Abstract

Controlled drainage and sub-irrigation (CDS) are a recommended agricultural practice to improve agricultural water quality and crop productivity. An on-farm study was conducted to evaluate the influence of CDS on nitrate leaching and corn (Zea mays L.) yield in a sandy loam soil in Southwestern Ontario, Canada. A farm was divided into two 1.9 ha plots and planted with corn. One of the plots had a free tile drainage (FD) system, and the other plot was installed with a CDS system. Drainage water volumes and water quality were monitored from 1 May 1996 until 31 April 1997. The cumulative drainage water volume from the CDS treatment was 8% greater than the FD treatment over this period. The flow weighted mean nitrate concentration of the drainage water was reduced by 41% from 19.2 mg N l^-1 for FD treatment to 11.3 mg N l^-1 for the CDS treatment. Hence, the net effect of slightly increased drainage volumes and dramatically lower nitrate concentrations with the CDS treatment resulted in a cumulative nitrate loss of 36.8 kg N ha^-1 compared to 57.9 kg N ha^-1 for the FD treatment. The CDS treatment reduced total nitrate loss by 36% compared to the FD treatment. The soil moisture content (top 120 cm) in the CDS treatment was 21% greater than the FD treatment and the FD treatment had a water table depth that was 49 cm deeper (59%) than the CDS treatment. Therefore, it was not surprising that corn from the CDS treatment had 50% greater transpiration rates (47.4 mg m^-2 s^-1) than the FD treatment (31.7 mg m^-2 s^-1). Similarly, the stomatal conductance was 12% greater with the CDS treatment (0.73 cm s^-1) when compared to the FD treatment (0.65 cm s^-1). The average corn yields were 11.0 Mg ha^-1 from the CDS treatment and 6.7 Mg ha^-1 from the FD treatment which was a 64% yield increase. The CDS treatment also had higher (11%) water use efficiency than the FD treatment. Thus, the crops utilized N and water more efficiently in the CDS treatment which resulted in increased productivity and improved water quality.

Author Keywords: Nitrate; Water table; Controlled drainage; Subirrigation; Tile drainage; Water quality; Sandy loam; Ontario