Electrometric titration as a method of predicting the chemical composition and corrected dry matter concentration of silage

Abstract

While near infra-red reflectance spectroscopy (NIRRS) has now been widely accepted as a technique for the routine prediction of some components in grass silages, there is often a need for additional descriptive information on the products of fermentation and nitrogen fractions to give an overall measure of the silage quality. 136 silage samples which had been obtained from farms across Northern Ireland over a 2 year period and which had been selected as representative of a broad spectrum of silage types, were analysed by normal wet chemistry techniques for dry matter, nitrogen components, volatile fatty acids, lactic acid, and residual sugar concentrations. The silages were also assessed by titration of press-juice using an automatic computer controlled titration system. The titres corresponding to fermentation products and nitrogen fractions were extracted from the titration curves about the pK values of the component groups. Linear regression analysis of analytical data against predicted component concentrations for Kjeldahl nitrogen, ammonia nitrogen, total volatile fatty acids and lactic acid gave R 2 of 0.91, 0.86, 0.88, and 0.87, respectively. Prediction of known volatile corrected dry matter (kvcTDM) using volatilities of ammonia, volatile fatty acids and lactic acid during oven drying from previous work gave R 2 = 0.95 and S.E. of prediction of 5.7 g kg −1 fresh silage. The titration technique offers an alternative method for routine silage analysis in advisory work. The method has the benefit of being rapid, inexpensive to operate and it can be easily automated.