Generation of models from existing models composition: An application to agrarian sciences.

Mathematical models that describe gas production are widely used to estimate the rumen degradation digestibility and kinetics. The present study presents a method to generate models by combining existing models and to propose the von Bertalanffy-Gompertz two-compartment model based on this method. The proposed model was compared with the logistic two-compartment one to indicate which best describes the kinetic curve of gas production through the semi-automated in vitro technique from different pinto peanut cultivars. The data came from an experiment grown and harvested at the Far South Animal Sciences station (Essul) in Itabela, BA, Brazil and gas production was read at 2, 4, 6, 8, 10, 12, 14, 17, 20, 24, 28, 32, 48, 72, and 96 h after the start of the in vitro fermentation process. The parameters were estimated by the least squares method using the iterative Gauss-Newton process in the software R version 3.4.1. The best model to describe gas accumulation was based on the adjusted coefficient of determination, residual mean squares, mean absolute deviation, Akaike information criterion, and Bayesian information criterion. The von Bertalanffy-Gompertz two-compartment model had the best fit to describe the cumulative gas production over time according to the methodology and conditions of the present study.

Biomass turnover in brachiaria cultivars in a tropical environment / Fluxo de biomassa em cultivares de brachiaria em ambiente tropical

The experiment was conducted to evaluate the morphogenetic traits of three Brachiaria cultivars (common, Llanero and Tupi) subjected to continuous grazing with variable stocking rate in the four seasons of the year. A randomized block design with five replicates was adopted. Tissue turnover evaluations were carried out in the summer, fall, winter and spring, with measurements taken every two days. Stem length and the length of each green leaf were measured. With these determinations, the following variables were calculated: stem elongation rate (cm/tiller/day), leaf elongation rate (cm/leaf/day), number of live leaves per tiller and phyllochron (days/leaf). The highest leaf appearance rate was obtained by Tupi grass in the summer, and the lowest by Llanero grass in the winter. The lowest phyllochron, 5.90 days/leaf, was obtained by Tupi grass in the winter, whereas in commercial cultivars Llanero and common the average phyllochron was 9.04 and 10.04 days/leaf, respectively. Because of the effect of the transition from the dry season to the beginning of rains in the summer, this was the period of greatest variations in results among the different cultivars. Llanero grass stood out for the highest values for plant, tiller and leaf lengths, resulting from greater stem and leaf elongation rates. Tupi grass had the worst performance of all cultivars.

O experimento foi realizado com o objetivo de avaliar as características morfogenéticas de três cultivares de Brachiaria humidicola (common, Llanero e Tupi), submetido a pastejo contínuo, em quatro estações do ano. Foi utilizado delineamento em blocos casualizados, com cinco repetições. As avaliações do volume de tecido vegetal foram realizadas no verão, outono, inverno e primavera, e as medidas foram tomadas a cada dois dias. Determinaram-se o comprimento da haste e o comprimento de cada lâmina de folha verde. Com essas determinações, foram calculados: taxa de alongamento (cm / perfilho / dia), taxa de alongamento foliar (cm / folha / dia), número de folhas vivas por perfilho e filocromo (dia / folha). A maior taxa de aparecimento de folhas foi obtida na grama Tupi no período de verão, e o menor aparecimento ocorreu no cultivar Llanero, durante o inverno. O menor filocromo (5,90 dias / folha) foi verificado no cultivar Tupi, no inverno, enquanto no cultivares Llanero e common o filocromo médio foi de 9,04 e 10,04 dias / folha, respectivamente. Devido ao efeito da transição, a partir da estação seca para o início das chuvas no verão, foi constatado que as maiores variações nos resultados dos diferentes cultivares, ocorreram nesta época. O cultivar, Llanero se destacou para os maiores valores da planta, resultante das maiores taxas de alongamento de caule e folhas. O cultivar Tupi teve o menor desempenho em comparação com os outros.