Some chemical and physical factors affecting the rate and dunamics of nitrification in urine-affected soil |
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Authors: | R M Monaghan D Barraclough |
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Institution: | (1) Department of Soil Science, University of Reading, London Road, RG1 5AQ Reading, Berks, UK |
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Abstract: | The effects of urinary chloride and nitrogen concentration and osmotic pressure on the nitrification of ammonium in a calcareous soil treated with cow urine were examined. Urinary chloride concentrations of up to 7.4 g L–1 had no effect on the rate of nitrification, as determined by the accumulation of soil nitrate. Osmotic stress, generated using a mixed salt solution, had an inhibitory effect on nitrification at soil osmotic pressures lower than or equal to –1.0 PMa. Nitrification was completely inhibited at a soil osmotic pressure of –2.6 MPa. Accumulation of nitrate after a lag phase of 18 days was noted in the –2.0 MPa soil osmotic pressure treatment, indicating some degree of adaptation or osmo-regulation within the nitrifying population at this stress level. High urine-N concentrations resulted in considerable nitrite accumulations and reduced nitrification activity through the effect of free ammonia. It is concluded that in most temperate grassland soils at near-neutral pH, urinary chloride and nitrogen are unlikely to reduce nitrification rates, except where urine-N concentrations exceed 16 g N L–1. Inhibition due to osmotic stress will be directly related to soil moisture status and may be particularly severe in dry, light-textured soils. |
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Keywords: | ammonia toxicity chloride inhibition nitrate nitrification salt stress urine |
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