The Grain Growing Classroom

By Jochum Wiersma. UM Extension Small  Grains Specialist,
Northwest Research and Outreach Center • wiers002@umn.edu

Air seeders, air drills and seed bed utilization
In recent months I’ve had questions about the optimum row spacing for wheat and barley in this region. In each instance, the question had been prompted by the desire or plan to replace an air seeder equipped with sweeps with an air drill equipped with single disk openers. I’ll first attempt to create some clarity by providing you with some definitions:

Air seeder – a planter which uses a medium or heavy duty cultivator, a central pneumatic seed and fertilizer delivery system, and a ground opener for seed and/or fertilizer placement.

Air drill – a planter which uses either a single or double disk opener and a central pneumatic seed and fertilizer delivery system.

Seedbed utilization – the amount or percent of the seedbed that is utilized, calculated as the width of the band in which seed is placed divided by the distance between openers/shanks.

Using these definitions, a conventional double disk drill with 6” row-spacing would have a seedbed utilization of about 17%, if we assume that the seed is placed in about a 1” wide furrow.  Likewise, an air seeder with 10”spacing, placing the seed into a 3” band, has a seed bed utilization of 30%.

The single disk air drills may offer some key advantages over the older style air seeders – improved depth control and seed placement, in addition to being better suited for low disturbance no-till seeding are key arguments being brought forth.

Researchers in Alberta and Saskatchewan have revisited the question about optimum row spacing for wheat and barley, as direct seeding has become more prevalent across the Canadian prairies.

Using a single disk opener, a research group in Alberta concluded that as row spacing increased from 8 to 12”, grain yield decreased.  The group concluded that as seedbed utilization decreased, so did grain yield. However, another group in Saskatchewan found that increase in row spacing from 4 to 12” did not affect grain yield. 

These seemingly contradicting findings might be explained by the differences in seedbed utilization.  When using narrow openers like the single disk opener, as was the case in the first study, seedbed utilization dwindled from approximately 13% to just over 8% (assuming a 1” furrow).  In the second study hoe openers were used and seedbed utilization in the second study was at least 12%. 

Both studies were in agreement on how the stands responded to the increase in row spacing – initial emergence tended to decrease as row spacing increased, the number of kernels per head increased, while kernel weight tended not to respond.  This underscores that the yield components will (at least partially) compensate for the increase in row spacing.

Widening the row spacings has the obvious advantage of lower capital costs. Likewise, wider row spacing can result in fuel savings, as less horsepower is needed to pull the same width implement.

Can we extrapolate from the research in Alberta and Saskatchewan and reach some conclusions for this region?  It is fair to say that the optimum row spacing for wheat and barley will depend on the type of opener that will be used. Narrower openers like the single disk opener require narrower row spacing, compared to the air seeders equipped with sweeps that place seed into a wider band. 

Based on the current row spacing recommendation for Minnesota and eastern North Dakota, the critical value for seedbed utilization appears to be at a minimum 15%.  When considering the newer style single disk opener air drills, I have suggested not pushing the limit on row spacing too far, and remain close to the standard 6” to 7.5” row spacing of a double-disk press drill.

There are several other dimensions to this subject; like fertilizer placement, competition with weeds, incidence/severity of diseases, and proneness to lodging. We may have to revisit this same topic as newer style openers become more commonplace.