A cover crop of wheat or rye sown in April moves about 1 inch of water per acre per day through plant transpiration, University of Missouri Extension field specialist Caleb O'Neal told growers reviewing soil health options after harvest. The figure anchors his pitch that producers should run their fields the way they run a chequebook.

"If we want our bank accounts to accumulate wealth, we need to consistently make the sum total of our deposits more than the sum total of our withdrawals," O'Neal said. "If my harvest takes a certain amount of nutrients away, I, at a bare minimum, need to replace what was taken."

What does the banker metaphor change in the field?

The framing forces a whole-farm accounting of two assets: water and carbon. O'Neal treats evaporation as inflation, a loss growers cannot prevent. Transpiration, by contrast, is an investment. Water leaves the field through the plant, then returns value as the crop captures carbon, feeds soil biology and builds structure.

"Water vapor leaving our farm, it's like inflation," O'Neal said. "There's nothing we can do about it, and it makes us really mad when you've got money in the bank, but it's devaluing."

The practical rule: keep the soil covered. Bare ground loses moisture to evaporation. A green crop routes water through transpiration instead.

How much water can a cover crop move?

A wheat or rye cover drilled in April can soak up roughly 1 inch of rain per acre per day through transpiration alone, O'Neal said. Planting beans into crimped rye or another cereal cover holds the same or higher total water use, but the share lost to evaporation drops sharply.

"You're still losing similar or maybe more water through the transpiration needed to grow that cover crop, but your evaporative water loss has been reduced greatly," O'Neal noted. "That's currency management. That's being smart with the resources on your farm."

Where does the carbon go?

Earthworms do most of the heavy lifting. Each worm digs tunnels and leaves carbon-rich deposits that lift porosity and water infiltration. Diversity in the rooting zone keeps the population in place. Worms drag decaying leaves into carbon-deficient layers, banking organic matter where it counts.

"The more plant and root activity, the plant is going to create sugars and send out root exudates, which are sugars," O'Neal said. "But sugar has a lot of carbon in it, and the more of that we can pump into the soil, the more soil we can build."

His one-line verdict: "Productive soils are built, not bought."

Which cover crop fits which problem?

O'Neal matched five common species to specific field goals:

• Cereal rye. Produces 6 to 8 inches of biomass when crimped. Fibrous roots fracture shallow compaction down to 6 inches. High carbon-to-nitrogen ratio and a strong nitrogen scavenger. Terminate while vegetative for a nitrogen release, or let it mature for the opposite effect.
• Wheat. Runs two to three weeks behind rye, giving growers more time to terminate or incorporate green. Lower biomass, so weaker weed suppression.
• Crimson clover. Pairs with cereal grains. Fixes nitrogen and stays upright alongside spring rye to balance the carbon-to-nitrogen ratio.
• Hairy vetch. Low carbon-to-nitrogen ratio and heavy nitrogen fixation. Combines well with crimson clover for the following cash crop.
• Sunflowers. Fits a summer annual mix. Roots scavenge calcium, sulfur and potassium and break compaction. Harvest is tricky because the seed is oily, but the crop is gaining cash value.

"When we select a cover crop species that can really target specific issues we're seeing in our soil, we can actually select cover crops that are uniquely capable of alleviating those deficiencies," O'Neal said.

Termination timing matters as much as species choice. It sets the end goal of the stand.

What should farmers do before winter?

O'Neal's prescription: keep a "coat" of living plants on the field for as many months as possible. Cereal grains such as rye, wheat, triticale and barley hold soil structure through the cold. Austrian winter peas and crimson clover add a nitrogen-fixing legume to the mix.

"If we remember to deposit more than we withdraw and keep something green and actively growing in our soils for as much of the year as possible, we'll be steering our soils in the right direction," O'Neal said.

Growers planning cover crops for the 2026 season should match species to the specific deficiency they want to fix, terminate at the growth stage that delivers the right carbon-to-nitrogen outcome, and weigh drilling dates against April transpiration rates of roughly 1 inch per acre per day.