm². From 2010 to 2017, soil and leaf samples were collected for nutrient content analysis. The fertilizer dosage and fruit yields were investigated at the same time.

Results The recommended amounts of N, P, and K fertilizers (N, P₂O₅, K₂O, kg/hm² respectively) for low-fertility orchards were: mandarin orange 189.75–253.00, 76.20–93.13 and 133.20–159.84; sweet orange 176.94–235.92, 101.02–123.47 and 128.03–153.64; pomelo 134.76–179.68, 69.04–84.38, 125.21–150.25; lemon 91.33–121.77, 55.43–67.75 and 79.68–95.62; hetero-citrus 109.42–145.89, 70.06–85.63 and 93.18–111.81. The recommended amounts of N, P, and K fertilizers (N, P₂O₅, K₂O, kg/hm² respectively) in the medium-fertility orchard were: mandarin orange 216.86–337.33, 83.82–139.70 and 145.31–245.91; sweet orange 202.22–314.56, 111.12–185.20 and 139.67–236.37; pomelo 154.01–239.57, 75.95–126.58 and 136.59–231.15; lemon 104.37–162.36, 60.98–101.63 and 86.92–147.10; hetero-citrus 125.05–194.52, 77.07–128.45 and 101.65–172.02. The recommended dosages of N, P, and K fertilizers (N, P₂O₅, K₂O, kg/hm² respectively) for high-fertility orchards were: mandarin orange 303.60–474.38, 118.06–190.50 and 222.00–330.00; sweet orange 283.10–442.35, 156.51–252.55 and 213.39–320.08; pomelo 215.62–336.90, 106.96–172.60 and 208.68–313.01; lemons 146.12–243.54, 85.88–147.82 and 132.80–212.48; hetero-citrus 175.07–273.54, 108.55–175.16 and 155.29–232.94.

Conclusions Among the 5 citrus species, mandarin orange requires the highest N and K fertilizers and sweet orange requires the highest P fertilizer. The N∶P₂O₅∶K₂O ratio is 1∶0.37–0.41∶0.63–0.73 for mandarin orange, 1∶0.52–0.59∶0.65–0.75 for sweet orange, 1∶0.47–0.53∶0.84–0.97 for pomelo, 1∶ 0.56–0.63∶0.79–0.91 for lemon, and 1∶0.59–0.66∶0.77–0.89 for hetero-citrus.