Fotossíntese e taxa diária de produção de forragem em pastagens de capim-tanzânia sob lotação intermitente

Abstract

Resumo -O objetivo deste trabalho foi avaliar o efeito da intensidade de pastejo na taxa diária de acúmulo de forragem e na fotossíntese foliar líquida do capim-tanzânia, em pastagens manejadas sob lotação intermitente. O experimento foi conduzido de novembro de 1999 a outubro de 2000, em delineamento de blocos ao acaso, com quatro repetições. Os tratamentos experimentais foram três quantidades de massa de forragem verde remanescente (1.000, 2.500 e 4.000 kg ha -1 ), aplicados em ciclos de pastejo de 36 dias (33 de descanso e 3 de ocupação). A taxa diária de acúmulo de forragem não sofreu efeito da intensidade de pastejo e, com exceção no inverno, foi mais elevada nos primeiros 11 dias da rebrotação e nos períodos com temperaturas mais elevadas. A fotossíntese foliar líquida também não sofreu efeito da intensidade de pastejo (média de 23,2 µmol m -2 s -1de CO 2 ) e aumentou no decorrer da rebrotação, com os maiores valores entre o 11 o e o 22 o dias de rebrotação, nas diferentes épocas do ano. A fotossíntese foliar líquida variou com as alterações ocorridas na estrutura do dossel, durante o desenvolvimento das folhas. A utilização de períodos de descanso fi xos impediu que houvesse alterações na taxa de acúmulo de forragem causadas pela intensidade de pastejo.Termos para indexação: Panicum maximum, altura do dossel, estrutura do dossel, índice de área foliar, massa de forragem. Photosynthesis and daily forage productivity of Tanzania guinea grass pastures under rotational stockingAbstract -The objective of this study was to evaluate the effects of grazing intensity on forage accumulation rate and on net leaf photosynthesis of Tanzania guinea grass (Panicum maximum Jacq.) pastures under rotational stocking. The experiment was carried out from November 1999 to October 2000, in a randomized complete block experimental design, with four replications. Treatments were three levels of residual green forage biomass (1,000, 2,500, and 4,000 kg ha -1 ) in grazing cycles of 36 days (33 days of rest and 3 days of grazing). Forage accumulation rate was not affected by grazing intensities, and it was highest in the fi rst 11 days of regrowth during the periods of the highest temperatures. Net leaf photosynthesis was not affected by grazing intensity (mean 23.2 µmol m -2 s -1 CO 2 ) and increased during regrowth with the highest values between the 11 th and the 22 nd days of rest, depending on the season of the year. Net leaf photosynthesis was correlated with sward structure changes, during leaf development. The use of fi xed rest periods avoided alterations of forage accumulation rate caused by grazing intensity.

Biomass components of Pennisetum purpureum cv. Roxo managed at different growth ages and seasons

“…Anim., Salvador, v.19, n.1, p.11-22 jan./mar., 2018 ISSN 1519 9940 http://dx.doi.org/10.1590/S1519-99402018000100002 Perazzo et al (2013) observed higher biomass production in Sorghum genotypes of larger size. In the present study, there was a good positive correlation between height and GFB (r = 0.98, p<0.0001) and height and GSB (r = 0.96, p<0.0001), indicating a relevant contribution of the increase in stem with the increase in height of the plant, reaffirming the positive correlation between pseudo stem height and canopy height (CASTAGNARA et al, 2011) Possibly the highest LAI values in the rainy season intensified mutual shading, which triggered the stem elongation process (DAVIS & SIMMONS, 1994). This was confirmed by a negative correlation (r = -0.75, p<0.0001) between the LB/S ratio and GSB.…”

“…The GLB responded increasingly with advancement of the plant's age ( Table 2). The highest daily increase estimated as 98.15 kg ha -1 in the rainy season compared to the other seasons, was due to the better rainfall distribution, along with the availability of nitrogen, which has great relevance to the morphogenic rates, as documented in the literature (LOPES et al, 2011;CANTO et al, 2013). Araújo et al (2010) observed a decline in the photosynthetic rate from the fifth day of water deficit in Pennisetum purpureum cv.…”

“…The LAI presented a linear positive response with the increase in growth age in the three evaluated seasons (Table 3). The rest period fixed at 63 days allowed a continuous increase in leaf area, which probably led to an increase in the coefficient of light extinction and mutual shading; this may have compromised the distribution of active photosynthetic radiation (APR) and photosynthesis of the lower leaves (BRAGA et al, 2009), up to a climax moment. From this point, there was a significant increase in the senescence of shaded stems and leaf blades, which was demonstrated by a significant correlation between LAI and DFB (r = 0.85, p<0.0001), revealing the negative effects of postponing the harvest.…”

Biomass flow in Tifton-85 bermudagrass canopy subjected to different management strategies under rotational grazing with dairy goats

“…Even with a shorter residual height, the rLAI was possibly minimally adjusted to ensure high photosynthesis of remnant leaves and even those at the lower part of the canopy, providing large fixation of carbohydrates and favoring leaf elongation. In the light management, the pasture residual height may have been the greatest cause of diminished photosynthesis of remaining leaves on the canopy base affecting regrowth (Gomide et al, 2002;Braga et al, 2009). …”

Estimativa da assimilação potencial de carbono em dosséis de espécies de braquiária

“…Segundo Braga et al (2009), quando se deseja relacionar a produção de forragem com o processo fotossintético, outros fatores, como a partição dos fotoassimilados, devem ser cuidadosamente estudados. A assimilação bruta de carbono não se transforma necessariamente em produção colhível e tem baixa correlação com o AF (r = 0,23).…”