Leguminosas forrageiras em pastos consorciados: métodos para mensurar a composição botânica da dieta e diversidade e eficiência de bactérias fixadoras de nitrogênio em amendoim forrageiro

Abstract

ARTICLE 1: The objective was to develop and adapt techniques capable of estimating the intake and proportion of grasses and legumes in the diet of cattle with faecal analysis using NIRS and abundance of carbon 13. Two experiments were carried out with Tabapuã heifers confined and arranged in square latin 4 x 4, with four diets and four heifers, in each experiment. In the first experiment, the diets were the following: 100% Brachiaria brizantha (cv. Marandu); 66.7% B. brizantha + 33.3% Arachis pintoi (Belomonte cv); 33.3% B. brizantha + 66.7% A. pintoi; and 100% A. pintoi. In the other experiment, the diets were: 100% Cynodon dactylon (cv. Coast-cross); 66.7% C. dactylon + 33.3% Medicago sativa (cv. Crioula); 33.3% C. dactylon + 66.7% M. sativa; and 100% M. sativa. The experimental period was 15 days, being 10 days of adaptation to diet and 5 days of collection. The diet was offered twice a day (8 and 17 h), and the leftovers collected daily. In order to obtain the indigestible fibers, the hays and feces were incubated and treated with neutral detergent solution (FDNi) or acid (FDAi). 13C isotopic abundance was determined in the ground dry faeces (FSM), FDNi and FDAi of faeces. The dry matter intake (CMS) and the botanical composition of the diet were estimated through FDNi and FDAi in the feces and by the in vitro dry matter digestion (DIVMS) of the hays. The comparisons between the observed and estimated values of the botanical composition were performed in the function of the mean square of the prediction error (QMEP) and the partition of the sources of variation of the QMEP. For analyzes of the NIR spectrum, only one FDNi and FDAi of feces were evaluated. After the treatment of the spectra, main component analyzes (PCA), calibration of models, complete cross validation (leave one out) and external validation (test set) were performed. Identity models were used (Y = β0 + β1.x, with the following joint hypotheses: H0: β0 = 0 and H0: β1 = 1) for validation of the models. Analyzes were performed using the SAS® REG procedure. The FDNi and FDAi of the ingested diet was not different from that excreted in the faeces. The total CMS observed did not differ from that estimated using the techniques of FDNi, FDAi and DIVMS of grass and legume hay. As a function of QMEP, as indigestible fibers presented better estimates compared to DIVMS to predictingthe botanical composition in grass and legume diets. The mathematical model of smoothing in the NIR spectra in the FDNi of the feces of diets with Brachiaria and forage peanut, and autoscale in the NIR spectrum in the FDNi of the feces of Coast-cross and alfalfa diets were capable of predicting the proportion of grasses and legumes in the feces. It can be concluded that by analyzing the 13C isotope in the FDNi of the feces, it is possible to estimate the botanical composition of the diet ingested in pastures intercropped between grasses and legumes. The NIR spectrum is able to predict the efficiency of the botanical composition of cattle faeces. *************** ARTICLE 2: The use of grasses mixed with forage peanut (Arachis pintoi) in pastures is growing and promising, because this forage legume has a stoloniferous habit of growth and tolerates greater defoliation intensities. However, few studies are available on its symbiosis with N2-fixing bacteria. The objective of this study was to evaluate the phenotypic and genetic diversity, and efficiencyof strains of bacteria isolated from Arachis pintoi nodules established in grassland areas. Root nodules of the forage legume A. pintoi, cultivars Mandobi and Belomonte were collected in Itabela-BA and Lavras-MG. Collection areas had contrasting physical and chemical characteristics. Ten plants were sampled collecting five nodules per plant. Subsequently, the nodules were hydrated for 30 min in sterilized distilled water, followed by superficial disinfestation for 30 s in alcohol, 3 min in H2O2 (10%) and washed six times in sterile distilled water. The nodules were macerated plates containing the medium79 and incubated at 28 ° C until the colonies appeared. The colonies were harvested until obtaining pure culture. Analysis of the cultural characteristics (growth time and pH change of the culture medium) of the strains, partial sequencing of the 16S rRNA gene and evaluation of the symbiotic capacity in plants of A. pintoi were performed. The symbiotic capacity was evaluated in a greenhouse experiment with long neck bottles (500 mL), filled with nutrient solution, under axenic conditions, in a completely randomized design with four replications. An evaluation of the symbiotic efficiency of strains in A. pintoi cv. Mandobi in polypropylene tubes containing a mixture of sand and vermiculite. The results of each experiment were submitted to normality test and analysis of variance using SISVAR software. The means of the treatments were grouped by the Scott-Knott test, at 5% probability. Seventy-six bacterial strains were obtained from the isolation of forage peanut nodules, 40 from Itabela-BA and 36 from Lavras-MG. In the experiment with the Itabela-BA strains, 17 presented nodulation and, in the experiment with the Lavras-MG strains, 14. Partial sequencing of the 16S rRNA gene was obtained for 50 strains, 31 from Bahia and 19 from Minas Gerais. The strains of forage peanut nodules from pasture areas of Itabela-BA were identified in the following genera: Bradyrhizobium (22), Rhizobium (5), Burkholderia (2), Kocuria (1) and Paenibacillus (1). The strains from Lavras-MG soils were identified in the genus Bradyrhizobium (13), Rhizobium (2), Burkholderia (2), Mucilaginibacter (1) and Enterobacter (1). Twenty - four native strains with nodulation capacity were identified in forage peanuts. Strains 05-153, 05-163, 05-98 and 05-133 were promising and with the potential to carry out a more efficient symbiosis process between the plant and the bacteria. The forage peanut is able to nodulate only in symbiosis with some strains of the genus Bradyrhizobium and some isolated native strains were more efficient at nodulating the forage peanut than the strains currently approved as inoculant.