Micronutrientes na construção da fertilidade e morfofisiologia da soja no cerrado tocantinense

Abstract

With the expansion of agricultural activity in MATOPIBA, the construction of soil fertility in micronutrients, especially B, is important due to its role in plant production, being highly demanded by the soybean crop. Thus, it is necessary a precise and efficient management of borated fertilization, since the practice - considered of high cost, is influenced by factors related to the type of soil, the solubility of the sources, the mode of application and the genetic variety. The objective of this work was: 1. To evaluate the availability of B in the soil for the construction of the fertility of a Oxisol and Entisol. For this, treatments obtained in 5x10 factorial consisted of five sources (boric acid, sodium octaborate, sodium tetraborate, oxide and oxysulphate) and ten incubation times (0, 5, 10, 15, 25, 40, 55, 70, 85 and 100 days), with three replicates. The dose of B applied was 4.0 mg dm-3 in soil samples of 0.5 dm3 with pH corrected to 6.0; 2. To evaluate the effects of fertilization with H3BO3 in the soil and leaf on the development of soybean plants cv. M8808Ipro. For this, the treatments obtained in factorial 3x2 consisted of three doses of B in the soil: 0 (control); 0.62 and 3.4 kg ha-1, in the absence and presence of foliar supplementation, with four replications; 3. Evaluate the effects of fertilization with micronutrients in the form of oxides on nutrition and morphology of soybean plants cv. M8349Ipro. For this, treatments consisted of fertilization with micronutrients at the doses: 0.00 (control), 56.67 and 211.11 kg ha-1, corresponding to the interpretation of B classes in the soil: very low, ideal and high. The physiological parameters were quantified in the V6 and R2 stages of the culture. The availability of B in the soils was lower with the use of the more soluble sources and the efficiency of the fertilization with oxide and oxysulphate was superior to 80%. The uptake of B by plants increased gradually with the supply of H3BO3 via soil and foliar, while the physiological apparatus was more efficient in the absence of foliar supplementation. Fertilization with increasing doses of micronutrients in the form of oxides via soil influenced in different ways the absorption of B, Cu, Mn and Zn by plants, and reduced the yield of biomass and soybean grains. However, the dose 56.67 kg ha-1 conferred higher total chlorophyll in R2 and better stomatal conductance and internal carbon concentration in V6. Fertilization with more soluble borate sources is not efficient for the construction of soil fertility in B. Fertilization with H3BO3 in the soil and foliar does not improve morphophysiology and soybean production in clayey soils with an initial B content of 0.30 mg dm-3, although it increases leaf B accumulation. Fertilization with micronutrients in the form of oxides incorporated in the soil does not increase the yield of soybeans, despite the application of 56.67 kg ha-1 of the fertilizer to provide adequate B and Cu leaf contents and to improve the photosynthetic activity of the plants.