Spatio-temporal variability of palisadegrass-forage peanut pasture structure under continuous stocking

Abstract

The use of grass-legume mixed pastures has been a promising alternative, allowing nitrogen input through biological fixation. Palisadegrass (Brachiaria brizantha [syn. Uruchloa brizantha] cv. Marandu [Hochst. ex A. Rich.] Stapf), a forage with an erect growth habit and clonal propagation mechanism, and forage peanut (Arachis pintoi Krapov. & W.C. Greg.), a stoloniferous legume, also with the same propagation mechanism, are genotypes alternatives with potential to be compatible in mixtures. Canopy structure descriptions in mixed pastures are essential to understand the development and competition processes between plants. Thus, ecology studies in grass-legume mixed pastures can anchor strategies in favour of canopy stability. The objective of this study was to evaluate the spatial variability of structural and morphogenic characteristics and plant ecology in a palisadegrass-forage peanut mixed canopy submitted to herbivory by beef cattle under continuous stocking. The experimental area (1 ha) was managed to maintain the canopy average height between 20 - 25 cm during the rainy season. Nellore heifers weighing 214 ± 17 kg BW and 11 ± 3 months in age were used for stocking. A permanent sample grid was established in the area with 50 georeferenced points, around which the assessments were performed. Canopy structure (average and maximum canopy and legume heights, biomass, tiller and stolon population densities, shade zone, light interception, LAI and botanical composition) were evaluated, as well as morphogenesis (leaf appearance, elongation and senescence rates in both species, and stem and stolon elongation rates) and morphological structure (leaf and stem length [palisadegrass], leaf area and petiole, internode and stolon lengths [forage peanut]). Sampled data interpolation by season was performed by ordinary kriging. Pearson's correlation coefficients between canopy height and the other variables were calculated. There was a spatial dependence structure in all variables. However, in some variables, spatial autocorrelation was not detected during some seasons. The spherical model best explained the semivariogram shape. Variations in canopy height influenced structural and morphogenic characteristics, in which competition for light caused legume etiolation (greater petiole, internode and stolon lengths) in areas with higher canopy height. Forage peanut changed its growth direction under greater shading, developing perpendicularly to the soil surface. Palisadegrass tiller population density responded positively and linearly to canopy height variations. In regions of lower canopy heights, the legume proliferated close to the soil surface, increasing its stolon density and biomass, even in those extremely low areas. Despite such variations, the canopy structure tended to homogenize over time. The results indicate that plant community is affected by variations in canopy height over space. Taller canopies cause competition for light between plants. Under these conditions, grass was favored, unlike the legume, which had its proportion declined community. On the other hand, in places with lower canopy height, forage peanut is benefited, as it is stimulated to develop by clonal propagation.