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College of Food, Agricultural, and Environmental Sciences


Know Soil Nutrient Needs for Best Continuous Corn Management

February 26, 2007

WOOSTER, Ohio – Knowing a soil's nutrient levels increases options for fertility management and can help maintain productivity in a continuous corn operation.

Robert Mullen, an Ohio State University Extension soil fertility specialist with the Ohio Agricultural Research and Development Center, said that a simple soil test can reveal all that a grower needs to know about a field's condition, which can lead to smarter fertility management and potential alternative options.

"One of the biggest issues facing growers under continuous corn production is the increased amount of nitrogen use – generally 40 pounds more than in a corn/soybean rotation – and the higher costs that come with using commercial fertilizer," said Mullen. "Growers are looking for ways to not invest in as much nitrogen or to cut corners with other crop nutrient requirements. Pay attention to soil tests. The quality of the crop is a function of the operation of the soil."

Soil tests measure the level of nutrients, such as phosphorus and potassium, as well as the soil pH. Though nitrogen is an expenditure that must be made every year on a corn crop, growers have the ability to adjust their phosphorus and potassium levels. By knowing those levels through soil testing, growers under continuous corn production can effectively budget fertility rates, said Mullen.

"Phosphorus and potassium are nutrients that don't deplete every year, like nitrogen. If the soil has an adequate level of phosphorus and potassium, you don't need to add more. Then that money can be used toward the investment of more nitrogen," said Mullen. "Additionally, growers must keep in mind that excess phosphorus can be an environmental hazard in the form of run-off. So maintaining proper levels of phosphorus in the soil is important."

Soil tests can also come in handy to identify the pH of the soil.

"Nitrogen fertilizer is a soil-acidifying reaction, so growers might think about liming more frequently to maintain the pH at around 6," said Mullen. "A soil test will tell a grower the soil pH and whether he needs to lime. If the pH is fine, then you don't have to lime."

If budgeting for additional commercial fertilizer is not an option, Mullen said other alternatives might exist with regard to fertility management.

One option is manure application.

"If you have access to it, manure is a really nice resource of nitrogen, potassium and phosphorus," said Mullen. "Manure can be used to offset some of the commercial nitrogen fertilizer costs. It's just a function of knowing how much to add to the soil."

Mullen said that even with manure application, soil tests are important.

"You can oversupply a field with nutrients that it doesn't need or can pose environmental problems," said Mullen. "Knowing what fields need the manure – not just spreading the manure on the fields closest to the barn – is an important aspect of fertility management."

Additional OARDC research on fertility management includes: comparing phosphorus and potassium fertilization between a corn after corn rotation and a corn/soybean rotation; analyzing nitrogen rates among different corn hybrids; the use of cover crops in crop rotation; and improving manure management.

Mullen recommends that growers conduct soil tests either in the fall or spring after corn or soybeans, or in the summer after wheat harvest. The key is to be consistent about the time of sampling when soil samples are collected. For example, if a grower has historically sampled in the spring, then continue to follow that routine.

For more information on managing a continuous corn rotation, log on to OSU Extension Agronomic Crops Team Web site at

Candace Pollock
Robert Mullen