Influence of growth stage at harvest on fermentative characteristics of Panicum maximum silage

Abstract

An experiment was conducted to investigate the influence of stage of growth at harvest on fermentative characteristics of Panicum maximum silage. The treatments were three different growth stages (early vegetative, boot and full bloom stage) that were ensiled directly or wilted prior to ensiling. Directly ensiled and wilted forage material were mixed prior to ensiling with molasses at 12 and 8 kg/ton dry matter, respectively. Thereafter, each treatment was ensiled in 12 one litre glass jars (bottles). From each treatment, samples of the silage were taken from three bottles at 0, 7, 21 and 120 d post-ensiling for analysis of fermentative characteristics. Growth stage in directly cut silage had no effect on silage pH between days 0 and 21. In contrast, within the wilted groups, a lower pH was observed at day 7 when the plants were harvested at the boot stage than at an early vegetative or full bloom stage. In both directly cut as well as prior wilted silage, a higher lactic acid concentration was recorded on day 7 in the boot stage silage compared to the full bloom stage silage, but on day 21 the boot stage had a lower lactic acid concentration than that of the full bloom stage silage. Growth stage had no effect on the acetic acid concentration on day 7. However, on days 21 and 120 the full bloom stage had a higher acetic acid concentration when the material was directly ensiled. In contrast, in prior wilted silage a higher acetic acid concentration was found in the early vegetative stage silage than in the full bloom stage silage at 120 days post-ensiling. Total nitrogen was lower in the full bloom stage silage than in the early vegetative and boot stage silages. A higher level of ammonia nitrogen was recorded at days 7 and 21 for the early vegetative stage silage as compared to the boot stage silage. A similar trend was revealed in the prior wilted groups between days 0 and 21. Harvesting at the boot growth stage consistently resulted in a good fermentation process with desirable fermentation end products (low pH and higher lactic acid concentration) up to a period of 21 days, but when compared at 120 days post-ensiling the differences between boot and bloom stages were not clearly observed in terms of fermentative attributes, probably due to the confounding effect of undesirable fermentation by entrobacteria or yeast.