Morfologia e produtividade de capins tropicais sobressemeados com aveias com e sem irrigação

Abstract

Irrigation of pastures can be a strategy to improve the quality and productivity of tropical grasslands; however, its long-term benefits remain little studied. Therefore, this research aimed to evaluate the productive and morphological characteristics of Cynodon dactylon cv. Tifton 85, Urochloa brizantha cv. Mg-5, and Megathyrsus maximus cv. Mombaça, overseeded with Avena sativa L. cv. IPR Esmeralda and Avena strigosa Schreb. cv. Iapar 61, under irrigated and non-irrigated conditions, with an application intensity (AI) of 2.14 mm h-1, over two years. The experiment was conducted from May 15 to November 10, 2022 (Year 1) and from May 15 to November 10, 2023 (Year 2), at the Experimental Irrigation Area of the Federal University of Grande Dourados (UFGD). A randomized block design was used, with tropical grasses overseeded with oats, under irrigated and non-irrigated systems, for two consecutive years. The following variables were evaluated: total forage production, morphological characteristics (forage accumulation rate, canopy height, leaf-to-stem ratio, and senescent material percentage), and nutritional attributes (crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), and in vitro dry matter digestibility (IVDMD)). The results presented across the three chapters of this thesis demonstrate that irrigation led to significant increases in total dry matter yield, with average increments of 77.97%, 44.59%, and 133.96%, depending on the species. Irrigation also promoted distinct responses in the leaf-to-stem ratio and in the percentage of senescent material in the grasses. The increased forage accumulation rate (FAR) under irrigation resulted in an average yield of 18.32 Mg ha-1 with irrigation and 10.16 Mg ha-1 without irrigation. Among the species, Tifton 85 was the most productive, followed by Mg-5 and Mombaça, with average dry matter yields of 15.31, 13.96, and 13.47 Mg ha-1, respectively. Studies indicated a reduction in the percentage of senescent material under irrigation, with values of 2.88% and 5.73% in irrigated systems versus 4.82% and 8.11% in non-irrigated systems. Tifton 85 produced more dry matter compared to the other grasses, with increases of 1.98% over MG-5 and 17.00% over Mombaça. The highest leaf-to-stem ratio (LSR) values were observed in the second year (2.86 vs. 3.75), with greater gains under irrigation (3.36 vs. 3.24). The highest LSR was found in Mombaça grass (3.74), decreasing by 8.41% in Mg-5 and 38.52% in Tifton 85. Crude protein (CP) contents did not show significant variations as a function of irrigation. Overseeding with Avena sativa L. cv. IPR Esmeralda and Avena strigosa Schreb. cv. Iapar 61 stood out by significantly increasing productivity and crude protein levels, improving forage nutritional quality by up to 20%. However, differences among grasses were observed: Tifton 85 had the highest CP content (15.54%), corresponding to 8.37% and 13.60% higher protein levels compared to Mg-5 and Mombaça, respectively. Integration of evidence from Chapters 1, 2, and 3 indicates that neutral detergent fiber (NDF), acid detergent fiber (ADF), and in vitro dry matter digestibility (IVDMD) were not significantly affected by irrigation, although differences of 2.77, 2.46, and 2.51 percentage points were observed between irrigated (IR) and non-irrigated (NIR) treatments in areas overseeded with oats, for Tifton 85, Mg-5, and Mombaça, respectively. In summary, the chapters of this thesis highlight that the interaction among water management, overseeding, and grazing constitutes an efficient strategy to intensify forage production in tropical regions, promoting greater productive efficiency, improved animal performance, and sustainability of production systems.