From nitrogen and calcium supply to field performance: a long-term study on sustainable nutrient management in citrus production

Abstract

Abstract Background and aims Sustainable citrus production requires nitrogen (N) management strategies that account for soil–plant nutrient interactions, particularly those affecting calcium (Ca) nutrition. In fertigated citrus orchards, strategies differing in NO₃⁻:NH₄⁺ balance and associated Ca supply affect soil chemical properties, plant nutritional status, fruit yield, and NUE. This study evaluated the effects of contrasting fertigation strategies, with or without foliar Ca application in a sweet-orange orchard. Methods A split-plot field experiment was conducted from 2020–23. Subplots received 220 kg N ha⁻ 1 yr⁻ 1 as calcium nitrate (CN; 100:0 NO₃⁻:NH₄⁺), nitrate-dominant mixture of calcium nitrate and ammonium nitrate (CN + AN; 75:25 NO₃⁻:NH₄⁺), or ammonium nitrate (AN; 50:50 NO₃⁻:NH₄⁺). Main plots received or not foliar Ca. Soil chemical properties, leaf nutrient status, fruit yield, and NUE were evaluated. Results CN and CN + AN were associated with higher soil pH and Ca availability, as well as approximately 15% higher leaf Ca concentration compared to AN. Responses were accompanied by higher fruit yield and NUE, with CN and CN + AN producing about 10 t ha⁻ 1 more fruit than AN across four harvests. Fruit yield was positively correlated with both leaf Ca concentration and leaf Ca:N ratio. Foliar Ca application did not improve leaf Ca concentration or fruit yield, and its association with lower NUE reflected the additional N supplied via Ca(NO₃)₂ without a corresponding increase in yield. Conclusion Fertigation differing in NO₃⁻:NH₄⁺ balance and Ca supply influenced soil chemical properties, plant nutritional status, fruit yield, and NUE. CN + AN was the best fertigation practice, whereas foliar Ca application provided no additional benefit to trees.