Effects of daily herbage allowance on the organic reserves at the end of grazing and the accumulation of herbage during regrowth

Abstract

The effects of daily herbage allowance during prior grazing on the consequent regrowth of Lolium perenne were measured throughout 3 experimental periods. Morphological structure and organic compounds in the residual sward were analysed at the end of grazing, and herbage mass measured during regrowth period. About 29%, 35%, and 52% of the biomass offered was removed by grazing in high [44 kg organic matter (OM)/cow.day], medium (30 kg OM/cow.day), and low (19 kg OM/cow.day) herbage allowance plots. The proportion and density of live lamina in the post-grazing swards linearly decreased with decreasing herbage allowance. The density of sheath plus dead materials increased slightly or remained at the high and medium herbage allowances, whereas 17% of these materials was removed at the low allowance. Herbage allowance had a significant effect on the contents of organic compounds (total N, soluble proteins, reducing sugars, fructans) in the residual live lamina and sheath, without significantly (P < 0.05) affecting those in the roots. Reducing sugars were the largest pool of organic reserves in residual tissues. The pool size of organic reserves in live lamina decreased in parallel with the residual biomass of this tissue in response to herbage allowance. A large portion of organic reserves, especially for fructans, was found in the sheath. The quantity of organic reserves in the residual sheaths was not significantly (P > 0.05) different with high or medium allowances, but tended to be lower with the low allowance. The organic reserves in live lamina had a higher significance for the first 6 days of regrowth, while those in remaining sheath were more important in the later stages of regrowth.