Análisis de crecimiento estacional de una pradera asociada alfalfa-pasto ovillo Seasonal growth analysis of alfalfa-orchard grass swards

The aim of the present study was to determine a seasonal growth curve in order to define the optimum harvesting time of an alfalfa - orchard grass sward during the different seasons of the year. To this end, a seasonal growth analysis was carried out. Twenty four (24) plots (3 x 3 m) were allocated in a completely randomized design with eight treatments and three replicates; treatments consisted of successive cuts at weekly intervals during an eight weeks regrowth cycle at the middle of each season. At the beginning of the trial all plots were cut to 5 cm height and three samples of 0.25 m2 were cut at ground level to determine residual herbage mass. From then on three different plots were harvested each week in the same manner. Cumulative herbage mass, growth rate, botanical and morphological composition, leaf area index and leaf:stem ratio were the evaluated variables. Results showed that the highest cumulative herbage mass (P<0.05) was found at the fifth week of regrowth in spring, summer and autumn and at the sixth week in winter (4540, 3350, 3600 and 2840 kg DM ha-1, respectively). The highest growth rate was recorded at 4 wk of regrowth in spring and summer (P<0.05), and at 3 and 5 wk in the fall and winter seasons (120, 104, 107 and 78 kg DM ha-1 d-1). The highest leaf area index in alfalfa was seen at 5 wk of regrowth in spring, summer and autumn (P<0.05) and at 6 wk in winter (3.5, 2.8, 2.0 y 1.9). Alfalfa was the main component of the sward during the whole period of evaluation.