Abstract
Deficiencies of boron and zinc occur in coffee plantations despite the many fertilizer sources offered by the industry for the agriculture. Sparingly soluble fertilizers (SSF) have been used in several countries for many years. However, their effectiveness when applied to leaves is highly contested, and information about their use efficiency is still lacking. Experiments were set up to characterize the SSF of B and Zn according to particle size of fertilizers, and the spreading and retention of the particles in the leaf, comparing SSF (calcium borate, Zn oxide, and Zn borate) with soluble sources (boric acid and Zn sulfate) in four doses (mg.L-1): Experiment I (B 0, 130, 260, and 520), Experiment II (Zn 0, 200, 600, and 1,800), and experiment III (B 0, 43, 129, and 387, and Zn 0, 200, 600, and 1,800), to supply B and Zn for coffee plants. Microparticles of the SSF were found adhered to coffee leaves, and the Zn oxide was the one with the smallest particle size. SSFs were effective at increasing the Zn and B leaf concentrations in coffee. Dry matter of coffee increased 15% with applications of 270 mg.L-1 of B as calcium borate and 384 mg.L-1 of B as boric acid. Foliar application of Zn oxide at the dose of 1,800 mg.L-1 of Zn increased the leaf areas of the plants. High doses of Zn sulfate caused toxicity to coffee plants due to high saline concentrations. The microparticles found retained on the surface of the coffee leaves increased leaf concentration of B and Zn, which explained variations in the dry matter measurements and show the potential of the SSF for the development of fertilizers to improve the availability of micronutrients to coffee.
Highlights
There is a large supply of micronutrient fertilizers manufactured in the world, even though nutritional disorders associated with micronutrient fertilization remain problematic for many crops of agronomic interest (Bell and Dell 2008)
Microparticles of the Sparingly soluble fertilizers (SSF) were found adhered to coffee leaves, and the Zn oxide was the one with the smallest particle size
The concentration of Zn in the leaves with the highest dose of Zn oxide was 230 mg.kg-1, whereas with the same concentration in a foliar application when using the Zn borate source the leaf concentration was 178 mg.kg-1 (Fig. 2). This supports the need of small particles in the suspension fertilizer for the greater efficiency of the SSF in the supply of nutrients for the plants, since the increase of the contact surface facilitates the solubilization of the microparticles and gradually provides the micronutrient to the leaves (Wang and Nguyen 2018; Rossi et al 2019)
Summary
There is a large supply of micronutrient fertilizers manufactured in the world, even though nutritional disorders associated with micronutrient fertilization remain problematic for many crops of agronomic interest (Bell and Dell 2008). The sources most used for foliar applications in coffee are highly soluble, such as sulfates, chlorides, and nitrates. These fertilizer sources still offer challenges regarding application technology, such as the limited amount to be applied in the leaves to avoid phytotoxicity due to high saline indices (Kah et al 2018), the interaction that may occur with other products in the spray tank mix (Fernández et al 2013), and the necessity to perform new applications with each new shoot, since these micronutrients have low mobility in the phloem (Lacerda et al 2018; Leite et al 2007)
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