On-Farm Evaluation of Fluid Starter Potassium Fertilization for Corn Using Precision Agriculture Technologies.

Use of fixed fluid N-P-K starter mixtures in most field studies precludes firm conclusions about specific starter K effects on corn. This study evaluated corn early growth, early plant K concentration and uptake, and grain yield responses to fluid starter K fertilizer. Eight trials were conducted in 2007 and 2008 at Iowa farmers’ fields using a strip trial methodology, global positioning systems (GPS), yield monitors, and geographical information systems. Seven sites were managed with chisel-plow tillage and one with no-tillage. Soil-test K was measured using a dense grid sampling approach (0.5-to 1-ha cells). Treatments replicated three times were a non-fertilized control, commercial fluid K₂CO₃ starter (0-0-25 N-P-K) applied to the furrow at 22 kg K₂O ha^-1, broadcast K at 134 kg K₂O ha^-1, and broadcast K plus starter K. The broadcast K rate is commonly applied by farmers before corn for corn-soybean rotations. Treatment averages along the strips showed that K fertilization did not affect early plant dry weight consistently but increased early K concentration and grain yield at four sites. However, sites with early K concentration or uptake responses seldom coincided with yield responsive sites. Starter K in addition to broadcast K did not increase yield further at any site. Soil-test K and crop responses varied greatly within fields, and responses differed for field areas with different soil series and soil-test K values. The differences usually were explained by the mean soil-test K level of the zones and seldom by soil series or topography or could not be explained with the methods used. We conclude that starter K increased corn yield in low-testing soils but seldom in high-testing soils or when it was applied in addition to broadcast K rates commonly applied by Iowa farmers.