Key factors that influence for seasonal production of Guinea grass

Climate, soil and management are the main drives for growth and production of tropical pastures. Thus, a better understanding of the effects of these factors and their interactions under climate conditions is required to obtain effective management options. Here, we used data from two field trials to research on climate and management interactions on the production seasonality of Panicum maximum Jacq. Treatments included four sampling times (250, 500, 750, and 1000 °C accumulated) during eight regrowth period, under irrigated and rainfed conditions and, cuts were made to simulate grazing intensity. All treatments were arranged in a completely randomized block design with four replications. At each sampling time, basal tillers were sampled to observe meristematic differentiation and were linked with the respective daylength. Soil moisture was determined, and the water availability index (WAI) was calculated. The dry matter production (DMP) was taken and relative productivity was calculated. Soil moisture was the key seasonal drive in spring-summer and the WAI could be used to adjust the maximum production for that season. The major drive for DMP in fall was the daylength, which was found at 11.81 h. For all seasons, DMP correlated better with the residues in early regrowth phase (r = 0.82 and p < 0.0001) and with degree-days at final regrowth phase (r = 0.73 p < 0.01). Applying these critical values to management guidelines should make Guinea grass DMP more efficient on tropical farms.

Key factors that influence for seasonal production of Guinea grass

Climate, soil and management are the main drives for growth and production of tropical pastures. Thus, a better understanding of the effects of these factors and their interactions under climate conditions is required to obtain effective management options. Here, we used data from two field trials to research on climate and management interactions on the production seasonality of Panicum maximum Jacq. Treatments included four sampling times (250, 500, 750, and 1000 °C accumulated) during eight regrowth period, under irrigated and rainfed conditions and, cuts were made to simulate grazing intensity. All treatments were arranged in a completely randomized block design with four replications. At each sampling time, basal tillers were sampled to observe meristematic differentiation and were linked with the respective daylength. Soil moisture was determined, and the water availability index (WAI) was calculated. The dry matter production (DMP) was taken and relative productivity was calculated. Soil moisture was the key seasonal drive in spring-summer and the WAI could be used to adjust the maximum production for that season. The major drive for DMP in fall was the daylength, which was found at 11.81 h. For all seasons, DMP correlated better with the residues in early regrowth phase (r = 0.82 and p < 0.0001) and with degree-days at final regrowth phase (r = 0.73 p < 0.01). Applying these critical values to management guidelines should make Guinea grass DMP more efficient on tropical farms.(AU)

Estresse por deficiência hídrica em genótipos de Brachiaria brizantha / Hydric deficiency in genotypes of Brachiaria brizantha

O experimento foi desenvolvido em casa de vegetação na Embrapa Pecuária Sudeste, utilizando acessos de Brachiaria brizantha. O delineamento experimental foi o de blocos ao acaso, com arranjo fatorial 2 X 4, sendo dois tratamentos (com e sem déficit hídrico) e quatro genótipos. O grupo de genótipos avaliado foi formado pelas cultivares 'BRS Piatã', 'Marandú', 'Xaraés' e 'BRS Paiaguás', sendo o experimento realizado durante o mês de julho de 2008. As variáveis analisadas foram massa seca total, massa seca de parte aérea, massa seca de raiz, massa seca de colmo, massa seca de folha, taxa de alongamento foliar, área foliar, área foliar específica. O estresse por deficiência hídrica exerceu efeito negativo em todas as características estudadas e em todos os acessos avaliados. A cultivar 'BRS Piatã' foi o genótipo que menos apresentou alteração entre os tratamentos com e sem déficit hídrico, indicando portanto, tolerância dessa cultivar em relação ao estresse por falta de água no solo nessas condições experimentais.(AU)

The experiment was conducted in a greenhouse at Embrapa Southeast Livestock, using Brachiaria brizantha accessions. The experimental design was fully randomized blocks with a 2 x 4 factorial arrangement, with two treatments (with and without water deficit) and four genotypes. The group evaluated was formed by genotypes 'BRS Piatã', 'Marandu', 'Xaraés' and 'BRS Paiaguás'. The experiment was conducted during the month of July 2008. The variables analyzed were dry mass of total plant, shoot mass, leaves, stems and roots, leaf elongation rate, leaf area and specific leaf area. The water deficit stress exerted negative effect on all characteristics studied and in all accessions. 'BRS Piatã' was the genotype that showed less change between treatments with and without water deficit, thus indicating tolerance of this cultivar in relation to water stress in the soil under these experimental conditions.(AU)