Corn producers can often increase profit by minimizing or eliminating tillage.
However, in some situations, this can reduce corn yields, especially with cool, moist soil conditions for the seedling in fine-textured or poorly drained soils.
Strip-till opens up new fertilizer placement options because 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.
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 (Figure 2). 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 (Figure 2). 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.
