A COMPARISON OF FARM-SCALE METHODS OF APPLICATION OF SODIUM-HYDROXIDEON THE NUTRITIVE-VALUE OF A WINTER-WHEAT STRAW

An experiment was devised to test five commercially available systems of treating straw with sodium hydroxide (NaOH) for their efficiency an d effect on the chemical composition, digestibility and energy value i n vivo of the resulting straws. Winter wheat straw (cultivar 'Mercia') was baled and treated as follows. Treatment T1, untreated and chopped through a Stropper box; T2, JF 2000 machine; T3, tub grinder (large r ound bales); T4, stropper box (large, high density bales); T5, stroppe r box (large, round bales); T6, forage harvester and mixer wagon. Trea tments T2-T6 all had NaOH applied as a 32% (w/v) solution to give appr oximately 45 kg t-1 of straw dry matter (DM). NaOH treatment, regardle ss of method of application, reduced the hemicellulose content of the DM, and the gross energy content, though the level of change was varia ble between treatment methods. The variability noted for buffer solubl e lignin was strongly correlated with the apparent level of NaOH addit ion calculated from the measured sodium content (r2 = 98.8%). Overall, digestible organic matter in the DM (DOMD) measured in vivo increased significantly (131 g kg-1) in the straw with NaOH treatment. The chan ges in DOMD in vivo as a result of method of application of the NaOH w ere significant only for T4 and T6 (595 and 559 g kg-1, respectively, P<0.05); this difference corresponded to the highest and lowest NaOH a pplication rates, respectively. Metabolizable energy (ME) content also increased significantly as a result of NaOH treatment by 2.42 MJ kg-1 DM (P<0.05), but method of application had no significant effect. Rat e of application of NaOH had an effect on the degree of upgrading and was dependent on the estimation of rate of straw throughput by the ope rator and was not constant. T2 and T6 appeared to be the only equipmen t to give the correct rate of NaOH application.