By Dan Kaiser, Extension nutrient management specialist
Tissue sampling is in full swing and if you are taking samples there are a few things to consider for specific crops. As we progress later into the growing season, tissue sampling can be very diagnostic for some nutrients while there isn’t very good data on sufficient nutrient concentrations for others. Accurate information is crucial to ensure any decisions you make. Remember that some of what you are finding now may be too late for the current crop but should be followed up later with soil tests to determine if a nutrient is deficient and to help identify the best course of action for the following crop.
Corn is best sampled up to the R1 or R2 (50% brown silk) growth stage. The suggested sampling is a leaf sample. Minnesota suggests sampling the leaf opposite and below the ear. However, some labs may want the ear leaf or the leaf associated with the primary ear. I have also had conversations with consultants who have been sampling the uppermost leaf of the plant to look at immobile nutrients such as sulfur. It is important to remember that sufficiency levels are associated with a specific plant tissue sampled at a specific growth stage. If you are sampling a non-standard leaf, make sure your lab knows this to ensure the data you are receiving is representative of the sample collected.
For soybean, we do not recommend sampling past the R2 (full flower) growth stage. If you are finding pods on the plant on the lower nodes, then you are past the R2 stage. As plants age they tend to pull nutrients out of the leaves which results in consistently low nutrient concentrations. If you are collecting soybean trifoliate samples and are sampling at R3 or later, it is best to take comparative samples from areas with differences in growth, but have the same variety, if you notice something off in your field. Sampling a good, marginal, and bad area of the field is a good idea in order to allow you to compare results and help make a determination of what might be wrong. When sampling soybean, we suggest sampling the uppermost fully-developed trifoliate, but check with your lab first regarding whether to include the petiole with the trifoliate leaflets when you send your samples.
Most recommendations for sugarbeet sampling involve sampling the uppermost fully-developed leaf 50-80 days after planting. A study funded by the Sugarbeet Research and Education Board of Minnesota and North Dakota that concluded last year found that nutrient concentrations in the sugarbeet leaf and petiole decreased substantial between 50-80 days after planting. I would not suggest sampling much beyond a 50-60 day window after planting. Remember that some of the Cercospora treatments contain copper and may contain other micronutrients that will result in very high concentrations in the leaf tissue if samples are collected soon after treatment.
For wheat, we are really past the window for sampling in most areas of the state. There is some information on adequate nutrient concentrations for whole plant samples taken early in the growing season and flag leaf samples collected at anthesis.
Remember that having a second source of information is important when interpreting tissue sampling results. Sufficiency ranges may or may not be accurate and may vary from variety to variety, making interpretation of tissue sampling results difficult.