A comparison of farm-scale methods of application of sodium hydroxide on the nutritive value of a winter wheat straw

Abstract

An experiment was devised to test five commercially available systems of treating straw with sodium hydroxide (NaOH) for their efficiency and effect on the chemical composition, digestibility and energy value in 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 round bales); T4, stropper box (large, high density bales); T5, stropper box (large, round bales); T6, forage harvester and mixer wagon. Treatments T2–T6 all had NaOH applied as a 32% (w/v) solution to give approximately 45 kg t −1 of straw dry matter (DM). NaOH treatment, regardless of method of application, reduced the hemicellulose content of the DM, and the gross energy content, though the level of change was variable between treatment methods. The variability noted for buffer soluble lignin was strongly correlated with the apparent level of NaOH addition calculated from the measured sodium content ( r 2 = 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 changes in DOMD in vivo as a result of method of application of the NaOH were 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 application 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. Rate 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 operator and was not constant. T2 and T6 appeared to be the only equipment to give the correct rate of NaOH application.