Aplicação foliar de sulfato de magnésio em estádios fenológicos sobre a produtividade, a nutrição e a qualidade bromatológica da aveia-preta

Abstract

Seasonality in forage production poses major challenges to livestock systems during autumn and winter, making black oat (Avena strigosa Schreb.) cultivation is an essential strategy for animal upplementation. To ensure forage conservation and a continuous supply of nutrients, hay production under irrigated systems has been adopted, shifting the agronomic focus from maximizing biomass yield to improving the bromatological quality of the forage. Since magnesium (Mg) acts as an essential enzymatic cofactor in carbohydrate loading and translocation, its supplementation may enhance the energy value of hay. Therefore, this study aimed to evaluate the effects of different foliar application timings of magnesium sulfate on the biometric, productive, nutritional, and bromatological characteristics of irrigated black oat. The experiment was conducted under field conditions at the Federal University of Grande Dourados (UFGD), Dourados, Mato Grosso do Sul, Brazil, using a randomized complete block design with seven treatments and four replications. The treatments consisted of foliar applications of magnesium sulfate at different phenological stages: T1 – control (without Mg); T2 – 3 kg ha⁻¹ magnesium sulfate at the three fully expanded leaf stage; T3 – 3 kg ha⁻¹ magnesium sulfate at tillering; T4 – 3 kg ha⁻¹ magnesium sulfate at stem elongation; and sequential applications: T5 – 3 kg ha⁻¹ at the threeleaf stage + 3 kg ha⁻¹ at tillering; T6 – 3 kg ha⁻¹ at the threeleaf stage + 3 kg ha⁻¹ at stem elongation; and T7 – 3 kg ha⁻¹ at tillering + 3 kg ha⁻¹ at stem elongation. SPAD index, plant height, fresh and dry biomass yield were evaluated. The concentrations of macro and micronutrients were determined in diagnostic leaves, and the bromatological composition was assessed through neutral detergent fiber (NDF), acid detergent fiber (ADF), lignin, crude protein (CP), and nonfibrous carbohydrates (NFC). The results indicated that foliar Mg application did not influence biometric traits, biomass production, or the structural and protein fractions (NDF, ADF, lignin, and CP). Regarding leaf nutritional status, the concentrations of macronutrients (Mg, N, P, and K) and micronutrients (Mn, Fe, and Zn) remained unchanged, except for calcium (Ca) and copper (Cu). The application at tillering resulted in the highest Ca concentration (8.49 g kg⁻¹), whereas the sequential application at tillering and stem elongation produced the lowest Ca concentration (5.86 g kg⁻¹), indicating partial ionic antagonism during foliar nutrient translocation. Significant differences were observed for NFC content. The sequential application at tillering plus stem elongation resulted in the highest NFC concentration (21.62%), exceeding the other management strategies by up to 63.94%. Under irrigated conditions, foliar magnesium supplementation was not effective in increasing black oat biomass production; however, sequential applications at tillering and stem elongation are recommended to maximize bromatological quality, producing hay with greater energy value. Further studies addressing economic feasibility, production costs, and animal performance are recommended to support decisionmaking regarding the adoption of foliar magnesium supplementation in irrigated black oat production systems.