Abstract
The objective of this experiment was to evaluate the nitrogen and plant density influence on the yield, forage dissection and nutritive value of Tanzania grass (Panicum maximum Jacq.). The design was of completely randomized blocks with three replications in a factorial arrangement with four nitrogen levels (0, 80, 160 or 320 kg/ha N) and three plant densities (9, 25 or 49 plants/m2). The plots were cut at 25 cm from soil level when the canopy reached 95% of light interception. The total dry matter forage yield and dry matter forage yield per harvest increased linearly with the nitrogen fertilization. The leaf and stem yield had the same response. The senesced forage yield was quadratically influenced by the nitrogen. The stems ratio in the morphologic composition was high in the high nitrogen levels and in the low plant densities. The leaf:stem ratio showed high values in this trial, but it was increased in plots without nitrogen and high plant density. The pre-grazing height was reduced with the increase in plant density. The nutritive value was favored by the nitrogen fertilization, which increased the crude protein level and reduced neutral detergent fiber and lignin. These factors increased the leaf and stem in vitro digestibility of organic matter. Nitrogen fertilization increases the forage yield of Tanzania grass under rotational grazing. After the establishment, plant density has little influence on the Tanzania grass yield and its forage dissection. The harvest with 95% light interception improves the structure and nutritive value of Tanzania grass pastures.
Highlights
It is estimated that 22% of the national territory is occupied with pastures (IBGE, 2006), and that approximately 90% of the nutrients required by ruminants are originated from pasture (Euclides et al, 2010)
As an alternative to the traditional recommendations of managements, the concept of light interception established in the study of management of temperate forages may be applied to the tropical forages (Hodgson & Da Silva, 2002)
At a dose of 320 kg/ha N, plants were harvested, on average, 5.3 times, whereas in the absence of N, there were 2.9 harvestings over the experimental period. This is a result from the effect of N increasing tissue flow (Braz et al, 2011) and the accumulation of biomass on the pasture, which anticipated the interception of 95% of light by the canopy, increasing, the number of harvestings and decreasing their interval
Summary
It is estimated that 22% of the national territory is occupied with pastures (IBGE, 2006), and that approximately 90% of the nutrients required by ruminants are originated from pasture (Euclides et al, 2010). The production indexes of Brazilian cattle farming are below its potential, probably due to the adoption of arbitrary measures at the management of pasture, such as stocking rate, grazing pressure, and mainly, number of regrowth days. Due to the variations in the growth rates of pasture and the seasonality of production, the use of fixed grazing cycles, for example, may result in early or late harvesting, factors that impair growth and/or degrade the pasture structure (Voltolini et al, 2010). As an alternative to the traditional recommendations of managements, the concept of light interception established in the study of management of temperate forages may be applied to the tropical forages (Hodgson & Da Silva, 2002). In systems of intermittent stocking, the pre-grazing condition in which the pasture intercepts 95% of the light corresponds to the maximum net growth of the forage plant. The latter presents structure and nutritional value that favor the intake of forage by animals (Carnevalli et al, 2006)
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