Establishment and implantation efficiencies of temperate pastures with different sowing densities and nitrogen fertilization moments

GATTI, M.L.; AYALA TORALES, A.; PUSSETTO, D.; DOESWIJK, F.; CIPRIOTTI, P.A.; GOLLUSCIO, R.A.

Rosario, Argentina

Congreso; IX International Rangeland Congress; 2011

Mixed temperate pastures should temporally be used as a winter crop by means of increasing sowing densities of the annual grass species and applying strategic nitrogen fertilizer. But higher sowing densities of the annual grass might contribute to perennial grasses and legumes displacement, modifying the floristic composition and the community stability. The aim of this study was to estimate establishment and implantation efficiencies resulting from two relative sowing densities of the annual and perennial grasses, and three fertilization treatments. A pasture composed by four species: Bromus willdenowii Kunth (-BW- annual grass), Dactylis glomerata L. (-DG-perennial grass), Trifolium pratense L. (-TP-) and Trifolium repens L. (white clover -TR-) was sown in the experimental field of FAUBA; 50 % of C3 grasses, 30 % of TP and 20 % of TR, on about 1700 viable seeds/m2. Sowing arrangement consisted of alternate rows of grasses and red clover, 0.175 m apart, with annual and perennial grasses in the same row and white clover sown in coverage. Twenty four experimental units of 6 m2 were established in a factorial arrangement of two relative sowing densities (35%DG+15%BW (>DG); 35%BW+15%DG (>BW)) and three fertilization treatments (without nitrogen and with 170 kg N.ha-1 in autumn or in winter) arranged in a randomized complete block design (n=4). Study variables were plant density (number of seedlings or plants/m2 -nº/m2-) registered in a fixed subplot of 0.09 m2 and sowing efficiencies (%) estimated by as the proportion of viable sown seeds.m-2 that performed in established seedling and implanted plants, two months and one year after sowing, respectively. Analyses of variance with a signification level of 5 % were used. The effects of fertilization and fertilization*density interaction were not significant on the evaluated variables. Grasses establishment efficiency was increased associated to lower sowing density of the annual component BW, which expressed minor establishment efficiency when it was sown at higher density (Table 1). In >DG treatment, it was observed a higher density of both grasses seedlings and three times the number of DG seedlings; 106 BW seedlings/m2 were established, independently of the initial sowing density, suggesting a limit imposed by intraspecific competition. In spring, many BW plants bloomed and died, so differences in their implantation efficiency were increased, also in the overall efficiency of the grass functional group (Table 1). Independently of initial densities, around 32 DG pl/m2 were registered; probably plant death has been increased in dense pasture during summer period. Nevertheless, the density of grass plants increased with higher sowing densities of the perennial one. Variables under study were not modified in legumes group. It is concluded that lower relative sowing density of the annual grass improved its own establishment and implantation efficiencies and those of the perennial one and grass component.