Estudio de la resiliencia productiva del campo natural bajo intervenciones de largo plazo post estrés hídrico estival

The experiment was conducted at the Mario A. Cassinoni Experimental Station (Faculty of Agronomy, Udelar) in Paysandú, Uruguay. The resilience of natural grassland after experiencing summer water stress and its productive response to nitrogen fertilization and the introduction of legumes were evaluated. The study covered two subperiods: autumn–winter (May 10, 2023 – July 18, 2023) and winter–spring (July 19, 2023 – September 25, 2023), under a rotational grazing system (15 days of grazing and 45 days of rest). The experimental design was a Randomized Complete Block Design (RCBD), divided into four blocks, each containing four plots. Four treatments were evaluated: an untreated control (CN), improved natural grassland with legumes (CNM), and nitrogen fertilization at 60 kg N/ha/year (N 60) and 120 kg N/ha/year (N 120), applied in the autumn–winter period. All treated plots received 40 kg/ha/year of P₂O₅ in autumn. Variables directly measured included pre-grazing and post-grazing dry matter, as well as the height of pre-grazing and post-grazing dry matter. Based on these data, additional variables were calculated: available, disappeared, and produced dry matter, daily growth rate, botanical composition (including fourteen plant groups), total stocking rate, average daily gain, meat production per hectare, and forage supply. Mean comparisons were carried out using Tukey's test and orthogonal contrasts. According to Tukey’s test, considering the entire study period, total dry matter production was significantly higher in the treatment with 60 kg N/ha (N 60) compared to the other treatments. Regarding the daily growth rate, no significant differences were observed among treatments. Biomass production was significantly higher in the winter–spring subperiod compared to autumn–winter. Average daily gain did not differ significantly between treatments. Total meat production was higher in the nitrogen treatments and in CNM, with the nitrogen treatments showing the highest absolute values; however, no statistical analysis was performed for this variable due to lack of replication. CNM appears to be a viable alternative to improve the productivity of natural grasslands.