Chemical treatment of lignocellulosic residues with urea

Abstract

A series of comparative studies were undertaken to determine the effects of treatment with anhydrous ammonia and urea mode under different conditions on digestibility and/or voluntary intake of barley straw, wheat straw and maize stover. The following experiments were carried out: Experiment 1: methods of ammoniation of barley straw — in which the treatment of barley straw with anhydrous ammonia (3.56% dry matter (DM) basis and 22.4% moisture content), and with urea applied in solution during baling (6.2% DM basis and 30.5% moisture) or in stack (5.5% DM basis and 35.5% moisture) were studied. Experiment 2: urea levels — wheat straw was treated with urea in increasing dosages (3, 4, 5 and 6% DM basis and 30% moisture). Experiments: modifications in form of application — a comparative study was undertaken of treatments of barley straw with urea in solution with and without plastic cover, together with treatment with urea in solid form (4% DM basis and 25% moisture). Experiment 4: voluntary intake by sheep of wheat straw treated with urea — the influence of moisture content (20, 30 and 40%), the form of urea application (solid or solution) and the addition of crude soya bean (3% DM basis), as a source of external ureases, were studied. The treatments were carried out on 300 kg DM stacks of wheat straw; urea was applied at 3% DM basis. Experiment 5: urea treatment of maize stover — maize stover was treated with urea in solution (4% DM basis and 30% moisture), with urea in solid form (4.3% DM basis and 23.3% moisture), and with urea in solid form (4.3% DM basis and 23.3% moisture) and addition of crude soya bean (4.2% DM basis). All the treatments caused an increase in total nitrogen content and a decrease in neutral detergent fibre content as well as a significant effect ( P < 0.01) on the digestibility of the organic matter (DOM) in the straw. In Experiment 1 the digestibility increased 14.8, 12.8 and 11.7 percentual points in treatments with anhydrous ammonia, urea at baling and urea in stack, respectively. In Experiment 2 the four dosages of urea used were effective, and caused increases in DOM of 7.3, 5.3, 7.4 and 9.0 percentual points for dosages of 3%, 4%, 5% and 6%, respectively. Experiment 3 showed that modifications in the technique were possible, but that the highest digestibility was for plastic-covered urea. Experiment 4 showed that the addition of crude soya bean only had an influence when the treatment was applied at a low moisture level (20%) and that the application of urea in solid form gave an intake of DM lower than that observed for urea in solution. Finally, in Experiment 5 the application of crude soya bean on maize stover was particularly effective both on DOM and on voluntary intake.