The use of mixtures of ammonium salts with lime for upgrading cereal straws

Abstract

The objective of this investigation was to define the optimum conditions for upgrading cereal straws using ammonium salts at ambient temperatures. Storage of barley straw at 20°C for 35 days in the presence of dry or wet ammonium sulphate, ammonium “carbonate” (i.e. carbamate plus bicarbonate) or ammonium bicarbonate gave poor improvements in organic matter digestibility (in vitro) (OMD (vt)), and only the ‘carbonate’ and bicarbonate gave satisfactory upgrading at 90°C for 15 h. However, mixtures of each ammonium salt with calcium oxide (quicklime) or calcium hydroxide (slaked lime) gave good responses under both conditions of storage provided that water was added. Packages of dry mixtures of ammonium sulphate and quicklime (to give 15–39 g ammonia kg −1 straw dry matter (DM)) were attached under the flat surface of round bales of wheat straw and the whole sealed with Silawrap film. Water was introduced and the bales immediately re-sealed. After 7 weeks storage at ambient temperatures, maximum predicted improvements in OMD (vt) (164–168 g kg −1) were achieved with the 30–35 g kg −1 DM treatments, the response to 25 g ammonia kg −1 DM (154 g kg −1) being marginally poorer. Several advantages of this procedure over conventional processes are discussed.