Carbon Assimilation, Herbage Plant‐Part Accumulation, and Organic Reserves of Grazed ‘Mulato II’ Brachiariagrass Pastures

Abstract

Pasture management, including the control of grazing intensity and fertilization, can trigger plant physiological and morphological responses that affect plant growth and impact stand persistence. The objective of this research was to quantify the effects of three canopy heights (10, 25, and 40 cm), maintained by mimicking continuous stocking, and two N rates (50 and 250 kg ha−1 yr−1) on canopy carbon exchange rate (CER), plant‐part accumulation, and organic reserves of ‘Mulato II’ brachiariagrass hybrid (Brachiaria brizantha × B. decumbens × B. ruziziensis), also known as Convert HD 364 (Dow AgroSciences, São Paulo, Brazil) during two summer rainy seasons in Piracicaba, Brazil. Leaf CER was greater for the 10‐cm height, but canopy CER, plant‐part accumulation, root mass, and root reserves were less in 10‐ than 40‐cm canopies, although this was not associated with stand deterioration after 2 yr. Leaf was the predominant plant part, and leaf accumulation rate increased linearly from 70 to 100 kg dry matter (DM) ha−1 d−1 as canopy height increased from 10 to 40 cm. Increasing N rate from 50 to 250 kg N ha−1 yr−1 affected plant growth, increasing CER, leaf area index, and the rates of leaf, stem, and dead herbage accumulation. The senescence‐to‐growth ratio (S:G) was not affected by N rate, indicating that the increase in rate of dead material accumulation with greater N rate was a result of an increase in the accumulation rates of all plant parts. Taller canopy heights (25 or 40 cm) are recommended for Mulato II under continuous stocking.

Canopy height and N affect herbage accumulation and the relative contribution of leaf categories to photosynthesis of grazed brachiariagrass pastures

“…Nitrogen fertilization affects plant growth and results in increased HA and LAI in pastures, as has been widely reported in the literature for tropical grasses (Braga, Luz, Herling, & Lima, ; Costa et al., ; Freitas, Fonseca, Braz, Martuscello, & Santos, ; Silva et al., ). The increase in N availability affects morphogenetic characteristics, such as leaf appearance and stem elongation rates, contributing to increased leaf and stem accumulation, which in turn contributes to greater HA (Silva et al., ). In vegetative canopies, N is used for the synthesis new leaf area or promotes greater tissue N concentration (Sinclair & Horie, ), both of which may result in greater canopy photosynthesis.…”

“…The application of more N, however, did not affect the relative proportions of leaf categories in the total LAI. In a companion study, an increase in rate of accumulation of leaf and other plant parts components was measured in pastures receiving more N, but the total HM was not affected by N (Silva et al., ). Even though pastures were growing faster due to more N, they were grazed to maintain an almost‐constant canopy height, which may have contributed to stabilize the proportions of leaf categories in the canopy ( p > .05).…”

“…Increased LAI has been associated with greater net canopy photosynthesis rates (Braga et al, 2008;Lara & Pedreira, 2011;Parsons et al, 1988a,b;Pedreira & Pedreira, 2007;Silva et al, 2016b). In the present study, taller canopies (40 cm) showed greater LAI (Table 2) and intercepted~98% of the incoming radiation, which contributed to greater canopy photosynthesis and also greater HAR and HA.…”

Herbage Accumulation and Organic Reserves of Palisadegrass in Response to Grazing Management based on Canopy Targets

“…Silva et al (2016), studying N reserves of Mulato II brachiariagrass (B. brizantha × B. decumbens × B. ruziziensis) in response to canopy height reported no effect of canopy height on root N concentration and pools. The root N pool followed the same trend, and was not affected by grazing strategy (P > 0.05), averaging 3.6 g m -2 .…”

Forage accumulation and nutritive value, canopy structure and grazing losses on Mulato II brachiariagrass under continuous and rotational stocking

“…(Martha Jr. et al, 2012). Combining adapted forage varieties with appropriate grazing management has the potential to improve pasture productivity and persistence, and may also contribute to increase carbon sequestration (Silva et al, 2016b).…”