Decomposição e composição química de liteira de Brachiaria decumbens Stape e Colopogonium mucunoides Desv.

Abstract

This study aimed to compare the litter decomposition of two forage species, a grass (Brachiaria decumbens Stapf.) and a legume (Calopogonium mucunoides Desv.),in two different environments (field vs. rumen). Two incubation trials were carried out.In the first study, litter decomposition was evaluated using the nylon bag technique under field conditions at the “Itambé” Experimental Station from the Agronomic Institute of Pernambuco (IPA). The second study was performed by incubating the litter of the two species in the rumen of fistulated goats, using the in situ degradability technique and it was developed at the Animal Science Department of the Federal Rural University of Pernambuco (UFRPE). This second trial was carried out aiming to compare decomposition processes in the rumen vs. in the field. Decomposition was studied by incubating the senescent material of Brachiaria decumbens and Calopogonium mucunoides in eight different periods for the field trial (0, 4, 8, 16, 32,64, 128 and 256 days) and in six different periods for the goat trial (0, 6, 12, 24, 48, 96 and 144 hours). The tratament was incubated in three different proportions (100% Brachiaria decumbens, 100% Calopogonium mucunoides, and 50% Brachiaria decumbens + 50% Calopogonium mucunoides)and complete randomized block designwas used with five replications for the field. For the goats, the same experimental design was used, but with three replications per treatment. For the field experiment, the values of the relative decomposition rate (k) were significant (P <0.0014) for different treatments (kcalop. = 0.0056 g.g-1.day-1, kB + C =0.0045 g.g-1.day-1 and kBrac = 0, 0037 g.g-1.day-1). Inclusion of Calopogonium mucunoides had a positive linear effect (P <0.0014) on k, reducing the percentage ofremaining biomass at the end of the incubation period (P <0.0001). Highest C:N ratio values were found for Brachiaria decumbens (~ 95), followed by the mixture of the two species (~ 32), and finally by Calopogonuim mucunoides (~ 20 ). Lignin concentration was different between treatments (P<0.0001), increasing during the incubation,stabilizing at 21%. In the comparative experiment (field vs. Rumen), the percentage of remaining biomass for Brachiaria decumbens at the end of the incubation period was similar both for the rumen and for the field (~ 38%). Calopogonium mucunoides presented lesser remaining biomass in the rumen than in the field by the end of the incubation period. The percentage of N remaining in the rumen was lower than in the field for both tested species at the end of incubation time. The C:N was considered high for B. decumbens both for the rumen (105) and for the field (95). The inclusion of Calopogonium mucunoides in pastures of Brachiaria decumbens accelerates the litter decomposition having potential to accelerate the recycling of nutrients in these ecosystems. In a general way, the rumen environment promoted greater N disappearance; however, the final remaining biomass was similar for decomposition inboth environments, specially for Brachiaria litter, showing likely similar limits for decomposition in both environments.