Seasonal herbage accumulation, plant-part composition and nutritive value of signal grass <i>(Urochloa decumbens)</i> pastures under simulated continuous stocking

Abstract

In order to optimize the regrowth and harvest of signal grass (Urochloa decumbens) cv. Basilisk pastures it is necessary to establish more precise grazing management guidelines. The objective of this study was to evaluate herbage accumulation, plant-part composition and nutritive value of signal grass managed under contrasting levels of steady-state canopy heights. Treatments included 3 canopy height targets, i.e. 10 (S-short), 17.5 (M-medium) and 25 cm (T-tall), in a completely randomized design with 4 replications. Experimental units were 144-m2 plots which were grazed by groups of steers for short periods in an endeavor to keep canopy heights at the 3 desired targets. On average, herbage accumulation rate (HAR) in T pastures was greater than in M and S pastures, including the dry-wet season transition period in spring (September‒November). The S pastures had higher crude protein and lower acid detergent fiber concentrations than M and T pastures, especially in the first half of the calendar year. However, in vitro organic matter digestibility was similar for all treatments (612 g/kg). As S and M pastures had lower HARs than T pastures in the spring, it appears advantageous to maintain the signal grass canopy at ~25 cm in order to ensure quick regrowth with the return of the wet season. However, longer-term studies are needed with recording of animal performance before these initial findings can be promoted widely.