Tissue Testing and Spring Nitrogen Management for Wheat

Spring tissue sampling of winter wheat can be a very useful management tool. The timing of wheat sampling does not correspond to a specific growth stage though. The important factor when determining the appropriate time to sample wheat is that the wheat has broken dormancy and is actively growing again. Generally, wheat will be at a growth stage of Feekes 3 or 4 when this occurs. The appropriate method for collecting wheat samples at this stage is to collect 25 or more whole plants from ½ inch above the soil surface. One of the benefits of early season wheat sampling is to fine tune a “green-up” nitrogen application based on the nitrogen content of the plant at Feekes 5 (please visit the Purdue Extension News Release for more information). 

Soil testing for nitrate and ammonium can also help determine an appropriate rate of nitrogen to apply, especially in a situation where manure has been applied in the last several months. Samples should be collected to a depth of 12 inches with a minimum of 10 cores representing an area no larger than 20 acres. Once you receive your results, you can estimate the available nitrogen by adding the ppm of nitrate and ppm of ammonium and multiplying it by 4 to approximate how many pounds of nitrogen per acre are currently there. Keep in mind that nitrate and ammonium testing is a snapshot in time and can vary with the soil moisture and temperature. So, you should collect the sample as close to your planned application time as possible.

Once the plants reach Feekes 6 and beyond, indicated by stem elongation and jointing, only the most recent fully developed leaf should be sampled. The most recent fully developed leaf is the highest leaf on the plant with a fully developed collar. Once the plant begins heading (Feekes 10 and beyond), the flag leaf should be sampled. Generally, 40 to 50 leaves should be sampled at these growth stages.

Accurate plant tissue testing begins with proper sample collection and handling. Make sure to collect the proper plant part for the current growth stage of the crop and collect the proper number to make the sample. Always avoid soil contamination in your plant samples. Package samples in paper bags. If shipping is delayed, allow the sample to air dry, do not freeze. Never include roots with a plant sample. If you have any questions on proper plant tissue sampling, please contact the lab for assistance.