Aplicação foliar de níquel na cultura da soja sob condições do Cerrado

Abstract

Soybeans are a commodity of great economic value in Brazil, especially productive in the Central-West region. However, climate change is aggravating agricultural challenges, with droughts and high temperatures causing stress in plants. This leads to the excessive production of reactive oxygen species (ROS), impairing soybean development. As a response, foliar fertilization emerges as an alternative to mitigate these effects. Nickel (Ni), in turn, is essential to activate urease, an enzyme linked to nodulation and nitrogen metabolism in plants. Thus, the objective of the study was to evaluate the effect of foliar fertilization with nickel on productivity, protein accumulation in grains and its influence on the antioxidant system in soybeans. The experiment was conducted in the 2024/25 harvest, in an experimental area located in the Barreirinho crossing, in the municipality of Dourados, Mato Grosso do Sul, in a randomized block experimental design. The treatments consisted of foliar application of Ni doses (0, 20, 40, 60, 80 and 100 g ha-1 Ni, 50% V4 and 50% in R5) in four replicates. The cultivar used was Brasmax Garra IPRO. Sowing fertilization was performed using 350 kg ha-1 of the formula 02-18-15. Nickel sulfate was used as the nutrient source, which was applied at a volume of 150 L H2O ha-1. The number of pods per plant, number of grains per pod, weight of 1000 grains, productivity, crude protein content of the grains, in addition to the foliar determination of total proteins (PROT), superoxide dismutase (SOD) and peroxidase (POX) were evaluated. Nickel did not influence productivity, but contributed to the protection metabolism and quality of the grains, here represented by the protein content. The highest PROT and POX values are associated with the non-use of Ni, indicative of stress due to greater metabolic activity for defense. While the highest SOD value is associated with treatments using 20 to 60 g ha-1 of Ni. These values of the components of the antioxidant defense system demonstrate that the use of Ni is a precursor in the mitigation of abiotic stresses, as it is a micronutrient that improves N metabolism, contributing to the synthesis of proteins important for the formation of these antioxidant defensive components. The highest crude protein content is associated with the dose of 20 g ha-1 of Ni, which stimulated the activity of the urease enzyme and increased the amount of ureides available for the plant to use. Ni has been shown to be an important micronutrient for plants, as it influences the antioxidant defense system and gives the grains higher protein quality, being important for the food industry.