Optimization of nitrogen and phosphorus fertilizer timing and placement in coulter-based strip-till corn systems

Fertilizer management practices for nutrients like nitrogen (N), phosphorus (P), sulfur (S), and zinc (Zn) in corn production are heavily dependent on tillage system. Many long-term no-till producers, confined largely to surface fertilizer applications, struggle with nutrient stratification and potential surface P runoff or gaseous N losses shortly after broadcast nutrient applications. Strip-till systems offer alternative nutrient placement options in both fall and spring. This strip-till study focused on pre-plant, coulter-based mixing of the upper Ap soil horizon in the future corn row zones with and without simultaneous incorporation of urea ammonium nitrate (UAN) and/or a commercial granular N, P, S, and Zn fertilizer, MicroEssentials® SZ™ (MESZ). Different strip-tillage timings (fall, spring, or fall and spring) and nutrient placements (zone-banded or surface broadcast) were compared both with and without starter (N and P) fertilizer applications during the precision-guided corn planting operation. The pre-plant P rate applied with the MESZ product equaled that applied in the sub-plots with starter (67 kg P ha-1). Corn was grown in rotation with soybean for two location-years on high organic matter prairie soils with a mean soil-test P concentration of 14.9 ppm (2013) and 24.1 ppm (2014) in non-fertilized control treatments (both no-till and fall strip-till). Total N application at 202 kg ha-1 was constant for all treatments. Treatments were evaluated by measuring soil nutrient distributions, whole-plant nutrient uptake (V6, R1 earleaf, R6), and final grain yields. Soil fertility samples, collected at 3 depths (0-5, 5-10, and 10-20 cm) shortly after planting, revealed successful incorporation of MESZ in the zone-banded area, largely confined to a depth of 5 cm. Zone banding, therefore, changed the soil P stratification little, though it did mix the fertilizer with soil in that zone. Early (V6) plant growth and nutrient (N, P, and S) uptake was significantly increased with fall applied MESZ, regardless of placement, compared to a no-till (NT) check treatment, but not consistently relative to strip-tilled treatments with no MESZ. Early Zn uptake response was less consistent; only the fall zone-banded MESZ placement with no spring zone-banded UAN resulted in a consistent significant Zn uptake advantage over NT. As the season progressed, significant responses to main treatment differences diminished. Earleaf samples collected at silking revealed treatment differences only in N concentration, with slightly higher values for treatments without added MESZ. No R6-stage nutrient uptake or final grain yield differences were significant among main treatments. Spring zone banding of a 50 kg N ha-1 in the form of UAN provided no growth, nutrient or yield benefits relative to the more common sidedress UAN application at the higher N rate. Grain yields averaged 14.7 Mg ha-1 in 2013 and 15.0 Mg ha-1 in 2014. Systems with fall zone-banded MESZ produced the highest yield (0.6 Mg ha -1, 4.2%) above the NT treatment, but this advantage was not significant. The slight (0.2 Mg ha-1) yield increase for zone-banded MESZ over the broadcast MESZ placement was also not significant. However, application of starter fertilizer, regardless of main treatment effects, significantly increased both early plant growth and nutrient uptake (N, P, and S; Zn 2013 only) and final grain yield (0.1 Mg ha-1 in 2013 and 0.2 Mg ha-1 in 2014). With constant N rates for all treatments, on moderate to high fertility soils, fall zone-banding N, P, S, and Zn resulted in significantly increased early growth and nutrient uptake but non-significant final nutrient uptake and grain yield benefits compared to NT planted with no additional P, S or Zn fertilizer. Zone banding of these nutrients thus provided little immediate corn production benefit on these soils, but the potential environmental benefits, especially with fall P application, merit additional investigation