Efecto de la fertilización nitrógeno-fosfatada y de la incorporación de leguminosas en campo natural sobre la composición botánica y la producción primaria y secundaria

This study was conducted in paddock 18 of the Mario A. Cassinoni Experimental Station at the Faculty of Agronomy, located in the Paysandú department, Uruguay (-32º39’96’’ S, -58º04’45’’ W). The experiment, established in 2014, has undergone management monitoring, including grazing practices and the addition of inputs, as well as a potential residual effect from these inputs. The evaluation period spanned from April 2, 2024, to July 22, 2024, encompassing 111 days divided into two complete grazing cycles: Cycle 1 (April 2, 2024, to May 27, 2024) and Cycle 2 (May 27, 2024, to July 22, 2024). The objective of the study was to assess two intervention technologies in natural pasture: nitrogen-phosphorus fertilization and the introduction of Lotus tenuis and Trifolium pratense along with phosphorus application. The effects measured included dry matter (DM) production, botanical composition, and secondary production. The treatments were as follows: control without intervention (NP), improved natural pasture with legumes and the addition of 40 kg P2O5/ha (INP), and two levels of nitrogen fertilization: 60 kg/ha/year (N60) and 120 kg/ha/year (N120), split equally between autumn and winter, along with the addition of 40 kg P2O5/ha. These treatments were arranged in a completely randomized design with four replications.  For each variable considered, an analysis of variance and orthogonal contrasts were performed. These variables included the height of available dry matter (DM), available DM, percentage of available green matter (GM), height of residual DM, residual DM, percentage of residual GM, percentage disappeared, accumulated production, and growth rate. Additionally, seventeen botanical groups, percentage of bare soil, percentage of weedy cover (WC), average daily gain (ADG), and percentage of forage supply (FS) were analyzed. The study indicates that no superiority in forage production was observed with increasing levels of intervention, primarily due to unfavorable climatic conditions. Similarly, the addition of inputs resulted in changes in the composition of the sward, favoring high-quality forage species, particularly concerning Lolium multiflorum. This resulted in increases in the ADG of the studied animals, showing significant differences between the CN and N120 treatments, while the other two exhibited intermediate behavior. It is important to highlight that the increase in meat production occurs at the expense of the replacement of perennial species by annuals, which could pose an ecological threat.