Corn response to sidedress nitrogen
Dry weather in many parts of the state may affect recent applications of sidedress nitrogen. In addition, the growth stage of the corn crop at the time of application is a factor in nitrogen utilization. Many fields in the dry areas are in the V6 stage and the establishment of nodal roots has been slow because of the hot and dry conditions in the top couple inches of the soil.
Fertilizer nitrogen either exists in the nitrate or ammonium form. The plant may utilize either form but the nitrate forms moves with water and ammonium form must be in close contact with roots for uptake. Since sidedress occurs in the middle of the row, either nitrate moves with the water being taken up by the roots or roots have to grow into the area of the nitrogen deposition. Under dry conditions movement of nitrogen by water is limited and root growth is restricted. Until a significant rain event (at least a ½ inch rain), sidedress nitrogen may be not utilized by the crop.
During extended dry periods producers may see some advantage to anhydrous ammonia versus UAN-28%. The vapor movement of the anhydrous will expand into a greater area between the rows where the 28% band will have to wait for rain to move more into the soil profile. As a result, roots may reach the anhydrous band sooner than the UAN band. This generally occurs in years that short supply of rain reduces yield potential.
Corn that has received starter nitrogen may also look better under dry conditions. The first three to four weeks of the crop, the seed generally provides adequate nourishment until the nodal root system takes over around the V5 to V6 growth stage. At this time the nodal roots should be established enough to draw nutrients from the soil. Plants that have starter will be able to reach nitrogen sooner, which becomes important when weather events, such as dry weather, reduce nodal root development.
The use of foliar fertilizers will not be adequate to correct limited nitrogen uptake from dry soil conditions and would be considered a poor input choice. Even under good conditions, university research has shown little benefit to foliar fertilizer applications in Ohio.