Photochemical Efficiency of Panicum Maximum Cv. Massai Submitted to Irrigation Depths and Residual Pastures Heights in the State of Tocantins, Brazil.

Abstract

Low forage production in dry season is mainly related to low water availability and low temperatures. Tocantins state is located in the North of Brazil, and the main factor limiting production is the insufficient water availability for pasture production during part of the year, since the temperature does not reach the minimum basal temperature that limits tropical grass development. The experiment field was installed in an area with Massai guineagrass pasture (9º57’0,65” S, 48º13’27,18” W, 444 m asl), grazed by lambs. The treatments included 21 days grazing cycles (1-d grazing period and 20-d rest period) of Panicum maximum cv. Massai (Massai guineagrass) submitted to three irrigation depths (0, 50 and 100% of crop evapotranspiration) and two residual pasture heights (20 and 30 cm). To help us understand that if with the supply of N-urea and irrigation is possible to overcome the seasonal reduction on pasture production due drought was carried a physiological analysis using PAM fluorimeter FluorPen FP100 to determine the photochemical efficiency of Massai guineagrass, assuming that the quantum yield (Fv/Fm or Qy) can be placed as a measurement of plant stress (Lu & Zhang, 1999). The results indicated that Qy measured in the early rainy season was minor than the measured in the late rainy season, indicating a grass recovery. Before, treatments with irrigation provided a recovery compared to rainfed, which is evidenced by the increase in Qy. The irrigated treatments did not present difference in the Qy when compared with rainfed or among depths. Finally, Qy may be used effectivelly to monitor the physiological state of the Massai guinea grass.

References cited

Lu, C., & Zhang, J. (1999). Effects of water stress on photosystem II photochemistry and its thermostability in wheat plants. Journal of Experimental Botany, 50(336), 1199-1206.

Acknowledgements

Fazenda Serra Verde, Embrapa and CNPq.