Dinâmica de produção de forragem e valor nutricional de gramíneas nativas submetidas a distintos períodos de diferimento

Abstract

The natural grasslands of the “Pastizales del Rio de la Plata” are ecosystems that present great physiognomic heterogeneity, mainly due to the diversity of plant species that compose them, where up to 80% of the forage mass is made up of C3 and C4 grass species. This greater participation of C4 grasses (summer) causes a reduction in forage production in the autumn and winter period. Furthermore, the occurrence of droughts in the summer can also reduce the primary productivity of these areas. Forage stockpiling is an efficient tool to reduce the effects of productive seasonality as its main objective is to allow the accumulation of forage for future use in periods of lower production. However, this practice has the main drawback of reducing the nutritional value of the forage. as the grazing exclusion period progresses. Knowledge of the responses of native species to different stockpiling periods is essential to promote efficient use of natural pastures aimed at more productive livestock farming, since the processes of plant growth and senescence are related to the nutritional value of the forage. The present study aimed to evaluate the forage accumulation capacity and variation in the nutritional value of native species from different functional groups and different metabolic routes in increasing periods of pasture stockpiling at different times of the year. Five stockpiling intervals (450, 900, 1350, 1800 and 2550 ºC) and six grass species (Andropogon lateralis, Bromus auleticus, Mnesithea selloana, Nassela neesiana, Paspalum dilatatum and Paspalum Notatum) were evaluated in stockpilings from spring to summer and autumn. to winter. Forage mass increased throughout the stockpiling intervals, especially in stockpilings from spring to summer. The main factors related to the nutritional value of native grasses were the percentage of green leaves that increased the nutritional value, while the stockpiling time and forage mass had a negative impact on the crude protein (CP) and digestible energy (DE) contents of the forage. A important effect of the type of grass species was observed on the evolution of the forage mass/nutritional value ratio. Based on the results of this study, under non-limiting conditions of soil fertility and humidity, in stockpilings from spring to summer, species with a winter cycle (N. neesiana and B. auléticus) could be subjected to stockpilings of 100 days, A. lateralis of 80 days, P. Notatum and M. selloana of 60 days, and P. dilatatum of 40 days. In autumn to winter stockpilings, N. neesiana and B. auléticus could be stockpiled for 100 to 120 days, A. lateralis, P. dilatatum and M. selloana for 70 days in early autumn, , while P. Notatum is not suitable for autumn to winter deferrals due to loss of nutritional value.