Respuesta a la intensificación productiva del campo natural en el período otoño-invernal

The present study was conducted at the Mario A. Cassinoni Experimental Station of the Faculty of Agronomy of the University of the Republic, located at kilometer 363 of General Artigas Route, in the department of Paysandú, Uruguay, more precisely in an area of 10.3 hectares that are part of paddock number 18 (32° 23' 57" South latitude and 58° 2' 42" West longitude). The evaluation period was between May 9, 2022, and September 30, 2022. This period, which lasts approximately 5 months, is divided into two sub-periods: autumn (May 28, 2022, to August 1, 2022) and winter (August 2, 2022, to September 30, 2022). The objective of the work was to evaluate the autumn-winter productive response of the natural pasture subject to different intensification treatments, managing a target forage offer of approximately 8% LW for both seasons under rotational grazing with 15 days of occupation and 45 days of rest. The experimental design was a randomized complete block (RCBD) with split plots in time, with four replications. The treatments were: a control without intervention (CN); natural pasture improved with legumes, specifically Lotus tenuis cv. Matrero and Trifolium pratense cv. Estanzuela 116 (CNM); and two levels of nitrogen fertilization, 60 kg/ha/year (N 60) and 120 kg/ha/year (N 120) applied in autumn-winter. Additionally, the three intervened treatments are annually fertilized with 40 kg/ha/year of P2O5 in autumn. An analysis of variance between treatments was performed, as well as orthogonal contrasts. The variables analyzed were: present dry matter, available dry matter, remaining dry matter, height of available and remaining forage, daily growth rate, dry matter produced, dry matter disappeared, and utilization percentage. Additionally, a study of botanical composition was carried out with the presence of fifteen botanical groups, percentage of green forage, percentage of bare soil, percentage of soil covered by weeds, total load, average daily gain, meat production per hectare, and forage offer. The study indicates that treatments with added nitrogen fertilizer showed superiority in dry matter production and growth rate, with similar results between the 60 N and 120 N doses. CNM presented intermediate values in these variables. Treatments with added external inputs showed lower contributions from perennial species but no differences in annual species. Biomass production was higher in autumn, but forage quality was better in winter due to a change in botanical composition. Regarding secondary production, it was found that average daily gain did not differ between treatments with added inputs, but it did with the control, and that nitrogen treatments and CNM presented high total meat production, with nitrogen treatments being superior. However, the use of 120 N and 60 N did not differ in productivity, and CNM is an interesting option to increase natural pasture limitations.