Wheat producers in South Dakota always strive to grow a premium product. Quality in wheat often depends on test weight and protein content. Protein premiums and penalties in wheat have increased interest among wheat growers in producing a product that meets or exceeds market standards (standard protein is 12% for hard winter wheat).
Factors to Consider
It is possible for producers to manage winter wheat for protein content. Several factors affect protein content in wheat including genetics, timing, precipitation, temperature and heat during the growing season. In addition soil nitrogen levels, source, amount and timing of nitrogen fertilizers play a role.
The primary building block or component of protein is nitrogen. Therefore, a lack of nitrogen available to wheat can limit yield and/or result in low-protein wheat. Typically, wheat will use the available nitrogen to satisfy yield potential before it uses nitrogen to produce protein. Therefore, in environments where yield is not limited by moisture or heat, protein content could be negatively affected by a lack of additional available nitrogen to satisfy the plants requirements.
Timing Fertilizer Applications
Fertilizer management for high-protein wheat can be tricky. Applying all of the nitrogen at seeding, especially in winter wheat, could result in nitrogen losses under certain environmental conditions or unnecessary expense if the season becomes hot and dry. Similarly, high levels of nitrogen available to winter wheat in the fall under favorable growing conditions could result in excessive tillering, delayed maturity and lodging. The wheat plants often have to abort tillers as temperatures rise in the summer and moisture becomes limiting. Nitrogen used to produce aborted tillers is then not available to support yield or protein.
Nitrogen uptake in winter wheat is highest in the spring between March and May. Producers can opt to apply a substantial portion of their nitrogen to their winter wheat in the spring. Applying fertilizer in the spring allows the grower to base his yield potential on mid-season growing conditions and crop potential. However, fertilizer should not be applied on top of snow and, depending on the form used, additional moisture will be required after the application to ensure the fertilizer is moved into the soil.
Some producers have the option to apply fertilizer in a mid-row band at seeding. This system has a number of benefits. Producers can apply enough fertilizer at seeding to allow the crop to meet a conservative yield goal. The nitrogen is not available to the wheat seedlings until spring when roots reach the fertilizer band. This should prevent the wheat from setting excessive tillers in the fall. The fertilizer is placed in the ground which protects it from potential losses due to volatization. The nitrogen is available to the wheat in the spring when N uptake in winter wheat increases rapidly and adverse weather can prevent spring fertilizer applications.
Adding Additional Nitrogen
In a year when environmental conditions are conducive to high wheat yields, growers still have the option to add additional nitrogen if they think yield may exceed the original yield goal. Nitrogen additions up until growth stage Feekes 5 (end of tillering) can support yield. Nitrogen additions made at Feekes 6 (jointing) or later will impact kernel set, size and protein.
In situations where wheat has a high yield potential it is important to remember that wheat will use available nitrogen to satisfy yield first and then convert nitrogen to protein. Low protein wheat is produced when nitrogen availability matches yields but is insufficient to produce acceptable protein. In most situations where nitrogen is limiting, additional applications made at Feekes 6 or later can help bump protein. Nitrogen applications should be based on soil tests and fertilizer recommendations.