Troubleshooting Problems with Plant Analysis
A green growing crop is a delightful sight, and it is used by many people as an indicator of crop nutrient status. If you have fields with some yellow areas or slow growth, these symptoms may indicate a nutrient deficiency. Most commonly, yellow-looking plants may be deficient in nitrogen, sulfur, or both. If detected early, there may still be time for rescue treatment.
Plant analysis is not a magic or foolproof tool, but it can provide useful information in diagnosing problems when combined with soil analysis and good field scouting. During the summer, our technical staff receives many questions from agronomists, crop consultants, and farmers on troubleshooting problems in their fields. The following tips and tricks will help you identify potential nutrient deficiencies early.
Troubleshooting nutrient deficiencies based on visual symptoms can be difficult if symptoms look similar (yellow for nitrogen and sulfur deficiency in the early season) or indistinct (slow growth for phosphorus deficiency). Proper troubleshooting requires you to collect paired plant and soil samples from the area with poor plant growth and an adjacent area with good plant growth. A single plant sample from the poor area is seldom enough information to accurately identify the nutrient deficiency. A soil sample from the same area is needed to determine if the soil nutrient supply is truly lacking or if reduced plant nutrient uptake is caused by another factor (e.g., soil saturation, soil compaction, cool temperature, disease).
With paired plant and soil samples from both good and bad areas, you can compare the results and determine if the symptoms are caused by one or more nutrients or non-soil issues. This comparison is particularly important for secondary and micronutrients that may also reduce plant uptake of other nutrients such as nitrogen, which could otherwise misidentify the deficiency and lead to the wrong corrective treatment (a common problem when only one plant sample is collected). Plant and soil samples should be collected within 7-10 days of symptom development to identify the nutrient deficiency and to have enough time for a rescue fertilizer application if possible. Plant samples collected after this window may be suspect as other issues may develop and confound the results.
The picture below shows patchy yellowing in a spring wheat field during tillering stage. Plant and soil samples (good and bad) determined that sulfur was deficient in yellow areas, and the grower still had options for applying sulfur fertilizer to correct the deficiency. This is a great example of paired plant and soil analysis helping the farmer choose the right corrective action, rather than blindly putting more nitrogen on yellow wheat.
Yellow wheat showing potential sulfur deficiency (upper leaves yellowing first), but there might be soil nitrogen losses too. A paired plant and soil sample is the best way to decide the right corrective action.
Collecting plant and soil samples for troubleshooting nutrient deficiencies:
- Collect one plant sample in the area with possible nutrient deficiency symptoms (bad) and one plant sample in an adjacent area (~50 feet) into the crop that looks normal (good). Collect the correct plant part for that plant growth stage (see instructions on plant sample bag or plant sampling guide).
- Collect one soil sample (0-6 inch) from each location where you collected the “good” and “bad” plant samples.
- Take photographs of individual plants that show distinct leaf symptoms (not landscape photographs) from each location where you collected the “good” and “bad” plant samples. Keep these photographs for your records; these will help in interpretation of plant analysis results.
- Submit plant and soil samples for Complete Nutrient Analysis (also called Option F for soil samples).
If you have fields with areas of poor plant growth, now is the time to collect plant and soil samples to determine if a nutrient deficiency is the issue. The troubleshooting procedure outlined above will help you detect nutrient deficiencies early and decide upon the proper corrective action if needed. To learn more about proper plant and soil sample collection and interpreting reports, please see the resources below.
Plant Analysis Guides
Plant Sampling Guide
Interpreting Plant Analysis Reports
Soil Analysis Guides
Soil Sampling Guide
Interpreting Soil Test Reports