Abstract
Nitrogen and micronutrients have a key role in many citrus plant enzyme reactions. Although enough micronutrients may be present in the soil, deficiency can develop due to soil depletion or the formation of insoluble compounds. The objectives of this study were to (1) determine the adsorption, distribution, and availability of Zn in a sandy soil; (2) compare the effectiveness of foliar and soil application methods of Zn on Huanglongbing [HLB] affected trees; (3) compare foliar application rates of Zn for HLB-affected trees; (4) determine the effect of N rates on yield, soil inorganic N distribution patterns, and tree growth parameters. Tree rows were supplied with three N rates of 168, 224 and 280 kg·N·ha−1 and Zn at single and double recommended rates (recommended rate = 5.6 kg·Zn·ha−1) using foliar and soil application methods, in a split-plot experimental design. The results show that Zn concentration in the 0–15 cm soil depth was three times higher than the 30–45 and 45–60 cm soil depths during the study. An adsorption study revealed high Zn (KD = 6.5) sorption coefficients at 0–15 cm soil depth, while 30–45 and 45–60 cm depths showed little sorption. Leaf Zn concentration for foliar spray was two times higher than the soil application method. A nitrogen level of 224 kg N ha−1 improved canopy volume when compared to other N levels at the expense of reduced fruit weight. Foliar Zn application at 5.6 or 11.2 kg ha−1 and N rate at 224 kg ha−1 appear to be adequate for improving the performance of HLB-affected citrus trees.
Highlights
Several cultivars of sweet orange cultivated in Florida are reported to have a significant yield response to N fertilizers at 168 kg ha−1 [1]
A previous study claimed enhanced knowledge of the N budgets for citrus groves, which resulted in the development of appropriate best management practices (BMPs) to maintain production while protecting the environment [3]
Canopy volume was improved when 224 kg N ha−1 was applied compared to other levels of Canopy volume was improved when 224 kg N ha−1 was applied compared to other levels of nitrogen
Summary
Several cultivars of sweet orange cultivated in Florida are reported to have a significant yield response to N fertilizers at 168 kg ha−1 [1]. Nitrogen management programs showed that the ideal N rate for increased fruit yield and quality is approximately 260 kg N ha−1 yr−1 under best management practices (BMPs) and a proper irrigation schedule [2]. BMPs are designed to decrease N leaching into groundwater by applying fertilizers in splits with appropriate rate and fertigation with improved irrigation scheduling [2,3,4]. The relationship between mineral nutrients and plant disease eventually influences the intensity of disease symptoms [8]. Citrus micronutrient (especially Zn) deficiencies have been observed in shallow soils with a high water table, in extremely sandy areas, and in calcareous soils [12]. Soil and foliar application of micronutrients has been recommended to correct deficiencies in Florida citrus [13]
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