Fall nitrogen recommendations for winter wheat
Fall-seeded wheat generally does not require N fertilizer for establishment. Fall-applied N or preplant N can aid in the establishment of wheat under specific planting conditions and crop rotations, but should be managed on a case-by-case basis.
Previous research has suggested the need for fall-applied N to help compensate for the large amount of crop residues produced by corn and grain sorghum, but recent data indicates that this added N may not be as beneficial as once thought and can potentially promote disease and lodging pressures later in the growing season. Incorporation of a large amount of crop residue from a summer grain crop may lead to immobilization of residual soil N. For crops other than flood-irrigated rice, fall-applied N has shown little or no benefit on wheat yield when late-winter-applied N is properly managed.
Preplant or fall-applied N can increase biomass and aesthetics of wheat following summer grain crops, but has little influence on final wheat yields under well-established, properly-managed production practices. There is usually adequate inorganic N available in the soil for wheat following well-fertilized corn and grain sorghum crops. The University of Arkansas Division of Agriculture recommends fall-applied N only when winter wheat follows flood-irrigated rice in the crop rotation.
Information on the need for fall-applied N following furrow-irrigated (no flooded) rice is not available, but is probably similar (no major benefit) to wheat following corn or grain sorghum. Wheat growth following flood-irrigated rice is usually poor for several reasons. First, following flood removal previously flooded soils tend to have low amounts (< 10 ppm) of inorganic N present. The large amount of rice straw and roots (even following burning) that is produced by rice may also immobilize soil inorganic-N for an extended period. \
Finally, the anaerobic conditions created by flooding limit P availability too and inhibit vigorous wheat growth in the absence of proper fertilization and straw management. The combined effect of the low N and P availability is visually evident when the paddy area (poor growth) in the field is compared to the area where the rice levees (vigorous growth) had been located. Thus, it is recommended that 40 to 50 lb N per acre be applied in the fall when wheat immediately follows rice in the rotation sequence.
Other considerations for preplant or fall-applied N based on planting date and grazing for grain are listed below.