Renovation of pastures containing paspalum. 3. Effect of defoliation management and irrigation on ryegrass growth and persistence

Ryegrass seedlings were introduced into areas with high (Pa) or low (NPa) contents of paspalum. Their growth and persistence was monitored from August 1981 until May 1982. The effects of grazing interval, irrigation, and competition from resident species on growth of the introduced ryegrass plants were determined. Total losses of ryegrass plants were highest in summer (75%) and 'animal effects' (i.e., severe grazing, 'pulling', dung and urine deposition, trampling) accounted for 51% of the total losses. Clipping resident herbage surrounding introduced ryegrass plants increased their size (tillers/plant) by 230 - 300% from January to April. This was accompanied by a three-fold reduction in plant deaths during summer - autumn. Summer irrigation did not improve ryegrass survival. Plants grazed at short intervals over spring - summer were smaller and suffered more damage and deaths than did plants grazed at long intervals. During late summer more deaths of ryegrass plants occurred in Pa than NPa plots but in autumn this effect was associated with the extra stress of a short grazing interval. Reducing the competitive environment for the introduced seedlings during early growth, to allow the attainment of a large size (20 - 30 tillers/plant) before the onset of summer stresses, was necessary to enhance ryegrass survival.