BELLEVILLE, Ill. — A Southern Illinois University study shows that tillage methods may not affect corn and soybean yields in fields treated with a full fertility regimen.

A long-term fertility plot at the university’s Belleville Research Center compared corn and soybean yields using different tillage methods and fertilizer mixes. The preliminary result is that there is no yield difference among tillage methods.

The study spans 40 years with continuous corn, including 20 years of a corn-soybean rotation. Begun at the College of Agriculture Science’s Belleville Research Center by the late no-till pioneer George Kapusta, it now is tended by Rachel Cook, who teaches soil fertility at the college.

The study encompasses four tillage practices: conventional till, chisel plow, no-till and alternate — two years no-till, one year conventional. Plots were divided into three fertilization applications: nitrogen only; nitrogen, phosphorus and potassium; and a check, with no fertilizer added.

“If you’re putting on your full fertility management, tillage really doesn’t change that much,” Cook said.

That’s good news to farmers who are concerned they may be losing yield with no-till. While yields with every tillage scheme were nearly identical, the bottom line could dictate the tillage method.

“So if not a difference in yield, what else?” Cook said. “Fuel costs. No-till is better on fuel costs. Yield isn’t the final story. The final story is how much money you’re making at the end of the day per acre. There are different costs for different management systems.”

There was no advantage to applying starter fertilizer. But that may be because of the rates put on the plots in the study.

“There are a lot of questions in terms of how effective is starter fertilizer. Out here they found that starter fertilizer really didn’t do much,” Cook said. “If you look at the rates we’re putting on here, it was pretty high rates. We probably weren’t getting much response from starter fertilizer because we were putting on so much anyway.”

While tillage methods didn’t affect yields, rotation made a big difference. In the 20-year corn-soybean rotation trial with full fertility – 1992 to 2012 — corn yielded an average of nearly 190 bushels per acre, while continuous corn yielded an average of only about 135 bushels per acre.

“There was a big yield increase when they switched from continuous corn to a corn-soybean rotation,” Cook said. “Hybrids are changing every year, so take that into account. But we did have more corn yield when we switched to the corn-soybean rotation.”

The NPK treatment yielded much better than the plots with nitrogen only, and, not surprisingly, much more than the check plots, which brought in only about an 85-bushel rate. No-till corn fared worse in the check plots, on which fertilizer had not been applied.

While the long-term study has provided some answers, there still are a number of concerns that are yet to be addressed.

“If you have a bad year, does no-till have more organic matter, so it holds more water – therefore, might do better in a dry year? Those are some of the questions people are interesting in answering,” Cook said. “We’ll continue to look at that. There are so many things we can look at with this experiment.”