The adequate dose of Mo required for soybean seed treatment is low when associated with Cu, Mn, and Zn compared to its association with Co and Ni, although increasing the risk of toxicity

Abstract

The seed treatment with Mo associated with other elements, such as Ni and Co, and with micronutrients, such as Cu, Mn, and Zn, has been highlighted. The use of these associations can affect the adequate dose of Mo and the risk of toxicity. This study aimed to determine whether the optimal and the toxic dose of Mo can be affected by the accompanying elements of the group Co and Ni in relation to Cu, Mn, and Zn for the treatment of soybean seeds. Two experiments were carried out. The treatments in experiment I consisted of five doses of a product containing Mo, Co, and Ni at the concentrations of 0, 30-, 60-, 90-, and 120-mL ha−1. In experiment II, the treatments consisted of five doses of a product containing Mo, Cu, Mn, and Zn at the concentrations of 0, 50-, 100-, 200-, and 400-mL ha−1. The optimal dose of Mo was low (6.7 g ha−1) when applied along with Cu, Mn, and Zn as accompanying elements in relation to Co and Ni (17.5 g ha−1 of Mo). Application of the optimal dose provided an increase in N accumulation and in the chlorophylls, carotenoids, and phenolic compounds, decreasing the extravasation of electrolytes and increasing photosynthetic efficiency, dry matter, and yield. Mo toxicity was more severe with Cu, Mn, and Zn as accompanying elements, already occurring at the low dose of 18.9 g ha−1 Mo, which is much lower when Mo is associated with Co and Ni (32 g ha−1 Mo).