SEASONAL GROWTH CURVES OF PERENNIAL RYEGRASS

Abstract

In order to evaluate the seasonal pattern of growth of perennial ryegrass (Lolium perenne L.) in the temperate zone, an experiment was carried out in an irrigated sward at Colegio de Postgraduados Research Station at Montecillo, Texcoco, México. The treatments were successive cuts made at seven day intervals during a regrowth period of 8 weeks, allocated in a completely randomized design with three replicates, in the four seasons of the year between 1998 and 1999. At the begining of the trial 24 plots (3 x 3 m) were cut to 5 cm and three samples of 0.1 m² were taken to ground level to determine residual herbage mass; from then onwards, every week three different plots were harvested in the sane way. Differences in cumulative herbage mass, botanical and morphological composition, the green leaf:stem ratio, the green-leaf:not leaf ratio, leal crea index (LAI) and growth rate (GR) were analyzed statistically with PROC Mixed and GLM of SAS for repeated measurements. Total cumulative herbage and GR increased rapidly from a low level immediately after defoliation, and eventually reached an equilibrium level as the amount of green leal in the sward was highest. Spring production (1983 kg DM ha^-1) was 16, 39 and 63 % higher than Summer, Autumn and Winter, respectively. The time
required to reach this status varied seasonally, with the number of cuttings ranked as follows: Spring (4 weeks), Summer (5), Autumn and Winter (6). Once the sward reached this point, GR started to decline as a consequence of an increase in dead material and stem. These increases were highest in spring and lowest in winter. The results of this study suggest that ryegrass sward management to maximize herbage production and utilization must be done once that the highest green leal mass is reached. In this trial, such a stage was reached at 5, 6, 6 and 4 weeks in Summer, Autumn, Winter and Spring, respectively.