Agricultural Drainage

Bulletin 871-98

Michigan

Research and Demonstration

Research and field demonstration projects have been coordinated by Michigan State University at several sites located in the south central area of the lower peninsula of Michigan. A first project was installed in 1984 at the East Lansing Campus site to compare subirrigated yield to overhead irrigated yield. The effect of water table depth on plant physiology and nitrate-N and atrazine transport and distribution was also studied.

Field demonstrations to examine the effects of drain pipe spacing on water table management system performance began in 1985 at Bannister on a poorly drained, fairly heavy clay loam, and in 1986 at St. Johns on a sandier and poorly drained soil series. In 1987, the Bannister site system was modified to allow for study of effects of subirrigation on nutrient and pesticide concentrations and loading in discharge water and the soil profile.

In 1989, a research study was initiated near Unionville to comprehensively compare water table management by subirrigation to both conventional subsurface drainage and to the same soil without subsurface drains.

Water Quality Results

At Bannister:

• For 20 months of monitoring beginning in 1987, the total nitrate-N delivered from the field to the outlet ditch by the subsurface drainage system was reduced 64% by subirrigating (see graph).

• For the same period subirrigation had little effect on the dissolved orthophosphate-phosphorus delivered by the drainage system.

Bannister and Unionville nitrate-N and orthophosphate-phosphorus
loadings (for subsurface drainage flow only at Bannister; subsurface
drainage flow + overland flow at Unionville).

At Unionville:

• For the 1990 and 1991 growing seasons (12 months of monitoring), water table management by subirrigation reduced nitrate-N leaving the field by 58% and dissolved orthophosphate-phosphorus by 16% compared to conventional subsurface drainage (see graph at right).

• For the months of May through October, subirrigation reduced the average drainage flow nitrate-N concentration from 41 mg/L to 12 mg/L in 1990 and 18 mg/L to 10 mg/L in 1991.

• The average orthophosphate-phosphorus concentration in subsurface drainage flow was nearly equal for both growing seasons.

• The total drainage volume, surface and subsurface, was 17% greater for subirrigation than for conventional subsurface drainage. However, subirrigation increased the volume of surface drainage by only 7%.

Side by side comparison of subirrigated to conventional subsurface drained crop yields have been made at all of the above research sites plus other Michigan locations.

• The average of 24 measurements for subirrigated corn was 173 bu/acre. Eight subirrigated soybean yield measurements averaged 53 bu/acre and five subirrigated sugar beet measurements averaged 25 t/acre.

• Comparison yields measured from adjacent subsurface drained fields without subirrigation averaged 138 bu/acre for 16 corn yield measurements, 37 bu/acre for two soybean yield measurements and 22 t/acre for five sugar beet yield measurements.

• The yield results suggest that for field crops, at present market value, subirrigation provides a positive return on investment until the capital cost of subirrigation improvement exceeds about $600/acre more than the cost of a conventional subsurface drainage system.

• The cost of water table management by subirrigation is less than other irrigation methods both in terms of capital cost and operation cost for cropland that requires subsurface drainage.

For a substantial percentage of Michigan cropland, water table management by subirrigation is feasible and often provides both water quality and economic benefit. Fields that are suitable have:

• l poorly drained soils with slopes that are flat or gently sloping;

• l an irrigation water source that will provide, for the entire growing season, good quality water at a rate that will meet the evapotranspiration needs of the crop plus water that may be lost by seepage;

• l an energy source for pumping irrigation water; and

• l a conservation plan that addresses potential conservation problems.

The field studies, coupled with information from farmers with water table management experience, has confirmed that water table management systems must be properly operated to achieve the benefits possible. Water table management systems that are not properly operated result in wasted water, increased discharge of nutrients and pesticides, wasted consumed energy, and reduced yields.

The average yields for plots that are subirrigated (SI) compared to the
average yield of plots that are subsurface drained without subirrigation
(DO).