6 Immobilization transforms mineral nitrogen into soil organic matter. Activity of soil microbes is mainly stimulated by ammonium. Immobilized nitrogen is not immediately available for plant uptake, but needs to be mineralized first. Mineralization of soil organic matter (and manure) releases ammonium into the soil. 7 Ammonia volatilization occurs when ammonium is converted to ammonia and lost to the atmosphere. A high soil pH level favours and temperature favour conversion of ammonium to ammonia. If conversion takes place at the soil surface, losses are highest8 Leaching of nitrate occurs mainly during winter and fallow periods when rainfall washes residual and mineralized nitrates below the root zone. Accurate fertilization increases N use rfficiency and reduces the risk of leaching during the growth period and afterwards
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