Morfogênese, produção, composição bromatológica e demanda hídrica do capim-tanzânia em tabuleiros costeiros do Piauí.

Abstract

Knowledge of the dynamics development of forage plants is an importam tool both for characterizing the potential production of a given species, as for the definition of potential use in a given ecosystem in animal production. One of the great challenges in the management of grassland has been to establish the most efficient practices in order to achieve the best sustainable yield of such ecosystems. The Tanzânia grass has been selected among the most promising fodder for establishment and / or pasture recovery, given their high biomass production, high acceptability, chemical composition and digestibility satisfactory. The objective of the work was to determine and evaluate the interrelationship between morphogenic, production and qualitative variables of Tanzânia grass with their actual water consumption over 35 days of growth, under the ecological conditions of the Coastal Tablelands of Piaui. The study was carried out in UEP-Parnaiba, Embrapa Mid-North, in two experimental periods, during the years 2008 and 2009. Regarding the determination of the morphogenesis, production and chemical variables, the experimental design was a randomized complete block with five replications, with treatments consisting of five regrowth ages (7, 14, 21, 28 and 35 days). In both experimental periods, the variables were tested at five ages of regrowth, with the sampling started after three subsequent cuts of uniformity, 10 cm above soil, in every 35 days. In evaluating the water consumption of the grass were used two weighing lysimeters, measuring 1.5 m x 1.5 m wide and long and 1.0 m depth to determine the crop evapotranspiration. The sprinkler irrigation was performed with a flow rate 3 1 of 0.630 m h~ and sprinkler lines spaced at 12m x 12m. The reference evapotranspiration was estimated by the Penman-Monteith equation from the climatic data in an automatic weather station. The rates of leaf appearance and leaf elongation showed a quadratic effect (p <0.05), with maximum values achieved at 24 and 26 days of regrowth, respectively. The rate of senescence showed a more pronounced increase at about 25 days of regrowth. The maximum number of live leaves per tiller was reached at 22 days of regrowth. The dry matter yield increased proportionally with age of regrowth reached a value of 5.7 t ha" in 35 days. The light interception increased asymptotically as a function of the leaf area index, which tended to stabilize between values 4 and 5 and light interception of 95%, corresponding to the interval between 21 and 24 days of regrowth. The crude protein content showed an opposite behavior, decreasing linearly from 17.0 to 7.8% from 7 to 35 days. The neutral detergent fiber content also linearly, reaching the criticai limit of less than 60% from 24 to 28 d. xiii regrowth and the acid detergent fiber content, using a quadratic behavior estimated values close to 35% by the age of 28 days. The average maximum evapotranspiration of Tanzânia grass for two years was 7.75 mm day"1. Considering the cutting interval of 35 days, Kc values recommended for the first year of grass are: 0.5, 1 to 3 days after cutting, 0.7 (4-6 days after cutting), 1.0 (7-10 days after cutting), 1.2 (11-16 days after cutting), 1.4 (17-23 days after cutting), 1,3 (24-30 days after cutting) and 1.1 (31-35 days after cutting). From the second year, the values of Kc should be: 0.6 (1-3 days after cutting), 0.9 (4-6 days after cutting), 1.1 (7-10 days after cutting), 1,3 (11-16 days after cutting), 1.5 (17-23 days after cutting), 1,4 (24- 30 days after cutting) and 1.3 (31-35 days after cutting). The analysis of the variables involved allowed the observation of the range of 21 to 24 days as the period of concentrated physiological characteristics of the most important in the development of Tanzânia grass, with implications in defining the most appropriate time for the occurrence of cutting or grazing. However, if consider the behavior of the grass in terms of water consumption, can be defined the interval of 24 days as the maximum grazing interval, since it also coincides with the peak of their water consumption.