Produção de novilhas em pastagem de capim Mombaça sob diferentes níveis tecnológicos

Abstract

Studies on tropical forage crops submitted to intensive management, regarding the characteristics of plant growth dynamics with animal performance, are still few. The objective of this study was to evaluate the effects of technological levels on the performance of heifers in grazing, forage production and chemical composition, morphogenic characteristics and carbon stock in Megathyrsus maximus cv. Mombasa. The treatments consisted of three technological levels: Level I (without nitrogen fertilization, 43 kg of K2O and 50 kg of P2O5 ha-1 year-1 + continuous stocking), Level II (150 kg of nitrogen, 75 kg of K2O and 50 kg of P2O5 ha-1 year-1 + rotated stocking) and Level III (300 kg of nitrogen, 150 kg of K2O and 50 kg of P2O5 ha-1 year-1 + rotated stocking). The experimental design was completely randomized with measurements repeated in time. The experiment was carried out at the Federal University of Tocantins, from January to May 2018 (Year II) and from January to May 2019 (Year II). Nellore heifers, nine months old, with an average live weight of 220 kg (Year I) and 250 kg (Year II) were used to graze and evaluate animal performance. The dry mass of total forage and leaf blade were higher at technological levels II and III (p <0.05). There was an increase in the proportion of dry mass of dead material when the pasture was submitted to technological level I (p <0.05), values of 440.21 g kg-1 . The values of crude protein increased with the increase of the technological levels of the pasture, presenting 102.8 and 149.9 g kg-1 in Level I and III, respectively. Reduction of neutral detergent fiber (NDF) levels in technological levels II and III (p <0.05). There was no difference for the average daily gain (GMD) of the animals (p> 0.05), average mean of 0.7 kg animal-1 day 1 . The stocking rate and total weight gain per hectare were high at the highest technological levels (II and III) (p <0.05), 3.48 and 6.83 AU ha-1 (AU = Animal Unit corresponding to 450 kg live weight) and 398 and 795 kg ha-1 live weight, for levels I and III, respectively. The nutritional index of nitrogen was considered luxurious consumption (p <0.05) in pastures that received nitrogen fertilization (Technological level II and III). There was a significant difference (p <0.05) for the variables rate of elongation and leaf appearance, in which they experienced increases in the highest technological levels (II and III) in relation to level I, which was of low technological level. A higher rate of leaf senescence was observed at level I (p <0.05). There was no reduction in the phyllochron for levels II and III when compared to level I (p <0.05). The highest technological levels (II and III) increased the number of live leaves, the final length of the leaf blade and the tillers population density. In general, between the two highest technological levels (II and III), there was no significant difference for the evaluated morphogenic characteristics. The root dry matter was higher at technological levels II and III (p <0.05). The organic matter litter did not differ between the technological levels (p> 0.05), average of 4291.66 kg ha-1 . The levels of organic matter and carbon stock did not differ (p> 0.05) during the short evaluation period (2018 to 2019), however an increase tendency was observed at technological level III, in which the highest level of nitrogen fertilization was applied (300 kg ha-1 of N). There was interaction between technological level and depth for the variables organic matter, and carbon stock (p <0.05), observing lower values of these variables in the level III with a depth of 10-20 cm. The increase in technological levels based on the use of nitrogen fertilization in pasture associated with rotated stocking in Mombasa grass pasture increases the production of forage dry matter, improves the nutritive value of forage and increases animal productivity, additionally improves morphogenic attributes and the structure of the pasture. The increase in technological levels in a short period of time increases the root dry mass, however, it does not influence the organic matter and the carbon stock of the soil, although it shows evidence that in longer periods there may be an increase in the values of these variables in the pasture soil with Mombasa grass, so studies for longer periods are necessary to generate more accurate data when using these higher technological levels.