A soak-and-press method for the alkali treatment of fibrous crop residues. Calcium hydroxide and sodium hydroxide treatments of rice straw

Abstract

Laboratory experiments showed that calcium hydroxide (as a laboratory reagent or as a commercial preparation), or calcium oxide, applied to rice straw by soaking for 24 h was as effective in increasing in vitro organic matter digestibility as sodium hydroxide applied by the spray method. Subsequently, twelve mature sheep, weighing 47–54 kg, were allocated to two groups and fed with diets containing rice straw treated with either the commercial preparation of calcium hydroxide or with sodium hydroxide. To provide equivalent amounts of base, the calcium hydroxide was applied at 9 g per 100 g straw dry matter and sodium hydroxide was applied at 5 g per 100 g straw dry matter. The calcium hydroxide was mixed with 1·2 litres of water per 100 g straw and allowed to react for 24 h, after which the straw was removed, pressed at 1 kg-cm 2 to remove some of the excess water, and then dried. The sodium hydroxide was mixed with 100 ml of water per 100 g straw, sprayed on to the straw in a horizontal mixer and allowed to react for 24 h; the treated straw was then dried. Prior to feeding, each treated straw was supplemented with 2·5% urea, 0·6% potassium sulphate, 3% molasses and 3% minerals. Digestibility and ad libitum intake measurements were made during the last 10 days of a 28- to 33-day experimental period. The diet containing rice straw treated with calcium hydroxide had a similar organic matter digestibility to the diet containing rice straw treated with sodium hydroxide (61 and 63%, respectively), the ad libitum organic matter intakes were similar (66 and 62 g kg W −.75 day −1, respectively), and the calculated intakes of digestible organic matter were similar (40 and 39 g kgW −0·75) day −1, respectively).