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Project title

Eutrophication from Agriculture Sources (Phosphorus and Nitrogen) - Effects of Agrictural Practices on Nitrate Leaching - Leaching Soil Investigation Work Package

Primary Funding Agency

Environmental Protection Agency

Co-Funding Organisation(s)

n/a

Lead Organisation

Teagasc

Lead Applicant

John Mulqueen

Project Abstract

Much of the intensive dairy farming in Ireland is located on free-draining unsaturatedsoils overlying important aquifers. This study was undertaken to measure theconcentrations of nitrate-nitrogen (NO3-N) in soil pore water following land spreadingof fertiliser nitrogen (N) dirty water and farm slurry to grassland on a free drainingsandy loam overlying a limestone aquifer. Three rates of fertiliser-N dirty water andfarm slurry corresponding to high medium and low were applied. Chemical fertiliser-N dirty water and farm slurry were applied at the same times as those applied on anadjoining intensively managed dairy farm. Ten experimental field plots including onecontrol plot were laid out following a geotechnical survey to establish soil depth andcharacteristics. There was no evidence of cracks fissures or macropores below thetopsoil (0.3 i- 0.4 m thick). The plots were instrumented to 3 m depth with (i) porousceramic suction samplers to sample the soil pore water at various depths; (ii)tensiometers to measure the pressures of the soil pore water and (iii) neutron probeaccess tubes to estimate soil water contents at different depths. Pore water sampleswere taken weekly during the summer and twice weekly during the winter and analysedfor NO3-N; pore water pressures and soil water content were measured at the same timeas the soil pore water samples were withdrawn. Over the two year period ofmeasurement the NO3-N concentrations in the pore water of the control the low Nfertiliser (174 kg /ha.) and medium N fertiliser (286 kg /ha.) were low in general.However there was a tendency for higher NO3-N concentrations in the pore water ofthe medium fertiliser treatment in spring following late September and late January -early February N applications. The high N fertiliser (387 kg /hectare) gave rise to highNO3-N in the soil pore water. The NO3-N concentrations in the soil pore watergenerally showed no response to summer and winter applications of low (10 mm) dairywaste water applications. Similarly medium (25 mm) and high (50 mm) rates of dairywastewater in summer had little effect on NO3-N concentrations in the soil pore water.However applications of medium (25 mm) and high (50 mm) rates in winter increasedthe NO3-N concentrations of the soil pore water to high levels. None of the slurryapplications of low (15 m3/ha) medium (30 m3/ha) and high (45 m3/ha) had asignificant effect on soil pore water NO3-N concentrations. LEACHN modelling gavefair agreement between measured and modelled NO3-N concentrations in the soil porewater following low medium and high dirty water applications. High initial NO3-Nconcentrations in the soil pore water at the start of the study at depths greater than 1.5m declined to low levels over an 18 to 24 month period and are continuing to decline in9 of the 10 study plots. This indicates that high NO3-N concentrations in soil declinequickly under Irish recharge conditions. There was very good agreement between thecalculated depth of travel of NO3-N solutions in the soil assuming piston flow (alsocalled plug) and the measured depth of travel. This agreement was obtained at 10locations for 13 events confirming the absence of by-pass or macropore flow in the soilat the experimental site.

Grant Approved

�237,975.58

Research Hub

Natural Environment

Research Theme

Improve our Knowledge on the State of our Water Resources and Pressures

Start Date

01/11/2000

Initial Projected Completion Date

n/a