Micronutrients status of Florida soils under citrus production

Abstract

Micronutrient nutrition plays an important role in citrus production. Soil extraction techniques to measure the status of bio‐available micronutrients are extremely valuable in the diagnosis of deficient or toxic levels of micronutrients. Mehlich 3 (M3), Mehlich 1 (M1), ammonium bicarbonate‐DTPA (ABDTPA), and ammonium acetate, pH 7.0 (AA), extractants were evaluated for their ability to extract Cu, Fe, Mn, and Zn using 45 citrus grove soils, representing 20 soil series with widely varying physical and chemical characteristics and production practices. The mean concentrations of M3 extractable Fe, Mn, Cu, and Zn were 5.5‐, 2.2‐, 1.6‐, and 1.2‐fold greater, respectively, than those extracted by M1. ABDTPA was more efficient in the extraction of Fe, Cu, and Zn, as compared to the M1 extradant, by 3.3‐, 3.0‐, and 1.4‐fold, respectively. Among the four extractants, AA was extremely inefficient in extraction of all the four micronutrients. Evaluation of the data from all 45 citrus grove soils revealed significant pH effects on extractable Zn by M3, Ml, and ABDTPA extractants and Fe by M1 and ABDTPA extracts only. However, evaluation of the data from pH x Cu experiment on a Candler fine sand (0–15 cm depth soil; pH ranging from 4.5–6.9) showed a negative relationship between the Fe extracted by M3, Ml, and ABDTPA extradants and soil pH. Both extractable Mn and Zn were positively correlated to soil pH except for Mn extractable by ABDTPA. Good correlations (r² > 0.52) were observed between M3 vs. Ml extractable Cu, Fe, Mn, and Zn and M3 vs. ABDTPA extractable Cu and Zn. Good correlations were generally found between M3 and AA extractable Cu, Mn, and Zn. However, poor extractability of all micronutrients by AA indicated that it is not a suitable extractant for micronutrient analysis of the soil studied. The results suggest that M3 is a suitable extractant for micronutrient analysis on sandy soils under Florida citrus production.