Want to Try One of the New Microbials? Thoughts and Considerations

Soil microbes through the lens of a microscope.

You’re going to try one of the newer microbe products. I’m going to share some considerations so that you get the most information out of your first look at the product you have chosen – I’m not going to try and talk you out of using the product. I am going to propose an on-farm comparison. And I’m going to suggest some additional considerations you might make that give a new product containing living organisms the best possible chance to be of benefit to you.

The On-Farm Comparison

Plan your two-treatment (no product versus product) comparison well in advance. This comparison will take time out of your production schedule, so good planning reduces the hassle factor. I recommend you use the split-field approach, where you split each field for the untreated versus treated comparison rather than splitting treatments by applying them to separate whole fields. Whole fields, even those that share a fence row/field boundary, are never the same (different management histories, different proportions of the different soil types in the fields) and can badly confound interpretation of the comparison. If you can, split the field along a line that cuts across the different areas in the field and best captures all the production environments in the field.

In all other ways manage the field the same, as a whole singular unit. I don’t care what the product label says, don’t change the nitrogen (N) rate, the seeding rate, or the weed control protocol. Changing any other management practice confounds the interpretation of the comparison. If the label indicates that the N rate can be reduced by 40 lb N/acre when you use the product, then drop the N rate by that amount across the whole field (you’ll be better able to see the benefit of the product).

When taking samples or data (soil samples, plant tissue samples, root digs, grain yield, etc.), remember that the most similar areas in your comparison lie close to each other, on either side of the dividing line. No field is exactly the same in all of both halves on each side of the split. So don’t take data from the whole of each half – take samples/data close to the dividing line, along the whole length, where field/soil conditions are most similar and only your treatments should cause a difference. At harvest, take the yield on each side of the dividing line, along the whole length (actually weigh the grain if you can). A yield monitor can be used to see if there were particular areas/soils where the product did or did not work, but the return on investment to the treatment needs to account for the fact that the product was applied along the entire length of the split.

Additional General Considerations

Some products contain only one organism or one class of organisms with similar requirements. Other products contain a diverse range of organisms. Application methods and timings might differ because of this, so read the label carefully. There is often more than one way to apply these living organism formulations. Always follow label instructions, but either seed treatment or in-furrow application, if among recommended options, will likely optimize crop root - product contact.

Carriers can be dry (e.g., peat or clay) but water-based carrier recommendations are common. Many products are sold in water-based formulations which are further diluted prior to application. The liquid materials used to ex- tend/dilute the microbe product need to be managed so as to minimize any possibility of killing the microbes. Spray water should not be salty or sulfurous. Even when well supported on the microbe product label, don’t let one of these living organism materials set very long when mixed with liquid fertilizer (all are salty to some ex-tent) or pesticides. Generally speaking, once the microbe product is mixed with an extender/diluent, it needs to be used soon (that day). Some microbes may be sensitive to certain micronutrients like boron (B), zinc (Zn) or molybdenum (Mo) that are sometimes found with in-furrow or foliar fertilizer formulations, so avoid mixtures that involve these. Always jar test any product mix/formulation that is not well supported on the microbe product label.

When spray applying one of these living microbe products, you can avoid shear forces that might kill a portion of the organisms at the nozzle screen by using lower spray pressures and larger screen sizes. Some microbe product labels recommend soil application, usually to get greater coverage of the growing root system. Time the application according to the label recommendation, especially considering that larger plants will intercept more of the product if a broadcast spray application is made. With a ground/soil applied product use plenty of water. Probably needs to be drenched/watered into, not onto, the soil surface. Sunlight, especially ultraviolet light, is often harmful to microbial organisms. Sunlight warms the surface, raising temperatures and causing water to evaporate. This dries out the surface and desiccates microbes. Ultraviolet light can kill microbes directly, effectively sterilizing the surface. With foliar applied microbe products, read the label carefully – you might be better off making the application later in the afternoon when the ultraviolet light duration between application and evening dark will be shorter. Might give added microbes more time/better conditions to establish on foliage surfaces.

We in production agriculture are going to be working with these new microbe products for the foreseeable future. To better understand their potential to improve soil productivity on our fields and farms we need to evaluate them using ‘best practices’ for the on-farm research and with general consideration of the needs of these living organisms.