Plant Analysis Are You Using It And Interpreting The Results Correctly?

 

Over the last two weeks I have received several calls/emails regarding interpretation of plant analysis results. In all situations, the agronomist asked how it was possible for corn plant sample results to come back saying that many nutrients were deficient or would be responsive to added fertilizer. One specific example had optimum or better soil test levels and a spring application 14,000 gal/a of dairy manure. Kind of hard to believe that V5 corn would be limited by N, P, S, Ca, Zn, B, and Mn in this situation. Lab results had been interpreted using guidance developed by an ag inputs company. I evaluated the lab results using the UW plant analysis interpretation guidelines. The agronomist and I were not certain how tall the plant was when sampled or what plant part was sampled (a third party agronomist sampled the field). Nitrogen and P were borderline deficient assuming that the plant was 12” tall or smaller and the whole plant was sampled. If the plant was more than 12” tall and the youngest leaf with collar exposed was sampled, then all nutrients were sufficient. A very different interpretation using UW plant analysis guidelines. The agronomist collected another tissue sample when the crop was at V7 and sent it to a lab that uses UW plant analysis interpretation guidelines. The crop was sufficient or high for all nutrients. I plan to follow up on this field after harvest.

 

Because there have been so many questions recently about plant analysis, I think it’s important to reiterate a few key points on the use the plant analysis. I will also provide the sufficiency ranges that UW uses to interpret tissue test results for corn, soybean, wheat and alfalfa. Before I get to that, I’d like direct your attention to a newsletter article published last week by soil fertility specialists at University of Arkansas. The article is titled “Research lacking to back claims for foliar-applied fertilizers”. This is a well written article that is very applicable to Wisconsin. You can read the full text here: http://www.arkansas-crops.com/2016/06/23/research-applied-fertilizers/