Evaluation of the productive and nutritional potential of Lablab purpureus cv. Rongai

Héctor L. Santana de Armas
Estación Experimental de Pastos y Forrajes “Indio Hatuey” Central España Republicana 44280,Matanzas, Cuba

ABSTRACT
In order to determine the influence of the season, sowing moment, harvest age and phenological status on the yields, leaf percentage, bromatological composition and nutritional quality, in Lablab purpureus cv. Rongai, trials were conducted during four years, at the Pasture and Forage Research Station “Indio Hatuey”. The sowing was performed by seeds in doses of 20 kg/ha of pure germinable seed, using a basic fertilization of triple sodium phosphate and potassium chloride, 50:50 kg/ha. Fifteen days after the plants emerged, a nitrogen fertilization with urea was applied at a rate of 60 kg/ha. In the dry season irrigation was applied, 200-250 m3/ha, every 15-20 days. The forage was obtained from plots with variable dimensions (1 500-2 500 m2), according to the green mass requirements necessary for the evaluation with the animals. The dry matter yields and the composition of leaves and stems during the measurement periods were determined. In all the experiments, for the determination of the nutritional value, 6 adult, castrated male sheep were used, with live weights from 37 to 40 kg, confined in individual metabolism cages. The procedure used was total feces collection, with daily weighing of the offered forage and of the residues. The forage, before being offered, was chopped to 2 or 3 cm and supplied at will, guaranteeing 10 % more than the intake from the previous day. Representative 300-g samples of the forage and residues and 10 %, in weight, of the feces of each animal, were taken. The samples were dried for 48 hours, to determine the dry matter content and to have material for the later bromatological analyses. At the end of the measurement periods, the samples were homogenized to determine the ash, nitrogen and crude fiber content. The calculations of the digestibility of dry matter, organic matter, crude protein (N x 6,25), crude fiber and the intake based on the metabolic weight (P0,75) were individually made and the energy contents and the digestible nutrient intake were carried out according to the methods described by Cáceres et al. (2006). The differences among means were determined by Duncan’s multiple range comparison test, for a significance level of P < 0,05, using the statistical program SPSS, version 10.1 for Windows. The results indicate that the productive potential of Lablab purpureus cv. Rongai is influenced by the sowing moment and the season, that the best sowing moments are, in the rainy season, the months of May-June and in the dry season, the months of November-December, when it is possible to utilize all the phenophases of the crop. This legume can be used throughout the year because it maintains adequate and stable bromatological values and digestibilities. In the rainy season, when the plant is in vegetative state, the digestibility of the crude protein increases until the 77 days and in the dry season the highest values in the OMD are shown when it is in milky grain status and for the CFD, during flowering and pod formation. The DM intake is affected by the season, sowing moment, phenological status and leaf content, achieving the highest values when the plant is in the milky grain phenophase. The intake of the other nutrients, due to its links with the DM ingestion, follows the same performance. It is recommended to promote, through theoretical and practical training seminars, the promotion of seed production and the use of this plant as cut and carry legume to supplement ruminants, to perform studies for its introduction in the technologies of elaboration of mixed silages and hay, its utilization in the protein bank, alone or as companion legume of forage plants, as intercropped crop in short-cycle species and as soil ameliorator.