On our farm we sampled five fields for biological activity this fall. We waited to sample the fields until the middle of September. The reason we waited was to get some rain so we could get our probe in the ground. We also figured moisture may increase the amount of biological activity.

The fields we sampled were wheat stubble from this year’s wheat harvest and field pea stubble from this year’s field pea harvest. We also sampled a field of dryland corn, and a field of cover crops that was planted where we weren’t able to plant dryland corn due to wet conditions in the spring. The cover crop was planted in the middle of July.

The cover crop consisted of sunflower, open-pollinated milo and a few field peas. Finally, we sampled a forage crop, which was planted following our harvest of irrigated winter wheat. For our forage crop we planted oats, forage radish and red clover. The forage crop was planted around Aug. 10. We did apply 0.75 of an inch of irrigation early in the forage crop’s growth.

The results of these samples were pretty interesting. Ward Laboratories in Kearney, Neb., ran these tests for us. They used the Phospholipid Fatty Acid (PFLA) testing. As expected, the winter wheat stubble where very little was growing in the field showed the least amount of soil microbial activity. The total living microbial biomass was 1,248.84 nanograms per gram. The functional group diversity index was 1.134. Each of these figures was given a slightly below average rating.

This sample was also dominated by bacteria, which made up 52.32% of the total biomass. The total fungi were 2.05% of the biomass with no arbuscular mcorrhizal fungi. All the fungi consisted of saprophytes. The sample also indicated no protozoa, which are the predators of bacteria. Without predators of bacteria, there is very little potential for mineralization of nutrients.

The dryland corn showed considerably higher biological activity with a total living microbial biomass of 2,302.78 nanograms per gram, which is an average rating. The functional group diversity index was 1.58 with a rating of very good. The bacteria biomass rating was much higher compared to the wheat stubble, but made up a smaller percentage of the total biomass at 44.25%. 

The total fungi percentage was much higher at 10.39%. Of the fungi, 1.82% was arbuscular mycorrhizal and 8.57% were saprophytes. There was also 1.33% protozoa present. This gives a predator-prey ratio of 0.0302, which is in the excellent rating range. This would indicate that the soil has a high potential for nutrient mineralization and the release of these nutrients for the plants.

The cover crop consisting of open-pollinated milo, sunflower, and field pea showed slightly higher total living microbial biomass than the dryland corn with a 2,517.72 nanograms per gram. I would guess that having the somewhat diverse mixture may attribute to the higher number. The functional group diversity index was slightly lower at 1.464. 

Both numbers rated in the slightly above average to good category. The total fungi were higher at 12.18% of the total biomass with 1.92% arbuscular mycorrhizal and 10.26% saprophytes. The protozoa number was lower than the dryland corn at 0.71% of the total biomass. This gave a predator-prey ratio of .0149, which is in the good rating, but would indicate less mineralization of nutrients than the dryland corn sample.

Next week we’ll look at the two samples that surprised me.

Part One  Part Two Part Three Part Four