Clay-fixed ammonium levels in four Manawatu pasture soils

摘要

Clay-fixed ammonium (NH4+) levels were measured in four pasture soils of the Manawatu region. Fixed NH4+concentrations in dry soil ranged from 170 to 250 mg/kg i.e., 6#x2013;12 of topsoil total nitrogen (N). There were only small seasonal changes in fixed NH4+levels and incubating soil with NH4Cl showed that these soils are close to equilibrium fixed NH4+levels. Fixed NH4+levels rose sharply and declined more slowly in plots treated with urine. Between 5 and 8 of urinary N was temporarily immobiJised. A grazing trial in which dung and urine were withheld from the soil showed losses of fixed NH4+of 20 #x2013; 45 kg N/ha over 3 years. Some fixed NH4+ions were therefore mobilised in this N-depleting system.