Aspectos morfofisiológicos de espécies forrageiras da caatinga sob adubação fosfatada e pastejo

Abstract

Livestock production in the semiarid region of Brazil is important for income generation and survival of the peasant. However, in most cases, it is developed extensively. The objective was to study the effects of phosphate fertilizers and fodder supply on morphophysiological aspects of plant Mororó [Bauhinia cheilantha (Bong.) Steud.] And Feijão-bravo [Cynophalla flexuosa (L.) J. Presl] manipulated in Caatinga. The survey was conducted at the Academic Unit of Serra Talhada, Federal Rural University of Pernambuco, a Caatinga area enriched with Mororó, capim-corrente [Urochloa mosambicensis (Hack.) Daudy] and Buffel grass (Cenchrus ciliaris L.). Two experiments were conducted over a year, from 2014 to 2015. In the first experiment, the effects of P fertilization (0, 50 and 100 kg P2O5/ha/year) on morphological characteristics (specific leaf area, area, length , sheet width and perimeter, plant height, crown diameter, stem diameter, structural features and phenological) and physiological (gas exchange, SPAD index, relative water content, membrane damage). The treatments were randomized into three experimental blocks with four replications in each block. Feijão-bravo plants were characterized by higher number of leaves (12.0) and higher dry weight of leaves (514.0 mg) along the evaluations when not fertilized with phosphorus. The Feijão-bravo showed no light saturation to the level of 1600 micromol photons/m²/s. We obtained higher net CO2 assimilation values greater was applied to the fertilizer level (7.6 micromol CO2/m²/s). The most suitable conditions Mororó sheets relative to higher relative water content (64%) and less damage of membrane (30%) were obtained in the rainy season. For Mororó, the higher specific leaf area (275.7 cm²/g) was obtained in April with the treatment of 50 kg P2O5/ha/year. The sheets had Mororó light saturation level of photosynthetically active radiation around 500 micromol photons/m²/s. They were obtained higher net assimilation rates of CO2 (2.12 micromol CO2/m²/s) and the lower the level of fertilizer applied. In the second experiment we studied the effect of four forage allowance (2.0, 2.5, 3.0 and 3.5 kg DM/kg BW) on the same characteristics described above. The grazing method was continuous stocking with variable stocking rate and duration of the two-month grazing season. The treatments were randomized experimental block design with three replications. Wider Feijão-bravo sheets (5.40 cm), of larger size (7.38 cm) and greater dry weight (584.0 mg) were observed in forage allowance between 2.5 and 3.0 kg DM/kg BW. Wider Mororó sheets (7.62 cm), of larger size (7.09 cm) and larger area (44.77 cm²) were observed after the grazing season. The number of leaves per secondary branch in Mororó plants decreases after the grazing period, occurring the total loss of leaves in October 2014. The number of main branches in plant Mororó was lower (3.0) on offer between 2.5 and 3.0 kg DM/kg BW in the months that have carried out grazing season (August and October 2014). The application of phosphate fertilizer contributed to the Feijão-bravo plants had larger amount of leaves in a shorter time. For Mororó the lowest phosphorus added level resulted in higher investment in the plant in producing thicker sheets. The forage allowance did not affect the physiological traits both in Feijão-bravo as the Mororó.