Effect of cultivar and grazing intensity in spring on shear and compression energies of dry mature subterranean clover (Trifolium subterraneum L.)

Abstract

Twenty-six cultivars of subterranean clover were divided into 3 maturity groups according to the flowering time and sown in 2 blocks with 4 replicates. The plots were grazed under 2 intensities (hard and lax) during the growing season. The proportions of leaf, petiole, stem, and burr before senescence, dry matter digestibility (DMD), herbage availability, and seed yield in summer were measured. The energies required to shear and compress the resultant dry mature plant materials were determined using an Instron material testing instrument. The results showed a large range for shear (11·3-18·2 kJ/m²) and compression energies (2·8-4·6 kJ/kg DM) among the 26 cultivars. Grazing intensity in spring did not affect shear energy (P > 0·05) but increased the compression energy of dry mature subterranean clover by 0·2 units (P < 0·05). The energy required to shear or compress plant materials was highly correlated with herbage availability, flowering time, proportions of leaf and petiole in the sward, and fibre content of the plant materials, with the relationships being modified by grazing intensity in spring. Compression energy was related to DMD of plants (r = -0·7) and shear energy did not account for a significant amount of variation in DMD.