There are not many long-term studies in the Dakotas comparing no-till and conventional-till yields. But one has been going on since 1991 at South Dakota State University’s Southeast Research Farm in Beresford, S.D.

Key results from the farm’s 2018 annual report — written by Peter Sexton, SDSU associate professor and Extension sustainable cropping systems specialist — include:

Corn

Two-year rotation. From 1991 through 2018, in the two-year corn-soybean rotation, corn in the tilled plots averaged 6.1 bushels per acre more than corn in the no-till plots.

Diverse rotation. With a more diverse rotation, there was no yield benefit observed with tillage in this trial. In fact, corn in the no-till plots showed a small numeric yield advantage in the longer rotations (1.3 to 1.8 bushels per acre), but it was not statistically significant. Average yield across rotations showed essentially the same yield for the tilled and no-till plots.

2018 tillage. In 2018, plots that received tillage showed 11 bushels per acre more yield on average than plots under no-till management.

2018 seed weight. In 2018, individual seed weight was significantly higher in the tilled than in the no-till plots, which is an indicator that plants in the no-till plots may have experienced some late-season stress. The year 2018 was marked by above-average rainfall and some disease pressure from anthracnose stalk rot, which was expressed later in the year. These circumstances may have favored the tilled plots in the 2018 season. 

2018 cover crop. No significant differences from use of a cover crop were observed for 2018 in this trial. One factor with this is that a large component of the cover crop biomass was volunteer cereals, particularly oats, in this past season. Previous work at the Southeast Farm suggests that cool-season broadleaves, such as radishes and peas, tend to benefit corn yield, while grass-based cover crops tend to have no effect on the yield of the following corn crop.

Soybeans

No-till management. Across rotations, soybeans on average yielded 1.8 bushels per acre more under no-till management than under tillage over the course of the study.

Two-year rotation. In the two-year corn-soybean rotation, soybeans in the no-till plots on average yielded 1.4 bushels per acre more than did soybeans raised with tillage.

Three-year rotation. Soybeans in the three-year rotation of corn-soybean-small grain tended to yield 1.3 bushels per acre more with no-till.

Four-year rotation. In the four-year rotation of corn-soybean-small grain-alfalfa/field pea/soybean, soybeans showed a 2.5 bushels per acre yield advantage with no-till production.

2018 no-till. In 2018, no-till soybeans showed on average 2.8 bushels per acre greater yield than soybeans raised under tillage. This difference was statistically significant.

Winter rye cover crop. There was no consistent yield trend one way or another associated with use of a winter rye cover crop on soybean yield. In the conventional till plots in a two-year rotation, soybeans following a rye cover crop tended to yield less than in those that didn’t follow a rye cover crop, but that effect was not consistent across other treatments nor in other years of this study.

Conclusions

On average, the value of the yield gain in soybeans pretty much balanced out the observed yield loss in corn yield in a two-year rotation. In more diverse three- and four-year rotations, there was no corn yield loss observed in corn under no-till management, but there was still a better yield for no-till soybeans.

This study did not utilize traffic control for the first 20 years that it was run, nor did it utilize banding of N at planting for corn. These are two points where a farmer transitioning to no-till might be able to improve on the results shown here. These two practices were not considered 28 years ago when the trial began.

This study does not yet provide information about soil health.

“Is soil carbon increasing in the no-till/long term rotation plots?” asks Anthony Bly, SDSU Extension soil health specialist. “We are currently looking for greener ethanol and it could be very important to show that we can sequester carbon and grow corn for ethanol. Also, the ownership, extra fuel and time inputs into the conventional tillage needs to be considered.

“All things considered, I think it is worth the switch to no-till. It was indicated that in 2017, yields were excluded because of tile drain installation. I have been a witness to this site since it began.  This site can be very wet.  I think it is a great supportive point that the no-till yields were not substantially less.  This site is a good example that no-till can compete in wet soil.”

Important details

This trial is laid out in a randomized complete block design with four replications. Plot size is 60 by 300 feet. The no-till plots have not been tilled since the trial began in 1991. The tilled plots have been chisel plowed in the fall following corn or small grain harvest and worked in the spring with a field cultivator. Where wet conditions in the fall prevented chisel plowing corn stubble, the tilled plots were disked in the spring and then field cultivated.

The three-year rotation started with corn, soybean, small grain, and then for several years field pea was substituted for small grains. Later, it was switched back to corn-soybean-small grain.

The four-year rotation initially included alfalfa, then after some years was changed to include peas, and later was changed again to include two soybean crops (corn-soybean-winter wheat-soybean).

Since 2013, the rotation has been corn-soybean-oat-winter wheat.

Three seasons were dropped from the data set: in 1993, no crops were planted due to excessive moisture; in 2005, the initial herbicide application for burning down weeds was applied late (well after planting); and in 2017, tile drainage lines were installed along the north and south edge of each plot.

For more information, read the complete report at online, or contact Ruth Steven at the Southeast Research Farm at 605-563-2989 to request a free hard copy of the annual report.