Corn plants requires a range of nutrients to develop normally and produce a high yielding and high quality crop. Yearly, soil test values provide valuable information on available nutrients and what may be needed to meet the crop demands of a yield goal. Plant analysis is an excellent in-season tool that can provide insight on how well the crop is using available nutrients. It can be very useful managing secondary and micronutrients which may be less accurate in soil test analyses. A plant analysis is simply a laboratory procedure used to determine the concentration of nutrients present in plant tissue. The information obtained from this procedure is useful in determining the overall nutrient status of a plant, thereby, allowing a grower to diagnose a suspected nutrient deficiency or detect a nutrient imbalance (deficient or excessive) before severe damage occurs. Growers, county Extension agents, consultants, industry agronomist, and University specialist can use this information to determine the cause of problems (or potential problems) or guide them to a better decision on opportunities to improve yield performance. This analysis can be conducted any time during the life of the crop but is most valuable when used early in the growing season when it is advantageous for a response to any corrective action.
What are the steps in a good plant analysis? There are four basic steps and all are important: 1) sampling, 2) analysis, 3) interpretation, 4) recommendation/data use. In corn production, UGA provides some guidelines for sampling and interpretation purposes (see the url at the end of this article). Appropriate sampling is very important at different stages of corn growth. When plants are 12” inches or less, remove the whole plants by cutting it 1 inch above the soil. Once plants are larger and just prior to tasseling, select and remove the leaf below the whorl with the uppermost leaf having a collar. After tasseling, select the ear leaf (primarily before brown silks) for analysis. Some growers and labs suggest using not only the ear leaf but the leaf opposite of the ear. If you use both, I suggest keeping them separate for comparison purposes. This data can be used to monitor the nutrient status of your crop through maturity. While it may be expensive, I have always said that beginning at V-3/V-4, a weekly sampling is very important and the data is useful in understanding how the environment and growth stage affects uptake and use. Keeping records over the years will help you be a better producer of corn. If you do keep records, I would record the growing degree day units when you sample and the stage of growth and enter that into your records. The more you study, the more you learn.
I suggest collecting 15 to 20 plants or leaves to get a good representation of the field or area of interest. Do not sample plants that are diseased, or damaged or subjected to severe stress. If you are trying to trouble shoot a problem, it is wise to take a soil sample of the area as well. In Georgia, I encourage you to wash your tissue to remove dust, dirt and other materials and allow the sample to dry and wilt. Place the samples in paper bags prior to shipping.
Plant analysis generally consists of a determination of the concentration of: nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), calcium (Ca), sulfur (S), manganese (Mn), boron (B), copper (Cu), iron (Fe), and zinc (Zn) in your samples. Prior to sending your samples, check to make sure the nutrient(s) you desire are covered under the routine analysis. If not, then a special request may need to be made. The analysis is interpreted by comparing the concentration found to known standards for the plant part and stage of growth when sampled. A sufficiency range is simply the range of concentrations normally found (through research) in healthy productive plants. Unfortunately, I have found some labs that use sample surveys to provide data on sufficiency ranges.
Please bear in mind that any plant stress (drought, heat, soil compaction, saturated soils, nematodes, etc.) can have an impact on nutrient uptake and plant tissue nutrient concentrations. A low value of a nutrient in the plant does not always mean the nutrient is low in the soil and the plant will respond to fertilizer. It may be that the nutrient is present in adequate amounts in the soil, but is either not available or not being taken up by the plant for a variety of reasons. On the other extreme, levels above “sufficiency” can also indicate problems. High values might indicate over-fertilization and luxury consumption of nutrients. Information such as soil test level, soil type, fertilizer and lime applied, previous crop, drainage, and weather conditions before sampling are essential to properly evaluate the data and make a valid recommendation.
If a deficiency or imbalance is detected early enough, it can usually be corrected in time to improve yield and crop quality. In some cases, samples collected for plant analysis are taken too late to apply a corrective treatment for the sampled crop. However, this information can be effectively used to evaluate the current fertility program and to plan future lime and fertilizer programs.
The interpretation of data can be refined by some nutrients by evaluating the ratio of one nutrient to another. A common example in corn is the nitrogen to sulfur (N:S) ratio. This ratio should be maintained between 10:1 to 15:1 for good yields. I almost always see a deficiency when the range exceeds 18:1 or higher.
Combining the information obtained from a plant analysis along with that obtained from a soil test allows a grower to plan a complete and well balanced fertility program. Using plant analysis is an excellent way to monitor the plants nutrient health, monitor the impact of timely applications of nutrients through the season, and determine if nutrients are sufficient to maintain optimum yield. A plant analysis should never be substituted for a soil test, but used to determine if nutrients are present in low, adequate, or excessive amounts in the plant, and whether the proper ratio of certain nutrients exists. So yes, plant tissue analysis is an excellent decision-making tool that should be adopted by every corn farmer in Georgia.
Plant analysis services are available through private and public labs in Georgia. I encourage you to contact your county Extension agent for more information on UGA’s lab services or your favorite industry agronomist/consultant for help in interpreting your data.
An excellent resource for help with understanding plant analysis is available at:
Plant Anaylsis Handbook: https://aesl.ces.uga.edu/publications/plant/