Duration of rest period and canopy growth of Panicum maximum cv. Mombaca under intermittent stocking

The canopy growth of Mombacagrass was assessed under intermittent stocking with three rest periods, characterized by the time required for the expansion of 2.5, 3.5, and 4.5 new leaf blades per tiller, after grazing periods of six days. The experimental area was divided into five or six paddocks per treatment. Five crossbreed (Holstein x Zebu) steers were randomly assigned to each treatment. Extra steers were also used to achieve residual leaf area index of about 2.0, by the end of each grazing period. Two Growth phases were considered: I) after standardization cut at the beginning of the growing season, and 2) after some grazing cycles had taken place, under the effects of the experimental rest periods. The paddocks received broadcast fertilization of N, P2O5 and K2O (50, 12.5 and 50 kg/ha) in the beginning of the growth phases 1 and 2. Photo synthetically active radiation (PAR) interception, leaf area index (LAI) and green forage dry mass (GFDM) were assessed over 45 days of regrowth, at six day intervals. Second order polynomials were adjusted to GFDM and LAI data, as a function of canopy ages. From these equations, instantaneous values of GFDM and LAI were estimated, from which it was derived the instantaneous values of relative growth rate (RGR) and net assimilation rate (NAR), respectively for each canopy age. PAR interception by the canopy increased in an asymptotic manner, reaching critical values of 95 - 98%, while LAI and GFDM values increased in the stability range of PAR interception. The growth indices RGR, NAR and LAR showed decreasing asymptotic evolution. The great proportion of stem in end of the longest rest period favored the decrease in RGR and NAR values.