Abstract
In Campos grasslands, the production of forage and its variability are driven by the amount of rainfall. In this context, stockpiling forage from spring to summer is a useful tool to maintain the feed supply for livestock, but so far it has not been developed due to the lack of information for farmers decision-making. In this paper we evaluated the response of pasture production to spring grazing deferment in a shallow basaltic grassland in 12 combinations of lime (0 and 1500 kg ha-1 of CaMg(CO3)2), phosphorus (0 and 90 kg ha-1 of P2O5) and nitrogen (0, 75, 150, and 300 kg ha-1 of N, except in the upper two N levels that were evaluated only with lime) addition. Forage accumulation, sward height and nitrogen nutrition index (NNI) were evaluated every 15 days during 75 days. Both sward height and available forage mass increased linearly with the deferment time. The lime application did not affect the forage accumulation rate, while the single nitrogen and phosphorus addition only showed a slight positive effect, however the combined addition of N-P fertilization tripled the forage production. Nitrogen fertilization improved the NNI and was further enhanced by the combined application of N and P. Our results suggest that the capacity of shallow basaltic grasslands to accumulate deferred forage is co-limited by N and P availability.
Highlights
Optimizing productivity and use of natural grasslands is considered a strategic way to conserve them
Since natural grasslands in shallow soils are regularly limited by its low water storage capacity, fertilization can be ineffective, especially if the fertilizers are applied during the water deficit period
This study aimed to evaluate the response of pasture production to spring grazing deferment in a shallow basaltic grassland in different conditions of liming, phosphorus and nitrogen addition
Summary
Optimizing productivity and use of natural grasslands is considered a strategic way to conserve them. Since natural grasslands in shallow soils are regularly limited by its low water storage capacity, fertilization can be ineffective, especially if the fertilizers are applied during the water deficit period This situation, common in the north of Uruguay and part of Rio Grande do Sul, Brazilian state, limits the pasture growth in summer due to low water availability in soils, inducing to overgrazing. The Campos grasslands situated on shallow basaltic soils exhibit high vulnerability to droughts The heterogeneity of these grasslands was classified by Lezama[5] highlighting the availability of water as the main factor explaining the environmental control of floristic and functional gradients. In these conditions, the overgrazing and the absence of management practices to minimize the edaphoclimatic constraints cause important environmental and productive losses[6]
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