Agronomic performance of an association of Morus alba (Linn.) with Panicum maximum under simulated grazing conditions

María Gabriela Cristina Medina Rivera

ABSTRACT
In order to study the agronomic performance of an association of Morus alba (Linn.) with Panicum maximum, under simulated grazing conditions, a trial was conducted with 4 x 3 x 3 factorial arrangement and three repetitions per treatment on a Ferralitic Red soil. The evaluated factors were the successive rotations, the distance between rows (1, 2 and 3 meters) and the pruning height in the tree (10, 100 and 200 cm). Significant differences (P<0,05) were observed in the area covered by the pasture in favor of the final stage (84 %), as compared with the initial one (69 %). Yet, the weeds and the depopulated area significantly decreased (3,6 vs 1,7 % and 9,1 vs 0 %, respectively) and the creeping legumes and natural pasture did not show noticeable variations. The percentage of creeping legumes was higher in the distance of 2 and 3 m (2,3 and 2,5 %) with regards to 1 meter (0,6 %) and the pruning height did not create any variation in the pastureland indicators. The pasture height was higher in the first and last rotations (112 and 126 cm, respectively), and the DM availability was maximal in the first rotation with 4,7 t DM/ha. These indicators did not show significant variations with the distances between rows and the pruning height in the tree. The total biomass availability of M. alba showed substantial differences in favor of the first two rotations (1,24 t DM/ha), performance also observed in the edible biomass (1,12 t DM/ha). The pruning height in the tree did not cause any change in the total biomass availability or its components; however, the 1-m distance between rows provided the highest availability (1,48 t DM/ha). On the other hand, the number of branches increased significantly with the rotations (7 to 14); similar performance was shown by the stem diameter (1,7 to 2,5 cm). The distance between rows did not cause noticeable variations in these indicators. Nevertheless, higher diameters and branch numbers were observed in the plants pruned at 200 cm (1,2 to 2,8 cm and 7 to 12 branches, respectively). The survival of M. alba was significantly affected with the successive rotations and in all the evaluated factors the final survival (65 %) was significantly lower (P<0,05) than in the initial stage (100 %). On the other hand, the highest plant losses were observed in the 1-m distance (3 397 plants/ha) and the 10-cm height (3 351 plants/ha). The association of M. alba and P. maximum under simulated grazing, allowed a mean availability of 2,5-4,7 t DM/rotation and 0,4-1,2 t DM/rotation of the pasture and the tree, respectively. The 1-m distance between rows and the pruning height of 10 cm should not be used because they cause a lower survival of the M. alba population.