Levantamento dos elementos minerais em plantas forrageiras de áreas delimitadas do estado de São Paulo. IV — zinco

Abstract

The present experiment was undertaken to compare zinc concentrations in the tops of the pasture plants — Coloniao (Panicum maximum), Jaragua [Hyparrhenia rufa (Nees) Stapfj and Gordura (Melinis minutiflora) — three of the main forage species grown on restrict areas at the hinterland of Sao Paulo State, Brazil. The samples were collected according with four types of soil, in dry and wet seasons in July and January, respectively, in order to find out the concentrations of this element. An analysis of the variance of zinc contents in the whole tops showed that the three grasses differed no significantly but there were significant differences between dry season (65 p.p.m.) and damp season (40 p.p.m.). As the seeds have a high amount of zinc, it seems that this fact has had the greatest influence in determining these wide differences between seasons, once the pasture plants presented different stages of development of their seeds at the harvest. The mean zinc concentrations in dry season — 60 p.p.m. (Panicum maximum), 69 p.p.m. Hyparrhenia rufa (Nees) Stapf] and 66 p.p.m. (Melinis minutiflora) — and in wet season — 37 p.p.m. (Panicum maximum), 36 p.p.m. [Hyparrhenia rufa (Nees) Stapf] and finally, 48 p.p.m. (Melinis minutiflora) — emphasized the very low variation in zinc levels among grass species. The very important role of this element in forage pastures and its relationships with calcium, copper, molybdenum and other dietetic factors, in order to avoid a nutritional disease in cattle, sheep and also in swine were discussed and the necessity to supply this micronutrient in mineral mixture, due to the reduced amounts encountered in the pasture plants was accentuated.