Critical micronutrient tissue test levels and filling the N-gap in Ontario soybean

Objectives:

• Establish critical leaf tissue-test levels (for sufficiency, and in the case of boron, toxicity) for boron (B), iron (Fe), manganese (Mn) and zinc (Zn) in soybean.
• Provide a uniform set of high-resolution images (suitable for digital image analysis) for leaf deficiencies of the above four micronutrients, as well as molybdenum (Mo) copper (Cu) and cobalt (Co).
• Evaluate the ability of a foliar-applied biological (Envita™, Gluconacetobacter diazotrophicus (Gd)) to compensate for reduced atmospheric nitrogen (N) fixation in soybean under drought stress.

Impacts:

• Provision of a set of high-quality photographs, all collected outdoors in a single experiment and photographed under equivalent conditions with identical equipment, will be extremely useful to soybean growers and agronomists in diagnosing micronutrient deficiencies in the field. This will be a great advance over the currently available random collections of photos of different micronutrient deficiencies in soybean.
• Verifying the sufficiency ranges (and for B, toxicity range) in leaf tissue test values for B, Mn, Fe, and Zn will help growers and agronomists to interpret these tissue tests values going forward and decide on the necessity of intervention for yield protection.
• Envita is a product whose evaluation is only just beginning in soybean. The data we collect will add to the growing base of information so that agronomists can make predictions about the likelihood of a profitable result from using this product. Unique to this project, we will also gain knowledge about Envita’s ability to help compensate specifically for reduced N-fixation under drought stress.

• If this project is successful, in future work the digital photographs of leaves with known micronutrient deficiencies will be used to attempt to develop an AI image analysis model that can be incorporated into a phone app and used to diagnose soybean micronutrient deficiencies in the field.  

Scientific Summary:

Soybean is believed to be susceptible to deficiencies of several micronutrients, and to toxic levels of B. However, because such deficiencies are relatively rare, diagnostic tools and management recommendations are poorly developed. For example, high quality photographs of deficiency symptoms of the rarest deficiencies in soybean are hard to find, and even for the more common micronutrient deficiencies, target tissue test levels are not well defined, so it is hard to know when foliar applications of micronutrients are warranted. Growers also have questions about the benefits of foliar applications of new N-fixing biological products, such as Envita^TM  from Syngenta. We know that N-fixation in root nodules can slow down during periods of low soil moisture, which can leave the crop N-starved and reduce yield potential. Can products like Envita help to fill the N gap under those conditions?

In the proposed work, we will grow soybean outdoors in the field, but instead of being rooted in natural soil, they will grow in an artificial rooting medium which will give us complete control over micronutrient availability, nodulation status, soil N, and soil moisture. In the case of micronutrients, we will use this system to acquire diagnostic photos for all of the most common micronutrient deficiencies (Mn, Fe, B, Zn, Cu, Co, Mo), and to estimate tissue test sufficiency (and for B, toxicity) levels for Mn, Fe, B and Zn. If successful, this will allow us to improve our ability to diagnose micronutrient deficiencies in soybean going forward. The extensive photo collection may also serve in the development of an AI-based app for diagnosing micronutrient deficiencies in soybean using pictures taken with a smartphone. We will use this same soilless culture system to test if foliar-applied Envita can help to relieve N-deficiency induced by drought stress during the critical reproductive stages of the soybean crop. This research will also be complimented by a series of multi-location small plot trials comparing Envita with other treatments focussed on supporting soybean N status.

External Funding Partners:

This project was funded in part by the Ontario Agri-Food Innovation Alliance, a collaboration between the Government of Ontario and the University of Guelph.

Ontario Soil and Crop Improvement Association

Syngenta