Características morfofisiológicas e químico-bromatológicas do capim-aruana adubado com farelo de mamona

Abstract

Brazil has a high livestock production potential based on pastures, whose productivity depends on proper management, mainly fertilization. In this context, castor bean by-products stand out as a sustainable alternative, although they are still little studied as organic fertilizers in tropical pastures. This study aimed to evaluate the use of castor bean meal as an organic fertilizer on Aruana grass (Megathyrsus maximus cv. Aruana), focusing on its morphophysiological and chemical-bromatological characteristics. A completely randomized design was adopted, with different doses of castor bean meal (0, 25, 50, 75, and 100 g per pot) and five replications (10 dm³ pots). Two 30-day production cycles were evaluated. Data were subjected to normality (Shapiro–Wilk) and homoscedasticity (Levene) tests to verify the basic assumptions for analysis of variance. Subsequently, the results were analysed using analysis of variance and regression analysis. In the regression analysis, model selection was based on the significance of linear and quadratic coefficients using Student’s t test (P < 0.05), with the SAS software as a statistical analysis tool (SAS Institute, 2015). In the first cycle, a positive linear response was observed for leaf elongation rate (LER), total leaf senescence rate (TLSR), canopy height, number of new leaves (NNL), total harvestable forage biomass (THFB), harvestable green leaf biomass (HGLB), harvestable green stem biomass (HGSB), harvestable dead forage biomass (HDFB), and crude protein (CP) as castor bean meal doses increased. Tiller population density (TPD) and relative chlorophyll index (RCI) showed quadratic responses, reaching maximum values of 46.34 tillers and 38.18 SPAD units at doses of 71.58 g and 83.31 g, respectively. Mineral matter (MM) content also showed a quadratic response, but negative, with a minimum value of 8.65% at the dose of 59.75 g. Reductions were observed in neutral detergent fiber (NDF) and acid detergent fiber (ADF) contents. In the second cycle, changes in plant response were observed: although total forage biomass, green leaf biomass, green stem biomass, dead forage biomass, and canopy height maintained a positive linear increase, the leaf-to-stem ratio (L/S) and mineral matter content showed a negative linear effect. Dry matter (DM) and crude protein (CP) exhibited positive and negative quadratic effects, with maximum and minimum values of 25.58% at 51.71 g and 5.98% at 36.75 g, respectively. Acid detergent fiber (ADF) and stem elongation rate (SER) showed positive linear behavior. It is concluded that castor bean meal is an efficient organic fertilizer, and a dose of 11.587,10 kg ha⁻¹ is recommended, determined from the average of the maximum values observed for TPD, and RCI, which showed positive quadratic responses. This dose optimizes productive characteristics; however, appropriate management regarding application frequency is essential to maintain production stability and pasture quality over time.