Tropentag, September 17 - 19, 2014 in Prague, Czech Republic "Bridging the gap between increasing knowledge and decreasing resources"

Optimising Ensilability of Sorghum-Soybean Mixture Using Epiphytic Lactic Acid Bacteria Inocula

¹La Salle University, Fac. of Agricultural Sciences, Colombia
²Intern. Center for Tropical Agriculture (CIAT), Tropical Forages Program, Colombia

Abstract

Lactic acid fermentation is a desirable trait for silage making. However, legumes own a high buffer capacity, which might lead to pitfalls when ensiling. In contrast, graminaceous forages may favour ensilability. The objective was to investigate the optimal sorghum/soybean proportion to optimise acidification. Secondly, we assessed epiphytic lactic acid bacteria (LAB) of sorghum (Sorghum bicolor L. var. H70) and soybean (Glycine max var. Panorama 29) to facilitate lactic acid fermentation in a rapid in vitro test (Rostock Fermentation Test-RFT). Forage was harvested at pre-flowering stage in December 2013 at CIAT Palmira, Colombia. LAB from sorghum and soybean were cultivated on Rogosa agar for 5 days at 35 °C and a single LAB from each material were isolated. Inoculates were evaluated for their acidification ability: LAB-epiphytic S738 (from sorghum), LAB-epiphytic S739 (from soybean), LAB from CIAT bacteria collection (S66.7), commercial silage inoculant (SilAll4×4™-Brazil) and a control. Sorghum and soybean and their combination (100/0, 33/67, 67/33, 0/100) were also tested for ensilability. 50 g of minced forage were introduced into an autoclaved 200 ml water in triplicate. The treatments were incubated at 37°C to determine the pH at 0 (before inoculation), 20, 28, 44 and 48 hours. We used a completely randomised design with factorial arrangement, where the first factor was the inclusion level of sorghum in the mixture and the second factor was the inoculant used. Yij=µ+Si+Ij+SixIij+eij; where Y= is the target variable, µ= is the overall mean, S= proportion of sorghum in the silage (100/0, 33/67, 67/33, 0/100)i, I= inoculant (S738, S739, S66.7 and control)j and e= random experimental error. At higher amounts of sorghum in the mixture, the pH registered lower averages. e.g. at 20h sorghum/soybean (100/0) the pH was 3.8, followed by 4.4 and 5.4 for sorghum/soybean mixture (63/37 and 37/63, respectively). The worst pH value (6.1) was for soybean alone (0/100). S738 (4.85) and S66.7 (4.86) showed the best acidifying potential at 20 hours (P=0.0196), whereas control had the worst pH value (5.05). Larger inclusion of sorghum assured better lactic acid fermentation. Epiphytic lactic acid bacteria are a feasible option to be used as inoculants to promote lactic acid fermentation.

Keywords: Epiphytic lactic acid bateria, rostock fermentation test, tropical forage

Contact Address: Mario Cuchillo Hilario, Intern. Center for Tropical Agriculture (CIAT), Tropical Forages Program, Recta Cali-Palmira km. 17, A.A. 6713 Cali, Colombia, e-mail: m.cuchillocgiar.org