The effect of water table management on water quality under sandy loam and clay loam soils at the farm scale

Abstract

The water table management systems on agricultural primary nutrients of NO3 -N, TP and K were investigated on three large field sites (a sandy loam site and two clay loam sites, one with no tillage and the other with conventional tillage) located in Southwestern Ontario. The investigation was conducted over a period from May 8, 1995 to July 14, 1998. The purpose of this investigation was to compare tile drainage volume, nutrient mean concentration and nutrient loss between water table control treatments (i.e. controlled drainage with subirrigation-CDS or controlled drainage only-CD) and the free drainage treatment (FD). The results of this study showed that both CDS and CD treatments produced less tile drainage volume compared with FD treatment. At the sandy loam site, the CDS treatment produced less tile drainage volume by 5.3% compared with FD treatment. At the clay loam sites of conventional tillage and no tillage respectively, the CD treatment produced less tile drainage volume by 12.2% and 2.9% compared with FD treatment. Both CDS and CD treatments promoted reduction of NO3 -N mean concentration, respectively by 38.6%, 13.1% and 12.8% at the sandy loam site and at the clay loam sites of conventional tillage and no tillage compared with FD treatment over the study period. Contrary, both CDS and CD treatments promoted increase in K mean concentration by 40.6%, 19.2% and 11.6 % respectively, at the sandy loam site and clay loam sites of conventional tillage and no tillage compared with FD treatment. The CD treatment reduced TP mean concentration marginally at conventional tillage site by 6.9% and at no tillage site by 1.3%, while at the sandy loam site the CDS treatment increased TP mean concentration by 21.9% compared with the FD treatment. Both CDS and CD treatments reduced NO3 -N and TP loss respectively, by 13.4% and 6.7% at the sandy loam site, by 13.2% and 7.1% at conventional tillage site and by 16.3% and 25% at no tillage site compared with FD treatment. In contrast, both CDS and CD treatments increased K loss at the sandy soil site and at the clay loam sites of conventional tillage and no tillage, respectively by 5.2%, 5.5% and 28.1% compared with FD treatment.