The changing plant and tiller populations of timothy and meadow fescue swards. I. Plant survival and the pattern of tillering

In recent years several studies have increased our understanding of the growth and development of perennial herbage grasses. In particular, the production, life-history and development of individual tillers of single plants of timothy (Phleum pratense) grown in pots have been described (Langer 1956, 1957). As these studies took no account of competition between plants in swards, the growth of pure swards of timothy and meadow fescue (Festuca pratensis) was analysed in the field, first under conditions of uninterrupted growth (Langer 1958) and then under several cutting regimes (Langer 1959; Lambert 1962). However, since these experiments involved destructive sampling of small random areas of sward, no information could be obtained on the effect of management on the life-history of tillers or on the effect of competition on plant numbers. To consolidate the knowledge gained from previous work and to elucidate the fate of the individual components of the sward, an experiment was designed in which the life-histories of all tillers which arose within small, permanent quadrats of pure timothy and meadow fescue swards were studied over a period of 3 years. In this way it was possible to study, qualitatively and quantitatively, the development of swards of these two species from the seedling stage, under two cutting treatments based on agricultural practice

Duração do período de descanso e crescimento do dossel de Panicum maximum cv. Mombaça sob lotação intermitente Duration of rest period and canopy growth of Panicum maximum cv. Mombaça under intermittent stocking

O crescimento do dossel do capim-Mombaça foi analisado sob lotação intermitente com três períodos de descanso (PD), tratamentos definidos em função do tempo necessário para a expansão de 2,5; 3,5 e 4,5 novas folhas por perfilho e período de pastejo de seis dias. A área experimental foi dividida em cinco ou seis piquetes por tratamento. Utilizaram-se cinco novilhos mestiços (holandês x zebu) por tratamento, como animais de prova, além de outros, como animais de equilíbrio, que foram adicionados, quando necessário, para garantir índice de área foliar (IAF) residual de 2,0, ao final do 6(0) dia de cada período de pastejo. O estudo constou de duas fases de crescimento: 1) após roçada de uniformização, no início da estação de pastejo e 2) após alguns ciclos de pastejo, sob efeito dos três PDs. Os piquetes receberam adubação em cobertura de N, P2O5 e K2O, na dose de 50; 12,5 e 50 kg/ha, no início dos crescimentos 1 e 2. A intervalo médio de seis dias, durante 45 dias, estimaram-se a intercepção da radiação fotossinteticamente ativa (RFA), o IAF e a massa seca de forragem verde (MSFV). Aos dados de MSFV e de área foliar foram ajustados polinômios de segundo grau em função da idade, a partir dos quais foram estimados os valores instantâneos de biomassa e IAF e, a partir destes, as taxas de crescimento relativo (TCR) e de assimilação líquida (TAL) e a razão de área foliar (RAF), para cada idade. A intercepção da RFA pelo dossel evoluiu assintoticamente, alcançando valores máximos entre 95 e 98%, enquanto os valores de IAF e MSFV experimentaram incrementos ainda na faixa de estabilidade da intercepção da RFA. Os valores de TCR, TAL e RAF exibiram evolução assintótica decrescente. A grande proporção de colmo do dossel, ao final do PD mais longo, favoreceu a TCR e a TAL.<br>The canopy growth of Mombaçagrass was assessed under intermittent stocking with three rest periods, characterized by the time required for the expansion of 2.5, 3.5, and 4.5 new leaf blades per tiller, after grazing periods of six days. The experimental area was divided into five or six paddocks per treatment. Five crossbreed (Holstein x Zebu) steers were randomly assigned to each treatment. Extra steers were also used to achieve residual leaf area index of about 2.0, by the end of each grazing period. Two Growth phases were considered: 1) after standardization cut at the beginning of the growing season, and 2) after some grazing cycles had taken place, under the effects of the experimental rest periods. The paddocks received broadcast fertilization of N, P2O5 and K2O (50, 12.5 and 50 kg/ha) in the beginning of the growth phases 1 and 2. Photo synthetically active radiation (PAR) interception, leaf area index (LAI) and green forage dry mass (GFDM) were assessed over 45 days of regrowth, at six day intervals. Second order polynomials were adjusted to GFDM and LAI data, as a function of canopy ages. From these equations, instantaneous values of GFDM and LAI were estimated, from which it was derived the instantaneous values of relative growth rate (RGR) and net assimilation rate (NAR), respectively for each canopy age. PAR interception by the canopy increased in an asymptotic manner, reaching critical values of 95 - 98%, while LAI and GFDM values increased in the stability range of PAR interception. The growth indices RGR, NAR and LAR showed decreasing asymptotic evolution. The great proportion of stem in end of the longest rest period favored the decrease in RGR and NAR values