Components of regrowth in grazed and cut <i>Lolium perenne</i> swards

Abstract

Abstract Growth measurements were made on Lolium perenne ‐dominant vegetative swards during 4‐week regrowth periods following grazing or cutting. In the grazing study, the ryegrass ( Lolium perenne ) swards were grazed for 12‐d periods with stock numbers set according to initial herbage allowances per animal of 16, 32 and 64 kg organic matter per sheep. One area was grazed in summer and another area in the autumn. In the cutting experiment four ryegrass swards growing in boxes were prepared by cutting to either 2 or 6 cm at either 14‐ or 28‐d intervals. The swards were cut back in autumn to 2 or 6 cm. During the regrowth period half the boxes were retained in full light and half shaded to 48% of incident light. Herbage weight, rates of leaf extension, senescence, leaf appearance and tillering, water soluble carbohydrate reserve levels in tiller bases and, in the cutting experiment, sheath tube lengths and lamina lengths of leaves which had grown through the sheath tube were measured at intervals during the regrowth period. Final herbage weights reflected management history but net herbage accumulation over the four‐week regrowth period, though affected by season, pretreatment and light level, was similar on swards subjected to different grazing or cutting treatments. This result was partially explained by changes in the balance between growth and senescence per tiller as herbage weight increased with time during regrowth, and partially by the reduced production per tiller in harder‐grazed swards being offset by a rapid increase in tiller numbers. There was a positive curvilinear relationship between lamina length and the length of the sheath tubes through which the laminae emerged. Carbohydrate reserve levels declined rapidly after grazing or cutting, the extent of the decline being related lo the severity of the defoliation. Recovery commenced after four days in summer and was complete within 3 weeks but reserve levels remained low in plants grazed or cut in autumn. The need is discussed for more detailed descriptions of sward states in management studies and for more information on component processes of growth, the factors affecting them and how these interact with different kinds of management systems.