Manganese deficiency, courtesy of Purdue University.
Although much of the attention for tissue testing is focused on corn, soybeans can also benefit from proactive tissue testing. Soil tests are excellent measures for primary and secondary nutrients and are still the best way to understand fertility and make decisions about soil-applied nutrients. When it comes to micronutrients, soil testing can be more challenging, so tissue sampling is another method to measure what is happening in your bean field. Use tissue testing as a tool to help evaluate and diagnose other issues in the field. It is important to remember if a tissue test comes back low or deficient, that does not mean your soils lack the nutrient. In many cases nutrient deficiencies are weather-induced or result from other issues such as root restrictions or a pH imbalance.
The best time to sample is when blooms first appear which has already occurred in most areas. However many are still in the R1 stage so sampling can still be accomplished over the first few weeks of blooming. Make sure to sample multiple areas of the field. If the field shows troubled spots provide samples from just inside the troubled spots as well as from the better areas of a field. For soybeans, remove the newest fully mature trifoliate from at least 25 – 30 plants and remove the stems and petioles. Place the samples in a dry paper bag overnight for best results. Be sure not to select dirty samples or samples that require washing or cleaning.
Once you have received your results, compare the soil tests for the field to your tissue tests. Are there areas where tissue tests indicate an issue exists yet the soil tests indicate high levels? If so there are likely other issues impacting the field and the best place to start looking is below ground. If pH is a problem for example some micronutrients that are required in smaller amounts can be applied via foliar applications to rectify the issue.
One of the best ways to drive higher yields in soybeans is to begin to proactively diagnose issues that may be restricting yield. Utilizing soil and tissue testing together can be a good approach to help discover and overcome potential yield-limiting issues in the field.
