The effect of nitrogen fertilization upon the herbage production of tall fescue swards continuously grazed with sheep. 1. Herbage growth dynamics

Abstract

The efTect of level of nitrogen application upon the dynamics of herbage growth in a continuously grazed sward of tall fescue was investigated during two successive years. In order to obtain a large range of sward structural conditions, the experiments were carried out with two contrasting cultivars: cv. Clarine and cv. Barcel, and, in Year 2, with two different sward heights or leaf area indices (LAls). During each of five experimental periods (2-3 weeks), swards received either optimum (N2) or deficient (Nl) N applications, were maintained at their target LAI, and leaf growth was measured on labelled tillers. With continuously defoliated tillers, N»-shortage had only a small effect on the leaf elongation rate compared with tillers protected by cages. The leaf production per tiller was only slightly reduced by N shortage, and it was mainly by the means of a reduction in tiller density that the N deficiency resulted in reduced herbage growth per hectare. These results indicate that, in continuously grazed swards, in contrast with results previously found in intermittently defoliated swards, leaf elongation is not the only important component of difference in herbage growth and that the promotion of tillering rate is an additional pathway for N response in such management regimes.

Sward structure of marandu palisadegrass subjected to continuous stocking and nitrogen-induced rhythms of growth

“…However, for the same target of sward height, acceleration of the growth rhythm of plants using nitrogen fertiliser resulted in increased total herbage bulk density. This may be the result of the higher rates of leaf elongation on nitrogen fertilised relative to non-fertilised swards (Mazzanti et al, 1994). This was corroborated by the results of a concomitant experiment carried out in the same area involving measurements of morphogenetic responses to treatments imposed (Table 4).…”

Tillering dynamics in pastures of guinea grass subjected to grazing severities under intermittent stocking

“…The amount of forage mass affects tillering (Langer, 1956), in a way that after severe defoliation occurs after inhibition of tillering due to low availability of organic reserves in the plant (Matthew, 1992) (Table 1). This variation coincides with changes in environmental conditions throughout the year (Difante et al, 2008;Pena et al, 2009;Sbrissia et al, 2010), since, in the processes of formation, development, growth and senescence of tillers are influenced by weather conditions (Mazzanti et al, 1994). It is also worth noting that the adoption of a variable postgrazing height throughout the year (50-30 cm) resulted in higher appearance rate of basal tillers in the summer of 2007 (Table 1).…”

Eficiência bioeconômica da adubação de pastagem natural no sul do Brasil

“…Com relação à eficiência de utilização do nitrogênio (EUN), a transformação deste insumo em produção primária se manteve praticamente constante, com valores de 6,1 e 7,1kg de MSV adicional (em relação ao tratamento Zero N) para cada kg de N aplicado, nas doses de 100 e 200kg ha -1 de N, respectivamente. Este resultado demonstra que a maior dose testada (200kg ha -1 de N) ainda está aquém da capacidade de resposta deste tipo de pastagem com fertilização nitrogenada, pois com o aumento do rendimento de matéria seca para cada unidade de nutriente disponível, a EUN decresce à medida que o rendimento se aproxima do potencial máximo de produção da planta (MAZZANTI et al, 1994;WHITEHEAD, 1995). AYALA & CARÁMBULA (1994) relatam valores de EUN para o inverno e verão de 1,5 e 14kg de MS kg -1 de N aplicado, respectivamente.…”