Controles biofísicos e ambientais da evapotranspiração em pastagens tropicais sob condições de sequeiro

Abstract

Pastures cover about 25% of the global area, making it larger than any other land use. In Brazil, it is equivalent to 32% of the total area used by agriculture, and predominantly for livestock production, which presents itself as a strategic sector in guaranteeing food security, which is seriously threatened by climate change. Evapotranspiration (ET) is the main requirement for developing strategies to improve water use in agriculture, as it is the main driver of energy balance partitioning and influences hydrological and carbon cycles at global, regional and local scales. Furthermore, there is a close relationship between ET and rainfall, especially in tropical environments. Therefore, the objective of the present study is to evaluate how the ET of a tropical pasture under grazing conditions responds to seasonal and interannual variability in meteorological forcing. The data came from an experimental campaign in an area grazed (Brachiaria brizantha) by sheep at the Escola Agrícola de Jundiaí. Energy balance and ET data were collected using the eddy covariance (EC) method and analyzed based on data from two agricultural years (2015-2016 and 2016-2017). To evaluate the effect of meteorological forcing and vegetated surface on ET, canopy conductance (Gs), the omega decoupling factor Ω and the Priestley-Taylor factor () were determined. ET showed pronounced seasonality, closely aligned with the seasonality of rainfall. Lower daily averages were observed during the dry season in both agricultural years (1.01 ± 0.60 and 0.89 ± 0.44 mm, respectively). observed in the rainy season (2.44 ± 0.75 and 4.83 ± 0.96 mm, respectively). Precipitation presented a negative (-59 mm) and positive (356 mm) anomaly during the years studied, respectively. Gs patterns and the significant correlation between Gs, Ω and  (p < 0.01) indicate that surface control prevails over atmospheric control on an annual scale. This relationship is probably induced by a stomatal vegetative control mechanism, which protects. vegetation against excessive water loss during periods of high temperatures and low humidity levels.