The effect of calcium hydroxide and urea treatment of barley straw on chemical composition and digestibility in vitro

An experiment was conducted to investigate the effectiveness of calcium hydroxide (Ca(OH)2) and urea treatment of straw. Chopped barley straw was treated with mixtures of Ca(OH)2 (0, 30 and 60 g kg−1 straw dry matter, DM) and urea (0, 30 and 60 g kg−1 straw DM) dissolved in 0.81 water kg−1 straw DM and ‘ensiled’ in a polythene bag (1.0 kg per bag) at 15°C or 25°C for 60 days. Control treatment at each temperature involved untreated straw and treatment with 30 or 60 g NaOH kg−1 straw DM dissolved in 0.81 water kg−1 straw DM. Ensiled straws were examined for mould, chemically analysed and assessed for organic matter digestibility (OMD) in vitro. occurred in Ca(OH)2-alone and water-alone ensiled straw, but other ensiled straws were apparently mould free. In the presence of Ca(OH)2 with urea treatment, the nitrogen content of ensiled straw increased more than urea-alone treatment. Analysis of variance of OMD in vitro results showed that Ca(OH)2, urea and temperature interact significantly (P < 0.01). Interactions were found to be non-significant for other parameters (nitrogen, acid detergent fibre and hemicellulose). However, straw ensiled at 15°C with 30 g urea +60 g Ca(OH)2 kg−1 straw DM, 60 g urea +60 g Ca(OH)2 kg−1 straw DM or 30 g NaOH kg−1 straw DM had similar OMD in vitro (67%). Untreated straw OMD was 48.5%. It can be concluded that mixtures of Ca(OH)2 and urea would be the alternative chemicals to NaOH or ammonia for improvement of the nutritive value of straw.