Estimates of annual leaching losses of dissolved organic carbon from pastures on Allophanic Soils grazed by dairy cattle, Waikato, New Zealand

Dissolved organic carbon (DOC) flux on a conventional New Zealand dairy farm was measured for 1 year to assess the contribution from DOC to the total farm C budget. Soil solution was collected using ceramic cups at 60 cm depth. Soil drainage was calculated from a water balance model using rainfall, evaporation and soil water storage data from two eddy covariance systems. Solution was collected approximately every 14 days. The DOC concentration was 5.7 +/- 15.6 mu g C ml(-1) (mean and standard deviation). No significant differences (P<0.05) in DOC concentrations were detected between the four soil types, the two sampling areas, nor date of sampling. The accumulative amount of DOC leached was obtained by combining the soil solution concentrations with the daily estimates of drainage. The mean annual amount of DOC leached was 13-29 kg C ha(-1) y-1and the contributed 2-5% to the net farm annual carbon balance.