Source: Keith Janssen, Soil Management Agronomist, East Central Experiment Field, Kansas State University

Corn growers who have automatic guidance systems technology (e.g., GPS and autosteer) can plant corn directly on top of previously established strip-tilled fertilized rows, but this might not be the best location for planting.

Depending on how soon the corn is planted after the fertilizer has been applied, and the rate and forms of fertilizers applied, the best location for planting may be some distance away from the strip-tilled fertilized rows. Strip-tilled fertilized rows could have air pockets under the row, might be dry or cloddy, or could have excessive levels of fertilizer salts or free ammonia. On the other hand, planting too far away from the strip-tilled fertilized rows might reduce benefits from residue management including warmer loosened soil and rapid root-to-fertilizer contact.

Procedures
To determine the best location for planting corn relative to strip-tilled fertilized rows on fine-textured soils in eastern Kansas, we conducted tests at two locations over three years in east central Kansas. Treatments included planting corn directly on top of the strip-tilled fertilized rows, and 3.75, 7.5, and 15 in. off the center of the rows.

The strip-till fertilization application was performed 1 day before planting in 2006, two weeks before planting in 2008, and 2.5 months before planting in 2009. Fertilizer was applied at a standard rate (120-30-10 lb/a). The fertilizer source was a mixture of dry urea, diammonium phosphate, and muriate of potash. Depth of the strip-till fertilizer application was 5 to 6 in. below the row.

Results
Plant populations. In 2006 and 2008, plant populations were higher for corn planted 3.75 in. off the center of the strip-tilled fertilized rows than for corn planted directly on top of the rows. This was expected in 2006 because the strip-till fertilization operation was performed only 1 day before planting and the soil was loose and had air pockets under the row. In 2008, when there were 2 weeks between the strip-till operation and planting, plant population was still increased by planting just slightly off the strip-tilled fertilized rows. No differences in plant populations occurred in 2009, when the strip-till operation was performed 2.5 months before planting. 

Early season growth. Early season corn growth at the 2- to 3- and 6- to 7-leaf growth stages tended to be better for corn planted directly on top of the strip-tilled fertilized rows or just slightly off (3.75 in. off) than for corn planted 7.5 and 15 in. off the center of the rows. Planting corn 7.5 in. from the center of the strip-tilled fertilized rows reduced early season corn growth 12 percent on average, and planting 15 in. away reduced early season growth 38 percent.

Yield. In 2006, yield of corn planted directly on top of the strip-tilled fertilized rows was 8 percent less that that of corn planted 3.75 in. off the center of the rows. This was a result of the reduced plant population. In 2008, corn planted 3.75 in. off the center of the strip-tilled fertilized rows had the highest plant population and the highest numerical grain yield. In 2009, when the strip-till operation was performed 2.5 months before planting and there was plenty of time for the strip-tilled seedbed to settle and become firm, there were no differences in plant population and no differences in yield between planting directly on the strip-tilled rows and planting 3.75 in. off the rows.

Conclusions
Planting corn directly on top of freshly tilled strip-tilled fertilized rows negatively impacted yield. Planting at distances greater than 3.75 in. from strip-tilled fertilized rows reduced early season corn growth, uptake of nutrients, and yield. Overall, the best location for planting on these fine-textured soils was within 3.75 in. of the strip-till fertilized rows and where the seedbed was firm and moist. This is most likely to ensure quick contact between corn roots and fertilizer.

The impact of planting location will vary depending on the condition of the strip-tilled fertilized seedbed and the amount of time between planting and when the strip-till fertilizer operation was performed.

Additional years testing are needed to determine if these guidelines might also apply to strip-tilled fertilized corn planted on coarse-textured soils and when higher rates of fertilizer and other sources of nitrogen are applied.