No Till Notes - “Soil Microbe Testing”

By Mark Watson, Panhandle No-Till Educator

The first thing I want to tell you about soil microbe testing is that this type of testing is in its infancy. Dr. Ray Ward, founder of Ward Laboratories in Kearney, Nebraska, has just begun to explore this type of soil testing. It’s safe to say that Ray will be learning along with the producers who send in samples for this type of soil health testing.

Approximately one month ago I sent Dr. Ward soil samples from a neighbor’s winter wheat/summer fallow cropping rotation, our continuous no-till dry land field where we produce winter wheat, corn, and field pea in a continuous no-till system, and our irrigated no-till field where we produce winter wheat, corn, and edible beans in rotation. This field was winter wheat that was harvested last summer and then planted to a forage mixture of field pea, flax, nitro radish, and sunflower. A neighbor’s cattle then grazed this forage mixture in March.

We wanted to sample early so we could determine how much nitrogen mineralization we could expect from these soil microbes and develop a plan for fertilizer applications on our fields. This may not be the best time to sample since the microbes are not at full capacity due to cool, wet soils. We may need to sample at a later date when the microbes are more active.

What we are looking for with this type of soil microbe testing is to see if we can predict the amount of nutrient mineralization, in particular the amount of nitrogen, the soil microbe community will release which can be utilized by the crop we are growing. If we can determine the amount of soil mineralization, we can reduce the amount of commercial fertilizer we need to apply to produce the crop. The bottom line is a healthier soil will allow us to lower our production costs. 

The tests Ray is running to determine populations and diversity of the soil microbe community is called the Phospholipid Fatty Acid (PFLA) test. The PFLA test determines the amounts of bacteria, fungi, and protozoa in the soil. This is important because the bacteria and fungi are the food source for the predatory protozoa. The protozoa feed on the bacteria and fungi and excrete excess nitrogen from their prey, which becomes plant available nitrogen. If we can predict this release of excess nitrogen, we should be able to lower the amount of commercial fertilizer we need to apply for our crop.

In general, we received the results from the PFLA testing that we expected. The soil from the winter wheat/ summer fallow rotation showed a lower population of all soil microbes. The tests also revealed no predatory protozoa in the soil which would indicate little if any nutrient mineralization. The soil is dominated by bacteria with very small amounts of fungi present including Arbuscular Mycorrhizal fungi. The Arbuscular Mycorrhizal fungi are important as they attach to roots and deliver nutrients and water to the plant’s root system. This fungi develop a web colony around the plant’s roots which increases the amount of nutrients and water the plant can absorb. 

The PFLA test on our continuous no-till soils showed good levels of bacteria and fungi. The tests also found much higher levels of the Arbuscular Mycorrhizal fungi in our soils. The tests also showed a good population of the predatory protozoa necessary for higher mineralization of nutrients. 

What we don’t know from these tests is how much nutrient mineralization we can expect from these microbes. Dr. Ward is installing equipment in his lab which will run the Haney test. The Haney test was developed by Dr. Rick Haney who works at the USDA-ARS in Temple, Texas. The Haney test uses the analysis of the soil microbes to predict the amounts of nutrient mineralization that will occur.

We are waiting to hear from Dr. Ward on our results from the Haney test once the equipment is installed. These results along with the PFLA tests should give us a good indication of the nutrient release we can expect from our soil. We are expecting that healthier soils with good populations and diversities of soil microbes will lower our cost of producing the crops that we grow. Once we can accurately determine this process, healthier soils will have an economic benefit in production agriculture.