title: Does plant uptake or low soil mineral-N production limit mineral-N losses to surface waters and groundwater from soils under grass in summer?
abstract: Summer minima and autumn/winter maxima in nitrate concentrations in rivers are reputedly due to high plant uptake of nitrate from soils in summer. A novel alternative hypothesis is tested here for soils under grass. By summer, residual readily mineralizable plant litter from the previous autumn/winter is negligible and fresh litter input low. Consequently little mineral-N is produced in the soil. Water-soluble and KCl-extractable mineral N in fresh soils and soils incubated outdoors for 7 days have been monitored over 12 months for soil transects at two permanent grassland sites near York, UK, using 6 replicates throughout. Vegetation-free soil is shown to produce very limited mineral-N in summer, despite the warm, moist conditions. Litter accumulates in autumn/winter and initially its high C:N ratio favours N accumulation in the soil. It is also shown that mineral-N generated monthly in situ in soil substantially exceeds the monthly mineral-N inputs via wet deposition at the sites.
authors.affiliation: Environment Department, The University of York, Heslington, York YO10 5DD, UK. malcolm.cresser@york.ac.uk
authors.forename: Ambreen
authors.initials: A
authors.lastname: Bhatti
authors.forename: Colin J
authors.initials: CJ
authors.lastname: McClean
authors.forename: Malcolm S
authors.initials: MS
authors.lastname: Cresser
mesh_terms: D004784:Environmental Monitoring; D005618:Fresh Water / Q000737:chemistry*; D055593:Geological Phenomena; D060587:Groundwater / Q000737:chemistry*; D009584:Nitrogen / Q000032:analysis*; D058458:Nitrogen Cycle; D006109:Poaceae / Q000502:physiology*; D012621:Seasons; D012987:Soil / Q000737:chemistry*; D012989:Soil Pollutants / Q000032:analysis*
chemical_list: D012987:Soil; D012989:Soil Pollutants; D009584:Nitrogen