Food security

Why do some farm fields look messy after harvest?

That’s the stubble – basically scalped stalks – and other scraps left in the field. The farmer has left this stubble on the field intentionally…but it’s not always possible to do. Let’s look further.

field covered with snow and corn stubble

Corn stubble left up over the winter can provide environmental benefits. Credit SV Fisk

During harvest, a combine (all-in-one machine) mechanically stripped the grain (the kernels) and left the stover – what’s left over after the kernels have been plucked from the ear. This includes the stalk, leaves, and cob. The stover has potential value as a fertilizer if left to decompose. Nutrients are locked in that plant matter. The kernels, of course, are stored in a silo or shipped for sale.*

Some farmers will leave the field as-is over the winter and plant right over it in the spring. In their view, the residue is beneficial. Others will remove and repurpose as much of the organic “litter” as possible – it’s seen as an obstacle in the field.

So which is the best practice? Hoard that litter or keep it clean? It’s not about being a slob or neat freak, it’s a careful cost/benefit analysis.

Farmers can get extra mileage by collecting the otherwise “useless” leftovers and by converting them into biofuels like ethanol. Or, they can graze animals on the fields as a disposal service. All the fiber that humans can’t digest (it’d make you way too regular), animals can eat and convert to usable protein – milk or meat.

A farmer can also decide to plow and bury the residues. Out of sight, out of mind. These tillage systems ensure the residues will slowly decompose and release nutrients. It also keeps the field clean for planting next season. No need to worry about residues gumming up the planter. And overwintering habitat for harmful insects? Denied! Corn Borer caterpillars love to linger in stalks. Plow down the stalks, and the squatters have nowhere to turn. Of course, they can always recolonize from the outside when things warm up next year. There goes the neighborhood.

The problem is that some of these strategies too easily dismiss the contribution of residues as a homegrown fertilizer. In turn, long-term productivity takes a hit. And supplemental fertilizer has to be purchased and applied.

Most importantly, these strategies also rob the soil of carbon. Plant residues are mostly carbon. Soil carbon isn’t really a nutrient – plants get their needs through inorganic carbon dioxide gas from the atmosphere (through photosynthesis)  – but it does have a valuable role.

Organic carbon is locked up in carbon-based life forms like plants and animals (or at least things that were, like fossil fuels). The soil is a major carbon storehouse. This provides a number of benefits like better nutrient/water retention and soil structure. Carbon glues soil particles together – think about cooking without a binding agent like eggs. It also supports a diverse ecosystem of underground critters, many of which recycle nutrients and troll disease-causing organisms. But instead of stockpiling organic carbon as a best practice – our historical approach is to use practices that release it back into the air (as carbon dioxide)! Ideally, we want it to stay locked up in organic soil-bound form.

With that said, farmers are increasingly adopting no-till systems. This means that they minimize any activities like disking or plowing that disturb the soil. This can largely prevent erosion – avoiding the Dust Bowl scenario of the 1930’s. “Keep it [the soil surface] covered” is the motto! It also conserves soil carbon.

Corn stove example

Corn has been replanted in a field covered with corn residues – this type of practice can be good for the environment, depending on the type of soil on the farm. Credit Dave Franzen NDSU

Crops are planted directly into the stubble from the previous year using a no-till drill, a specialized planter. But that mat of organic litter can pose a problem. It can interfere with seedling germination and establishment. Some minor pre-plant decluttering is in order. No-till equipment has “leading coulters” (a vertical cutting blade) that slice into the residue and clear a path to cleanly deposit the seed.

So, to stubble or not to stubble? That is the question. Do we want to squeeze out extra value (like ethanol); tap the nutritional benefits (like a fertilizer); or use as an amendment (something that improves the physical and chemical properties of the soil, where nutritional contributions are more an afterthought – like carbon)? How can the farmer put a dollar figure on these practices – short term gains, long term pains? Vice versa? Only the farmer can answer this question based on their individual circumstances. Every landscape, soil, and crop combination is different. There’s rarely a one-size-fits-all approach. Tailored management is key. With that said, the stover is free recycled fertilizer and carbon. And from a budgeting perspective, it makes sense to at least replace the nutrients that have been removed by the kernels at harvest. A few calculations are in order!

Answered by Timothy Durham, Ferrum College

[*Note that we’re talking about field corn, the starchy type for animal feed and processed foods – not fresh market sweet corn that’s harvested by the ear, kernels still attached to the cob, that must be shucked by some poor soul, like you.]

About us: This blog is sponsored and written by members of the American Society of Agronomy and Crop Science Society of America. Our members are researchers and trained, certified, professionals in the areas of growing our world’s food supply while protecting our environment. We work at universities, government research facilities, and private businesses across the United States and the world.

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