Abstract
The objectives of this study were: to evaluate the leaching potential of B in a Latossolo Vermelho-Amarelo (Oxisol) as a function of sources and doses of this micronutrient; among the sources tested (boric acid, ulexite and the commercial source H2 Boro), to determine the one with the lowest leaching potential; to evaluate leaching losses at different doses in each soil layer evaluated; and to identify chemical and physical variables of soils that influence B leaching. For that, two experiments were conducted in a greenhouse. The first one tested B leaching in the soil, with the three sources under study and five doses of B (0; 12; 24; 36; and 48 kg ha-1), whereas the second experiment evaluated the influence of soil physical and chemical attributes on B leaching using soils randomly collected in 22 localities in southeastern Goiás, Brazil. Regardless of the dose applied, ulexite led to the lowest soluble B content in the profile of the analyzed soils and also in the leachate. Boric acid was the only source that showed a different behavior in relation to B content in the different soil layers and in the leachate. In the soil layer from 21 to 30 cm, ulexite is the source with the lowest soluble B content. The behaviors of the more soluble sources, in this case boric acid and H2 Boro (H2 Agrosciences - Monoethanolamine borate), regardless of the dose, are very similar, being highly leachable in the profile of the Oxisol used. Soils with clayey texture and higher values of H+Al and CEC were able to retain higher B contents in the upper portion their profiles (layers from 0 to 10 cm and 11 to 20 cm), but soils with sandy texture and higher values of sum of bases showed greater B losses by leaching.
Highlights
Knowledge on boron (B) dynamics in soil is important for both correcting a possible deficiency of this micronutrient and preventing toxicity cases, since the leaching and adsorption of this element are important components for defining a balanced fertilization, at the correct time and using the best source
A significant difference was observed (H = 12.43; p = 0.006) in the soluble B content in the soil layers and in the leachate for the boric acid source, and the B content retained in the soil layer from 0 to 10 cm was higher than the B content leached (Figure 2)
Regardless of the B dose applied (12, 24, 36 and 48 kg of B ha-1), when the data are evaluated without being separated by segments, ulexite led to the lowest soluble B content compared to the other sources (p < 0.05), and boric acid and H2 Boro were similar (p > 0.05) at all doses applied (Figure 3)
Summary
Knowledge on boron (B) dynamics in soil is important for both correcting a possible deficiency of this micronutrient and preventing toxicity cases, since the leaching and adsorption of this element are important components for defining a balanced fertilization, at the correct time and using the best source. Absorption is dependent on the concentration in the soil solution and on the reactions between the micronutrient and the adsorbents in the soil, such as iron and aluminum oxides, clay minerals, organic matter and calcium carbonate, which are directly linked to soil texture, pH, liming and leaching, which are variables that influence soil B dynamics. The performance of B fertilization is directly related to the rapid leaching to deeper soil layers (Saltali et al, 2005; Communar and Keren, 2007; Favaretto et al, 2007; Oliveira Neto et al, 2009), mainly due to the high mobility of this nutrient in the soil solution. The high availability of the applied B, combined with the narrow range between deficiency and toxicity in plants, can lead to toxicity (Communar and Keren, 2007; Lima et al, 2007)
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