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Study: The impact of drainage on crop yield in North Dakota

A new study published on the effects of subsurface drainage on crop yield in North Dakota’s Fargo clay soil has good news and bad news for drainage contractors.

The study, published this month in the Journal of Soil and Water Conservation, investigated the effect of subsurface drainage, crop rotation, and tillage on crop yield in Fargo clay soil. It was conducted by Umesh Acharya, Aaron Lee M. Daign and Amitava Chatterjee, who work in the soil science department at North Dakota State University.

The researchers say the study was motivated by the growing popularity of subsurface drainage for the clay soils of the Northern Great Plains of the United States and the need for “evidence-based recommendations” for these specific soils.

The field trials revealed in some years, the “check” or no drainage field yielded higher than fields that were tiled, and in other years, there was no noticeable difference in yield between drainage treatments.

While yield is not the only important measurement in a field, these lacklustre results on the impact of tile drainage reduce overall confidence in the practice for this particular area.

The study

The four year study was conducted in the Red River Valley of eastern North Dakota from 2014 to 2017. The researchers compared differences in drainage treatments, crop rotation, and tillage.

When it came to subsurface drainage, the researchers compared conventional drainage, controlled drainage and a no drainage check.

When it came to crop rotation, the researchers compared a continuous corn and a corn-soybean rotation.

Finally, for tillage, researchers compared working with a chisel plow, strip tillage and no-till.

The study concluded that these factors, drainage, crop rotation, tillage and their interactions, “significantly affected corn yields.”

No drainage check produces better yields in some years

Corn yield was similar between drainage treatments except during 2014 and 2015 when the no drainage check yielded 22 percent and 8 percent higher, respectively, than drained treatments.

The North Dakota State University researchers also published another study earlier in 2019 that pointed to how drainage design, and particularly spacing and depth, also had an impact on crop yield. In this earlier three-year study, they concluded that “narrow spaced (nine meters, versus 12 or 15 metres) subsurface drains in poorly drained, frigid clay soils may increase corn and soybean yield during wet years.”

Lower yields with continuous corn

When it came to crop rotation, corn in rotation with soybeans produced higher yields than continuous corn in the last three years of the study. The corn-soybean rotation produced 28 percent, 53 percent and eight percent higher yields in 2015, 2016 and 2017 respectively.

No-till might not be the answer

On the frigid clay soils used for the study, the fields that were chisel plowed had higher corn yields than the other tillage treatments. The chisel plow corn yielded 12 percent, nine percent, and eight percent higher than other tillage treatments in 2014, 2016 and 2017.

However, the researchers note that strip tillage yielded five percent higher in 2015 than the no-till treatment.

Given all the other benefits of reduced tillage for soil health and land stewardship, strip tillage is sometimes referred to as the “best of both worlds” when it comes to whether or not to work the ground. Strip tillage is a form of conservation tillage that only disturbs the portion of the soil that will contain the seed row leaving the spaces between the row untouched and covered by crop residue.

Drainage and tillage did not affect soybean yields throughout the study, except during the drought year of 2017. During 2017,  the chisel plowed fields averaged across all drainage treatments but chisel plowed fields in combination with no drainage yielded 18 percent higher than all other treatments.

Final results

When the researchers compiled all the results from the four year study, they found the best mix of factors for higher corn yields.

They concluded that, “Among all drainage, tillage, and crop rotation combinations, the four-year corn yield average was significantly highest for the no drainage, chisel plow, and corn-soybean rotation combination.” With this combination, the average corn yield was 163.42 bushels per acre or 10.98 metric ton per hectare.