Movement of water and nitrate in the unsaturated zone of Upper Chalk near Winchester, Hants., England

Abstract The increased quantity of nitrate reaching the water table of the aquifer has been assumed by many workers in England to be the result of increased use of inorganic nitrogen fertilizers on farmland. The results of a field experiment are described in which water fluxes were measured in the upper 3 m of the unsaturated zone beneath grass experimental plots to which different rates of animal slurry and inorganic fertilizer were applied. The objectives of the experiment were: 1. (1) To measure unsaturated water fluxes in the upper 3 m of the Chalk. 2. (2) To combine these flux data with measurements of nitrate concentration in interstitial water, to determine nitrate flux. 3. (3) To clarify the physical processes controlling the movement of water, and hence solutes, in the unsaturated zone. Water fluxes have been measured using simultaneous water content and potential measurements. Nitrate nitrogen and chloride concentrations in the interstitial water of the Chalk were measured in centrifuge-extracted water from chalk samples obtained by manual coring. Data have been collected since May 1976, and results from then are described.