Evaluation of extraction procedures on determination of critical soil and foliar levels of boron and zinc in coffee plants
1998
Lima Filho, O.F de | Malavolta, E.
Six-month-old coffee plants were grown in the greenhouse in pots containing a Dark Red Latosol (Orthox), to study the effect of boron (B) and zinc (Zn) on growth and leaf content of these micronutrients. Boron was added at levels of 0, 1, 3, and 5 mg kg-1, whereas Zn was added in proportions of 0, 5, 10, and 20 mg kg-1. Boron application affected total dry matter, height and diameter of stem, length and number of plagiotropic branches, number of leaves, ratio between total leaf area and number of leaves (ULA), ratio between total leaf area and total dry matter (LAR), leaf moisture, and index of potential yield (IPY). The IPY, defined as the ratio of dry matter of developed flowering buds plus flowers to the dry matter of underdeveloped flower buds and flowers, proved to be the an excellent parameter to assess B levels. Leaf B, well correlated with IPY, varied from 50 to 60 mg kg-1. Available B in soils, in mg kg-1, ranged from (with the critical levels between parentheses): 0.2 to 0.3 (0.2), as determined in a saturation paste, 0.6 to 1.0 (0.9), as determined in a hot water extract, 0.9 to 1.3 (1.2), with monocalcium phosphate in acetic acid, 1.1 to 1.4 (1.3), by Mehlich 1 method, 2.1 to 2.4 (2.4) by 0.05N HCl, 2.2 to 2.4 (2.4), by 0.1N HCl. Zinc additions caused a decrease in growth when B supply was limiting. On the other hand, B had no effect on dry matter yield when Zn was not added. Adequate Zn soil levels in mg kg-1 were 4.4, as determined by 0.05N HCl extraction, 4.2, by 0.1N HCl, 3.9, by Mehlich 1, 2.7, by EDTA extraction, and 2.1, in DTPA extracts. Leaf Zn, not affected by Zn additions, was between 12-14 mg kg-1.
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