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Forage accumulation and nutritive value of Convert HD 364 (Brachiaria hybrid) under contrasting growth rates in response to canopy height maintained by continuous stocking

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Author(s):
Ianê Correia de Lima Almeida
Total Authors: 1
Document type: Master's Dissertation
Press: Piracicaba.
Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
Defense date:
Examining board members:
Carlos Guilherme Silveira Pedreira; Valdo Rodrigues Herling; Patricia Menezes Santos
Advisor: Carlos Guilherme Silveira Pedreira
Abstract

Pastures occupy a large area in Brazil and are key to the country\'s livestock industry, which is almost exclusively forage-based. Grazing management, however, is largely empirical in the country, and technical guidelines for managing specific grasses are either scarce or poorly adopted, which hinders the competitiveness of the activity. Establishing sound management guidelines for key grasses can improve animal output and profitability of the livestock enterprise. The objective was to describe and explain differences in the productive potential and the qualitative traits of Convert HD 364 brachiariagrass through the characterization of agronomic and sward structural attributes as well as forage nutritive in response to three grazing intensities and under two growth rates under continuous stocking and variable stocking rate in a mob-grazing experimental protocol. The study was conducted in Piracicaba, in summer of 2013. Experimental paddocks received treatments corresponding to all possible combinations among three sward heights (10, 25, and 45 cm) and two growth rates generated by two N rates (50 and 250 kg N ha-1) split-applied monthly during the experimental period. The experimental design was a randomized complete block with a factorial arrangement. Response variables included forage accumulation and accumulation rate, LAI, plant-part composition of forage on offer, as well as plant-part composition and nutritive value (crude protein - CP, neutral detergent insoluble fiber - NDF digestibility in vitro organic matter - IVDMD) of forage. The highest values of forage accumulation and accumulation rate were recorded for swards kept at 40 cm (12650 kg DM ha-1 yr-1 and 110 kg ha-1 d-1, respectively) and for swards fertilized with 250 kg N ha-1 (13974 kg DM ha-1 yr-1 and 126 kg DM ha-1 day-1, respectively). This same combination resulted the highest LAI (8.1). Forage mass was affected by sward height but not by N rates being higher for 40-cm (14650 kg DM ha-1). Treatments with higher N (250 kg ha-1) resulted in forage with a higher proportion of leaf (26%). Higher percentages of stem (40%) were measured in swards grazed at 40 cm and fertilized with 50 kg N ha-1 while the proportion of dead material was higher (49%) in 10-cm swards receiving 50 kg N ha-1 of N. Swards kept at 10 cm and receiving 50 kg N ha-1, although less productive, resulted in forage with higher IVOMD (670 g kg-1). Forage in 10-cm swards had 153 g kg-1 crude protein and that from swards receiving 250 kg N ha-1 had 165 g kg-1. Neutral detergent fiber concentration was higher in forage from 40-cm swards (545 g kg-1) and from those receiving 50 kg N ha-1 (550 g kg-1), which is also associated with the maturity of the tissues at the time of harvest. Nitrogen fertilization promotes gains in productivity and results in forage with better nutritive value, whereas increases in canopy height promote higher total accumulation and rate of herbage accumulation, up to 25 cm. The treatment that combines high productivity with high nutritive value is 25 cm canopy height and 250 kg ha-1. (AU)