Effect of irrigation threshold on the water productivity of second-year grazed alfalfa

Abstract

As a consequence of climate change, drought periods are becoming increasingly frequent, which leads to a significant decrease in forage production, exacerbated by the low water- holding capacity of soils in Uruguay. There is uncertainty in determining the volumes and timing of irrigation to maximize the use of precipitation without the crop limiting evapotranspiration or doing so within certain limits to ptimize water productivity.

The objective was to determine the irrigation management in terms of the amount and timing of water applied that best suits alfalfa under grazing. The trial was conducted at the South Regional Center, Faculty of Agronomy – Udelar, Uruguay, on a Medicago sativa cv Chaná pasture. The treatments were: rainfed (T0), irrigation when 30% of available water was depleted (T30), and irrigation when 65% of available water was depleted (T65). The timing of irrigation was determined by water balance, accompanied by soil moisture measurements using the FDR probe to verify irrigation thresholds. Grazing entry was determined based on the criterion of 8 knots on the main stem. There were significant differences in the second summer of evaluation in favor of the irrigated treatments. The T65 proved to be the most efficient alternative for pasture water management. There was no response in biomass increase above 500 mm per year of water consumed by the crop, with a maximum yield of 23,500 kg of DM ha⁻¹.