Not all cover crops are equal

They all have similar benefits, but how and when they deliver them varies

Students pull up a round of litter bags and root cores from the cereal 
rye-soybean plot.

What’s the best time to plant a cover crop to capture and supply nutrients for the cash crop you’ll be taking to harvest?

A group of U.S. researchers are trying to answer that question and they’re finding different cover crops provide different things at different times.

“It’s like trying to time a meal to come out of the oven,” says Rachel Cook, currently a researcher at North Carolina State University.

The researchers focused on nitrogen because it “is typically the most limiting nutrient in crop production.” The two cover crops, hairy vetch and cereal rye, are two of the most commonly planted cover crops.

They found that hairy vetch and cereal rye had significantly different nitrogen-release dynamics.

“We now better understand the rate and quantity of nitrogen release from two of the more popular cover crops currently in use,” says Cook. “This information can help farmers estimate how much nitrogen they might expect to get and when it will be available.”

The study showed that hairy vetch released more nitrogen overall compared to cereal rye. Nitrogen release was also quicker from hairy vetch plants whose growth had been halted.

“Hairy vetch releases almost all available nitrogen in the first four weeks after it’s terminated,” says Cook. That’s before the major time of nitrogen uptake by corn, which is around week eight after planting. “So, terminating hairy vetch too early could cause losses of nitrogen before the corn crop can get to it.”

Cereal rye, on the other hand, released nitrogen slowly. “This would be beneficial before a cash crop with low nitrogen needs,” says Cook.

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