Corn producers can often increase profit by minimizing or eliminating tillage, but in some situations this can reduce corn yields, say researchers at Kansas State University, the University of Guelph and the International Plant Nutrition Institute.

The yield reduction results largely from cool, moist soil conditions for the seedling, especially on fine-textured or poorly drained soils. Fall strip-tillage — also called zone tillage — is one way of overcoming some of the problems with no-till while retaining many of its benefits.

Strip-till opens up new fertilizer-placement options. During the tillage operation, plant nutrients can be placed several inches deep, directly below the seedbed. This can be an economical and agronomically efficient way of supplying some of the crop’s nutrient requirements, particularly for nutrients with limited mobility like phosphorus and potassium. Furthermore, getting some of the nutrient application job done in the fall helps streamline spring field operations, resulting in a better chance of timely planting.

The concept of tilling narrow strips in the fall is attractive for several reasons:

• It requires one-third to one-half the time and fuel of a fall mold board plow/spring secondary tillage system.
• It provides a zone of bare soil that warms and dries more quickly in the spring.
• It retains residue cover on the untilled land, protecting against wind and water erosion and maintaining infiltration.

One drawback of strip-till is it may disturb the network of mycorrhizae fungi that can help the corn seedling take up nutrients. Pure no-till may take better advantage of these biological partners of the corn plant, but the drawbacks of colder soils and later planting often outweigh the benefits.

A Kansas State University tillage research project was initiated in the fall of 2002 where fall strip-till is being compared to no-till. Timing (spring vs. fall) of nutrient applications within strip-till treatments is being evaluated, as is nitrogen rate (0, 40, 80, and 120 pounds per acre) across all treatments. Phosphorus and sulfur are not variables in the experiment, and are being applied at rates considered adequate.

In the fall-application timing treatment, all fertilizer is placed approximately 5 to 6 inches deep during the strip-till operation. Fertilizer in the spring treatments is placed in a 2-by-2-inch configuration.

Fall strip-till significantly increased corn yields over no-till in 2003. Application of nutrients during the fall strip-till operation resulted in yields similar to the spring applied fertilizer, indicating that fall application of nutrients with strip-till is an effective management practice.

Additionally, early-season soil temperatures were higher in strip-till, thus providing an advantage in emergence, early season growth, and stand uniformity over no-till.

In Ontario, previous research on corn following wheat found that fall strip-till produced yields equal to or slightly better than those with no-till.

However, in the past 2 years, at two sites where corn followed soybeans, strip-till produced yields intermediate between no-till and full tillage with a fall moldboard plow.

Drier Soil With Strip-Till

These yield data do not fully reflect the advantages of strip-till, because all plots were planted the same day. The strip-till plots were often ready for planting a few days earlier than the no-till plots.

Across seven sites in 2002, strip-tilled soils contained 20% moisture in the seed zone to 6 inches deep, compared to 30% in no-tilled soils. The drier soil facilitates earlier planting which potentially can provide an additional yield boost.

In field trials carried out from 2000 to 2002, corn responded to phosphate and potash fertilizers applied in either fall or spring. Fall-applied phosphate and potash boosted yields by an average of 4% (12 site-years). Spring-applied, the same two nutrients boosted yields by 8% (13 site-years).

There appeared to be little interaction. The response to spring application occurred whether fall fertilizer had been applied or not. Responses to fertilizer were similar for each tillage system. Soil test levels ranged from medium to high for both phosphorus and potassium.

In the 2003 growing season, a low-fertility field in Ontario demonstrated how responses to fall and spring fertilizer can depend on tillage. The soil test was medium for phosphorus (16 parts per million [ppm] Olsen) and low-medium for potassium (58 ppm).

Seedlings showed visual symptoms of phosphorus and potassium deficiencies in the check plots. The trial conducted in this field comprised tillage treatments subdivided to receive combinations of fall-and-spring applied phosphate and potash, with a constant level of nitrogen (27 pounds per acre as starter, plus 134 pounds per acre as sidedress).

Responses to either fall or spring-applied phosphate and potash were larger in no-till and fall strip-till than in moldboard-plowed soil. Application in the fall was more effective in strip-till than in no tillage.

However, in general, the spring-applied fertilizers were more effective than those applied in the fall, even though the rate applied in the spring was only half that applied in the fall (125 pounds per acre of each of P 2O5 and K 2O).

Applying both fall and spring fertilizer produced yields that were not significantly higher than spring fertilizer alone. Overall, the results indicate the importance of adequate phosphorus and potassium fertility for successful performance of reduced tillage systems.

Summary

We need to learn more about optimum placement and timing of nutrients in modified tillage systems. The Ontario research indicates that phosphorus and potash produce larger yield responses applied in the spring than in the fall, but also that there appears to be an independent yield boost from fall-applied fertilizer.

On the other hand, in Kansas there was no significant difference between fall and spring application of fertilizer in a strip-till system. We encourage continued on-farm testing of fertilizer placement and timing in combination with conservation tillage.