Chemical characterisation of vegetable and arable crop residue materials: a comparison of methods

Although it is widely recognised that chemical composition controls the patterns of decomposition and N mineralisation of crop residue materials, there has been little agreement as to the nature of the most important chemical fractions. We investigated whether this could be attributed to differences in methodologies employed for chemical characterisation of the lignin and cellulose fractions of plant materials. The cellulose and lignin contents of cauliflower, potato, red beet, Brussels sprouts and wheat crop residues were analysed by a number of contrasting methods. These were forage fibre and forest products analyses, which utilise KMnO 4 and H 2 SO 4 respectively to separate the two fractions, and a third method, which employs NaClO 2 . For all the materials, the forage fibre method gave substantially lower amounts of both lignin and cellulose than the other methods. There was correlation between lignin determined by the different methods. Low recovery of lignin by the forage fibre method was found to arise partly from incomplete delignification by KMnO 4 . The cellulose contents given by the different methods were highly correlated. However, it was apparent that the forage fibre method underestimated cellulose, since only alpha‐cellulose was measured. The characteristics of crop residues grown on two sites with different N fertiliser treatments were determined by forest products analysis. The materials were shown to span a range with respect to both lignin (12–26%) and cellulose (17–71%) contents. The chemical characteristics of the materials were not significantly affected by the amount of nitrogen used to produce the crop. © 1999 Society of Chemical Industry