Cereal straws form a major part of crop residues and are considered an important feed resource in many developing countries. The nutritional value of straw can be enhanced through ammonia treatment using urea as a source of ammonia. Ammoniation involves wetting of straw up to a moisture content of 40 to 50 through application of urea solution. The process of wetting a column of straw where water was applied at the top by dripping through emitters was studied. The relationships between liquid inflow rate, straw bulk density and wetting time, and the moisture retention pattern of straw were established. The exponential growth model was found to be the most appropriate for predicting the wetting process of straw. A mathematical model was developed to simulate the process of wetting of stacked baled straw with urea solution using the dripping method and was validated. The stack height (up to 5 layers of small rectangular wheat straw bales) had no significant effect on moisture contents of straw bales stacked in different layers. The time required for completion of wetting (up to 45 moisture content) with urea solution applied at an inflow rate of 35 g/min per emitter in a 5-layer stack was found to be approximately 50 min. Simulation of the wetting process of a 6-layer stack showed that the time required for completion of the wetting decreased from 57 min to 45 min when the inflow rate increased from 30 to 60 g/min, but the liquid retention efficiency of the stack decreased from about 80 to 49.
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