Managing rhodes grass (Chloris gayana) cv. Callide to improve diet quality. 1. Effects of age of regrowth, strip grazing and mulching

Abstract

Two experiments assessed grazing management strategies for irrigated and nitrogen-fertilised rhodes grass (Chloris gayana) cv. Callide pasture. In Experiment 1, the 4 treatments were: (i) open grazing of the entire paddock on a 2-week cycle (Open); (ii) grazing on a 2-week, daily strip-grazing rotation (2); (iii) a 4-week, daily strip-grazing rotation (4); and (iv) a 6-week, daily strip-grazing rotation (6). For treatments (ii), (iii) and (iv), pasture was allocated at 15 kg green leaf dry matter (DM)/cow/d and grass was mulched to a stubble height of 10 cm after grazing. Stocking rates attained were 1.7, 3.7, 3.5 and 3.4 cows/ha for Treatments (i), (ii), (iii) and (iv), respectively. In Experiment 2, pastures were grazed on a 2-paddock 2-weekly rotation [Open (O) and Open+mulching (OM)] or 28-day rotational cycle without mulching (28) or with mulching (28M) after grazing.

There were substantial differences in yield of pasture on offer to cows with different grazing management, but total leaf yield appeared similar, with a mean growth rate of 42 kgDM/ha/d. There were small, but significant differences in pasture quality between treatments, though pastures in unmulched paddocks had lower crude protein and higher NDF levels than those in mulched paddocks. Animals selected strongly for leaf (78%) across all treatments, though stem content increased from 13% in February to 25% in April. Milk yield was not altered by age of regrowth or open grazing, but was reduced (P<0.05) where rotationally grazed pastures were not mulched. This was attributed to the presence of stem impeding access to leaf when pastures were grazed in narrow strips.

The results demonstrate that intensive management of Callide rhodes grass pastures can support a stocking rate up to 3.7 cows/ha, but there are only small animal production differences associated with radically different grazing management routines. Additional operational costs associated with more intensive management of pastures ranged from AUD30 to AUD80/hafor the 18 weeks of the experiment compared with open grazing. In Experiment 2, net marginal returns were AUD0, -38, -145 and 66/ha for the four treatments O, OM, 28 and 28M, respectively.