Características fisiológicas, produtivas e estruturais do capim faixa-branca submetido a doses de potássio

Abstract

This study was carried out to examine physiological, productive, structural and chemical parameters of digit grass fertilized with different doses of K2O from September 2016 to August 2017. Five K2O doses were tested, namely, 0, 80, 320, 400 and 640 kg/ha. The experiment was set up as a completely randomized design with four replicates. The experimental area was irrigated throughout the experimental period. When the grass was fertilized with 640 kg/ha K2O, the “a”, “b” and total chlorophyll indices decreased by 16, 20 and 18%, respectively, compared to control. The highest initial and maximum fluorescence and maximum quantum yield means of photosystem II were observed with the application of 640 kg/ha K2O, revealing 123.7, 463.4 and 0.733 electrons/quantum, respectively. Basal, aerial and total tiller density and total, leaf and stem dry mass accumulations fitted a quadratic model, with maximum values of 535, 182 and 717 tillers/m² and 27,146, 15,311 and 11,222 kg/ha DM at the respective K2O, doses of 351, 308, 327, 502, 471 and 545 kg/ha. The percentage of stems rose linearly with the K2O doses. Percentage of dead mass, leaf/stem ratio, and the crude protein content of the leaves declined linearly as the K2O doses were increased. The percentage of leaves in digit grass was not influenced by the potassium doses, averaging 56.1% of the total accumulated herbage. Digit grass has the highest leaf dry mass accumulation potential and best chemical composition at the K2O dose of 470 kg/ha. High K2O doses negatively influence physiological parameters such as chlorophylls and the fluorescence of chlorophyll “a”.