Affect of Water Table Management on Water Quality
This section will discuss how water table management can affect water quality, particularly nitrate and phosphorus loading.
Nitrate reductions from drainage management systems result from three factors:
- reduced volume of drainage water exported from the system,
- denitrification within the soil profile, and
- deep seepage.
From Questions and Answers About Drainage Water Management for the Midwest (Purdue Extension).
Experiments in Illinois
In experiments in Illinois, reductions of up to 45% in Nitrate and 80% in Phosphate were measured in tile outflow, using controlled drainage. Source: Illinois Agronomy Handbook.
The following table shows the amount of annual flow in inches, along with the amount of nitrate reduction from controlled (managed) drainage in the Illinois study.
|Annual Flow (in)||Annual Nitrate Loss (lbs/acre)|
|Year||Managed||Free||% Difference||Managed||Free||% Difference|
This next graph shows the differences in yield in a managed drainage (MD) setting compared to free drainage (FD)conditions.
It can be seen that at most elevations, controlled drainage yielded slightly higher than conventional (free) drainage in 2009.
In a multi-year Ohio study, controlled drainage systems reduced nitrate loadings by 45% compared to conventional drainage systems. Fouss, J. Drainage Water Management as a BMP to Reduce Nitrate Loss from Cropland to Surface Waters in the Mississippi River Basin and the Hypoxic Zone in the Gulf. Poster, SWCS workshop, 2006.
A standard tile drainage (DR) system was compared over 8 years (1991 to 1999) to a controlled tile drainage/subirrigation (CDS) system on a lowslope (0.05 to 0.1%) Brookston clay loam soil in southwestern Ontario, Canada. Drury, et. al. Water table management reduces tile nitrate loss in continuous corn and in a soybean-corn rotation ScientificWorldJournal. 2001 Oct 25;1 Suppl 2:163-9.
In Phase 1 when continuous corn was grown, Controlled Drainage reduced total tile discharge by 26% and total nitrate loss in tile discharge by 55%, compared to conventional drainage. Drury, et. al. Water table management reduces tile nitrate loss in continuous corn and in a soybean-corn rotation ScientificWorldJournal. 2001 Oct 25;1 Suppl 2:163-9.