Kinetics of urea hydrolysis and binding of ammonia to wheat straw during ammoniation by urea.

Chaffed wheat straw treated with urea (5% wt/wt) alone or with rumen liquor, a source of urease (EC 3.5.1.5), was stored in polythene bags at 4, 22, and 37 degrees C up to 60 d. Moisture concentration was adjusted to 40%. Urea remaining in the straw and ammonia concentrations in the bags were measured on 2, 4, 8, 12, 16, 25, 40 and 60 d. Urea hydrolysis increased exponentially with time. Hydrolysis of urea was highest at 22 degrees C followed by 37 and 4 degrees C. Addition of rumen liquor substantially increased rate of urea hydrolysis at all temperatures studied, suggesting that treatment time can be reduced by addition of rumen liquor. Rates of ammonia binding at different temperatures were in the order 22 degrees C greater than 37 degrees C greater than 4 degrees C. No hydrolysis of urea was observed up to 7 d of storage at 22 and 37 degrees C when straw was autoclaved and the treatment was carried out under aseptic conditions.