Decline in plant and animal production from ageing pastures of green panic (Panicum maximum var. trichoglume)

Abstract

The impact of age on the productivity of sown pastures of green panic (Panicum maximum var. trichoglume cv. Petrie) growing on black earth soil in south-east Queensland was measured from 1976 to 1981. During winter and spring, weaner steers grazed at 2-4 animals/ha on summer-spelled pastures which, in each year, were 1, 2, 3, 4 and 5 years old. Pastures were given 58 kg N/ha as urea each year. Live-weight gain averaged 74 kg/head on 1-year-old pasture but only 35 kg/head on 5-year-old pasture, with most of the reduction in weight gain in winter (June to August) occurring up to age 3 years, and with most of the reduction in spring (September to November) occurring for pastures older than 3 years.The decline in animal production was not caused by changes in species composition of the pasture. Rather, weight gain on older pastures was restricted by pasture quality in winter and by reduced pasture growth in spring, but not by presentation dry-matter yield. The decrease in pasture productivity seemed to be primarily due to reductions in available soil mineral N with age, since the N concentration of plant shoots decreased as a pasture aged. Tt is postulated that the immobilization of N in decomposing grass litter is a primary cause of productivity decline in ageing pastures.

Yield and nutritive value of the spring growth of an ageing timothy sward

“…A reduction in herbage productivity with ageing swards has been reported for other temperate (Smith and Allcock 1985;Loiseau et al 1992) and tropical grass species (Robbins et al 1987). In our study, the yield decline of the spring growth with ageing timothy swards ranged from 0.47 to 0.91 Mg DM ha…”

“…It has been suggested that the increasing presence of plant litter with ageing swards can result in N immobilization, then causing a N deficiency (Robbins et al 1987;Loiseau et al 1992). In our study, relatively high N fertilizer rates were applied and it was found, based on an analysis of relative yields, that maximum DM yields were reached in all years of the study.…”

“…Les taux de changement de la valeur nutritive observe´s au cours du de´veloppement de la croissance printanie`re e´taient donc plus rapides dans les vielles plutoˆt que les jeunes prairies. Nos re´sultats de´montrent bien la baisse de productivite´avec l'aˆge de la fle´ole des pre´s et ses conse´quences sur sa valeur nutritive.Mots clé s: Phleum pratense, anne´e de la re´colte, stade de de´veloppement, rendement, digestibiliteT he decline in productivity of forage grasses with age since establishment has been recognised for several years, both in temperate (Garwood et al 1977, cited by Robbins et al 1987Smith and Allcock 1985;Loiseau et al 1992) and tropical (Robbins et al 1987) grasses. There is, however, very little information on the decline in productivity in ageing swards of timothy (Phleum pratense L.).…”

“…Mots clé s: Phleum pratense, anne´e de la re´colte, stade de de´veloppement, rendement, digestibiliteT he decline in productivity of forage grasses with age since establishment has been recognised for several years, both in temperate (Garwood et al 1977, cited by Robbins et al 1987;Smith and Allcock 1985;Loiseau et al 1992) and tropical (Robbins et al 1987) grasses. There is, however, very little information on the decline in productivity in ageing swards of timothy (Phleum ranging from 0.019 to 0.43 Mg DM ha…”

Dinâmica de decomposição e mineralização de nitrogênio em função da qualidade de resíduos de gramíneas e leguminosas forrageiras

“…Isto compromete a sustentabilidade da produção das gramí-neas forrageiras e, conseqüentemente, a produtividade animal (Robbins et al, 1987;Corsi & Martha Jr., 1997).…”