Water Quality Research Journal of Canada Vol 47 No 1 pp 30–41 © IWA Publishing 2012 doi:10.2166/wqrjc.2012.007

Economic benefits of controlled tile drainage: Watershed Evaluation of Beneficial Management Practices, South Nation River basin, Ontario

Philippe Crabbé, David R. Lapen, Harvey Clark, Mark Sunohara and Yuan Liu

Controlled tile drainage (CTD) is an agricultural beneficial management practice that can boost crop yields and reduce water and nutrient export from fields to surface water systems. This study examined on-farm incremental net benefits resulting from retrofitting existing tile drainage systems with inline water level control structures that control tile drainage. Corn and soybean yields (2005–2009) were respectively about 3 and 4% higher from CTD fields relative to conventionally drained fields at an experimental watershed associated with the Watershed Evaluation of Beneficial Management Practices (WEBs) program located in the South Nation river basin in eastern Ontario. The marginal cost of CTD employed in this experimental watershed was ∼Can (2006) $30 ha⁻¹. The benefit–cost ratio was 2.6 for corn and 1.6 for soybean. A crude estimate of a payback period (without cost share) was from 3 to 4 years. Assuming all cropland in the entire South Nation river watershed where CTD is suitable, will be under CTD, the net present value of this practice is estimated to yield on farm annually about $(2006) 4 million for both crops. A crude estimate of non-user off-farm benefits of implementing CTD in this manner was ∼$0.4 million per year.

Keywords: controlled tile drainage; JEL Q15; long-run on-farm marginal benefit; off-farm valuation; South Nation River basin; watershed evaluation of beneficial management practices

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