A comparison of methods for the determination of dry matter concentration in grass silage including an extraction method for water

Further investigation into silage dry matter determination methods has been prompted by the urgent need to replace toluene distillation with determination method(s) which offer less risk to health and safety. The aim of this investigation was to establish the suitability of gas chromatography (GCDM) and Karl Fischer titration (KFDM) as alternative methods for the routine determination of silage dry matter. These methods were compared with the current methodology of dry matter determination by toluene distillation with corrections for alcohols (TDM), oven drying (ODM), and volatile corrected oven dry matter (CODM). An extraction method for water from grass silage was optimized using 71 grass silages produced from predominantly perennial ryegrass swards. These silages, which ranged from 114-471 gkg(-1) oven dry matter were analyzed using six methods including a modification of the standard toluene distillation method where the distillate was analyzed by Karl Fischer titration (KFTDM). Overall there was a 13.4 gkg(-1) DM difference (P < 0.01) between the ODM and TDM determinations. Both the dry matter concentrations determined by gas chromatography (GCDM) and Karl Fischer titration (KFDM) methods gave significantly higher results than TDM except in the highest DM range, but were not significantly different from KFTDM. Overall the results from the six methods could be-grouped into three groups: ODM, TDM, and CODM, KFTDM, GCDM, and KFDM with means of 232.3, 245.7, and 253.6 gkg(-1), respectively. The mean 7.9 gkg(-1) increase in DM of the methods over TDM suggests that some volatile and water-soluble components which commonly occur in silage are not accounted for. The results suggest that estimation of water by either gas chromatography or Karl Fischer titration provides a safe, and an accurate improvement in the methodology of dry matter determination. The gas chromatographic procedure has the advantage of low costs/sample with the possible additional benefits of batch processing and automation. (C) 1997 Elsevier Science B.V.