Soybean is one of the annual crops most demanding of boron (B); however, borate fertilizer should be managed cautiously, especially in regard to application rates, because of the narrow range between the appropriate level and toxic level for this nutrient in the soil. Another important factor directly related to B availability to plants refers to soil water conditions. In this context, this study evaluated the effect of sources and application rates of B on soybean growth (Glycine max) in a Latossolo Vermelho (Oxisol) with a sandy texture, subjected to different water tensions. The experiment was conducted in greenhouse in pots with 5 dm³ of soil. We used a split plot experimental design in a 5 x 2 x 3 factorial arrangement with five application rates of B (0.0, 0.25, 0.5, 1.0 and 2.0 mg dm-3), two B sources (boric acid and colemanite) and three soil water tensions (0.01, 0.03 and 0.10 MPa), with four replications. The results indicated that soybean growth is not affected when the level of soil water tension is maintained up to -0.1 MPa. Root system growth was adversely affected by B application rates of up to 2 mg dm-3 in soil with an initial level of 0.32 mg dm-3. The levels of B in the soil and in leaf tissue of soybean increase linearly with nutrient application rates in the soil, and typical symptoms of B toxicity in soybean leaves were observed at the highest rate (2 mg dm-3 of B).
Glycine max; micronutrient; water tension
