Effects of water regulation and biochar on soil and leaf nutrients of citrus

To reveal the effects of biochar application on soil and leaf nutrients in the root zone of citrus under different water management modes, 20-year-old Zigui navel orange was taken as the test object, and field experiments were carried out at the citrus orchard experimental station in Zigui County of Hubei Province for two consecutive years from 2019 to 2020. Effects of five biochar（B0: 0; B1: 4%; B2: 8%; B3: 12%; B4: 16%） application rates on nitrogen, phosphorus, and potassium contents in soil and leaves of citrus root zone under three water management conditions（W1: rain fed model; W2: fruit enlargement period 3 L/week, color conversion period 1 L/week; W3: fruit enlargement period 9 L/week, color conversion period 3 L/week） were studied. The results show that the contents of soil ammonium nitrogen, available phosphorus, and available potassium under the three water management conditions increase with the increase of biochar application rate, but the improvement of biochar on soil fertility is limited, and its growth trend gradually stabilizes with the increase of biochar application rate. The nitrogen content in citrus leaves decreases with the increase of biochar application rate, and the phosphorus and potassium contents in leaves show the same law, but the decreasing trend does not follow a linear relationship and affect the normal growth of crops. Under the treatments of 12% and 16% biochar application rates, the lower limits of nitrogen, phosphorus, and potassium in leaves tend to be stabilize, indicating that biochar enhances the nutrient absorption efficiency of citrus, resulting in nutrient dilution in leaves.