Experimental Archaeology, Horticulture Edition: 2019

March, 2020 – Wendy Munson-Scullin

Several years ago I learned of rows of shallow, pit-like features from the Terminal Late Woodland at East St Louis for which the question was – are these features gardens? This was exciting because the location was a heavy clay soil, which is anything but ideal for growing corn. Clay soil is unyielding of water in dry (or dry-ish) conditions. Clay soils tend to bind nutrients strongly, making them less-available to plants. Clay soil makes corn sad! For real – it curls up, dries out, doesn’t grow well.

I found maize leaf phytoliths in the soil samples sent to me for analysis. I spent a great deal of time scrutinizing those identification – because some common grasses native to North America produce an occasional phytolith form which overlaps with my admittedly restrictive allowance for maize-leaf phytolith morphology. In the soil, you rarely find those forms under native prairie, but careful is the way to go.

I always meant to try planting some corn/maize that way, but I hadn’t committed to it. When this publication came out in 2019, I was studying humic acids in soils – with an eye for improving accuracy of phytolith analysis. Fresh in mind were issues about soil carbon and its complexity. Add to that, in 18 years of working with maize landraces with Michael Scullin, we had some questions about changes in our plants’ growth and yield that pointed to soil management. Because we have been studying ridged field agriculture in Wisconsin and Michigan and learning some of the intricacies of how people maintained the complex and interconnected functions of a natural system, the time was absolutely right for trying out “maize in a hole” planting. This is in miniature (just 1 set of treatments) because space is limited, and it was a test run.

So using the dimensions from the site report linked above, I dug a (roughly) 34 cm wide by 25 cm deep (14 inch x 10 inch) hole in dense, shrinking-swelling Silty Clay Loam and filled it with some carbon-rich topsoil.  Then, four Great Plains Flour Corn seeds were planted in each seed bed.

The hole (left) and the loosened soil that was already there. See the cracks? This soils is a challenge!

Both sets of seeds germinated around the same time. From then on – the plants had surprise after surprise for us.

The hole, now filled with something very different. Purchased at the local garden store for expediency.

The plants in the “hole with good soil added” (HwGS – who doesn’t hate acronyms, right?) were shorter and more slender. They were deeper green and sturdy. The plants in the original soil were taller and paler green. Generally, darker green is a good thing – that indicates adequate nitrogen, among other things. The next difference that appeared was in tillering – those side-stalks or “suckers” that this landrace produces, which can bear flowers and a whole or partial ear of maize – a habit which has been bred out of modern field corn. 

The plants in the HwGS had more tillers. The “original soil” plants had almost no tillers – it was growing up, not out. It should be noted that Great Plains Flour is a landrace (landrace = well-defined, open pollinated variety, not a hybrid) that is supposed to produce tillers and have a bushy growth habit. This is the ideal phenotype for this plant in good soil and in good weather conditions. Not all old maize landraces have that growth habit – some are single-stalked. 

Plants with “good soil” added at left.
Plants with “good soil” added at left.

As soon as it became apparent that this was going to be more than just a fun thing to try, and that nutrients in the added-topsoil may be influencing the outcome – I added some liquid fertilizer to both sets of plants. Reason: This soil tends to be low in phosphorus, a serious limiting factor to plant growth. I didn’t want nutrient deficiency in one set of plants to bias the result. It was clear the plants had something important to teach us.

As the plants in both treatments grew – we saw the proper phenotype for this landrace appear in the HwGS plants – bushy, with leaves close to the ground. Dark green (and some purple) leaves and stalks with stiff-but-flexible leaves. Compact tassles. The other plants grew tall and with fewer stems. 

Plants with “good soil” added at left. This landrace of maize is supposed to look like the one at left.

The final yield difference was a bit frustrating – there was “popped kernel” damage in the largest ear of the HwGS plants, which makes the ear lighter in weight and is caused by irregular rainfall or periods of drying out (we had both). So the yield difference between sets of plants by weight was only about 6.85% greater in the HwGS plants. As can be seen in the photos below – the yield in number of ears was noticeably greater for the HwGS plants.

NOTE: The yield shown in photos below is from the same number of plants in each treatment.

HwGS plants: 83.625 g per plant (below).

Plants in original soil: 77.9 g per plant (below).

For the HwGS plants at this density (which is not as dense as modern field corn is planted), the yield would be 28 bushels per acre, once shelled. In the original soil, 26 bushels per acre, once shelled. Had there been no kernel damage, the HwGS kernel weight would have been higher and the projected yield greater.

This doesn’t sound like a lot in 2019/2020 when yields of 180 bushels per acre or more are the norm in Iowa. But in this clayey soil, despite watering and a light mulch, leaves would fold from heat/water stress on hot, dry afternoons, there was a cool start and more shady days than ideal. Before modern hybrid corn and fertilizers (ca 1940s), corn yields of 30 bushels per acre were average yields.

Good soil management changes plant morphology – you don’t even have to wait until the end of the season – you get feedback in the first few weeks that the plants are loving this. That partly answered a question for me – how did people know their efforts at soil management were working? Did they have to wait until they picked the crop? Nope, you get feedback much sooner than that.

Pulling off yields like in the HwGS plants in a heavy clay soil is nothing short of an garden-engineering miracle. It’s not my idea, though I was fortunate to work with some soil from the site – I’m just ground-truthing what I first heard at a Midwest Archaeological Conference, which was an astute observation of some interesting features exposed in the process of excavations in preparation for work on road infrastructure in Illinois.

This was the idea of Native American horticulturalists who looked at clayey, low-lying soil and envisioned a way to grow corn where corn won’t grow.