Fermentability of corn-lablab bean mixtures from different planting densities

This study was conducted to determine silage fiber characteristics and fermentation profiles of corn (Zea mays L.) grown in mixture with lablab bean [Lablab purpureus (L.) Sweet] at different planting densities. The experiment was conducted in two environments in 2005. 'Rongai' lablab bean and corn were intercropped at eight different planting densities; 20/80, 40/0, 40/40, 40/80, 60/0, 60/40, 60/80, and 80/80 thousand corn/lablab bean plants/ha. Corn in monoculture or in mixture with bean was harvested between 1/2 and 3/4 milk line. Two 1-L glass jar mini-silos per treatment per replicate plot were filled at a density of 500g/L, eight jars per treatment per location, and stored for 40 days at room temperature (~22°C). At the time of ensiling a 500-g fresh sub-sample was also taken for dry matter (DM) and initial characterization of the corn and corn-bean mixtures. Each silo was analyzed for fiber characteristics, pH, and fermentation products. Silage crude protein (CP) concentration was on average 17.5% (86.4g/kg DM) greater in the mixture than monoculture corn (73.5g/kg DM). The in vitro true digestible DM (IVTDDM) concentrations in the mixtures were on average 4.6% less (796g/kg DM) than that of monoculture corn (834g/kg DM), but neutral detergent fiber digestibility was not different between monoculture corn and corn-lablab mixtures (P>0.05). Lactate concentration was 21.2% higher in the corn-lablab bean mixtures (60.5g/kg DM) than monoculture corn (49.9g/kg DM). The contribution of the lablab bean to the mixture increased as corn planting density decreased. Thus the maximum benefits to increased CP occurred in the mixtures with the lowest corn planting densities, but those mixtures also had the greatest reductions in IVTDDM. However all treatments fermented well in spite of significant (P<0.05) differences in pH and fermentation products.