Soil microbial responses to cover crop use

Soil microbial responses to cover crop use

Summary

WORK ACTIVITIES

When I received my grant funding, I purchased an NRCS-approved Soil Quality Test Kit from Gempler’s and supplies from Woods End Laboratories to conduct the Solivita CO₂ burst tests. One day each in spring, summer, and fall, I conducted field tests at seven sites representing a continuum of predicted soil health: grazed native prairie, 8+ year no-till crop ground (with cover crops and grazing), transitioning no-till crop ground (with cover crops and grazing), and conventional crop ground. I measured soil temperature, infiltration (spring only), and soil respiration using the Dräger tube method. I also took samples for bulk density, pH, electrical conductivity, nitrates, and soil respiration using the Solvita CO₂ burst test. These tests were conducted my me, but I sent a single set of parallel samples to the K-State Extension Laboratory for a comparison of pH and nitrates. The K-State samples also allowed me to have a baseline value for soil organic matter percentage.

A NRCS EQIP grant generously covered the cost of cover crop seeding on four of the seven sample sites, freeing up a portion of the SARE funding. I used this to justify adding the K-State Extension soil sampling expense and purchasing additional Solvita tests to use with landowners and at soil conferences.

In order to introduce cattle back onto the crop ground in the study, I needed to build a quarter mile of new perimeter fence and repair a half mile of old fence. None of this was funded by the SARE grant, however the new fence provided a protected place for the high-tensile electric trunk line that would supply the temporary electric fence for the planned rotational grazing system on the crop ground. A portion of the SARE funding helped to purchase a solar charger, polywire electrical fence, reels, and step-in posts from Gallagher. Much of the winter and spring was spent learning the process of rotational grazing.

RESULTS

Initial readings of soil respiration using the Dräger tube method showed a good correlation between expected soil health and management (especially living roots and diversity). It was hoped that the CO₂ burst test would further emphasize the relationship by discounting soil moisture and temperature differences between samples. The first results, though, were disappointing, with replicates of the same sample showing greater differences than between neighboring samples. I spoke with Woods End Laboratories and suspected that my drying methods were partially to blame, and I am still perfecting a standardized method that will work in all seasons. It is possible that the Solvita Basal CO₂ test (using the same materials, but slightly different procedures) may be the best fit for measuring soil respiration under different land treatments.

It appears that soil microbial response to positive soil practices (no-till, year-round cover with living roots, and grazing) occurs quickly. Two sites that had early cover crop (red clover) growth in wheat showed greater soil respiration than neighboring sites in wheat without red clover. The wheat alone was only slightly better than a winter fallow site of the same soil type. The long-term no-till ground (with cover crops and grazing) showed greater soil respiration than the perennial pasture in the spring. Cool soil temperatures under the pasture, and more intense grazing use of the no-till ground may have been influential.

By summer, the perennial pasture had a much more active soil microbial population than the other land treatments. By contrast, the long-term no-till and conventional fields, both in soy beans, had about half of the soil respiration than the pasture, with the no-till ground slightly better.

Yields on new no-till ground are notoriously lower than their conventional counterparts, but if the soil respiration can be shown to respond positively even before yields rebound, I think producers will be encouraged to weather through the tough transition.

WORK PLAN FOR FALL 2014, SPRING 2015

Now that I have a fully functional rotational grazing system on the crop ground, I can have more control over the sample sites that should be grazed and those that should not. The addition of several automatic waterers on the native pasture will also help me manage appropriate grazing pressure on the “control” site. I have already collected the summer, 2014 samples and done the appropriate field work. I will replicate these again in the fall, after the corn crops have dried down. If possible, I will take my final round of samples in the early spring before submitting my final report. In addition to the existing tests, I plan to borrow a penetrometer from the local conservation district to better quantify the problem of hard ground that plagues the transition to no-till. I hope to use this as baseline data to track soil changes over the next ten years.

Since I wrote this proposal, Woods End Laboratories has continued to develop the Solvita products by making various web calculators available. It is easier now to convert the numeric values from the color change tabs (that respond to CO₂ concentration) into pounds of biologically available nitrogen or pounds of carbon sequestered. I will spend some time with these tools to see how they can best be used to help producers make fertilization and management decisions.

Several laboratories are now offering soil tests that evaluate soil life by functional group (gram positive bacteria, gram negative bacteria, fungi, protozoa, nemotodes, anthropods, etc.) and the ratios of these groups to each other. I am in the process of collecting samples from each of my sites to submit for this kind of test to add depth to the study.

OUTREACH

Throughout the year, I attended several formal and informal farming meetings where I was able to talk with producers about my study and the potential uses of soil respiration to monitor soil health. I also met two clinical microbiologists in my neighborhood that are interested in helping me make the leap from general soil respiration (microbial function) to microbial diversity (by functional group).

As an educational outreach, I have started an on-farm internship program through the University of Kansas Environmental Studies Program, which offers emphases on food and agriculture or soil and water. My summer intern has been involved in all aspects of the project as well as the cropping and ranching decisions that are involved in each sample site. As an extension of that program, I have been invited to speak to an Environmental Studies student group in November, 2014 about the ecological aspects of farming. I intend to make soil health and soil microbial activity a key element in that presentation.

In January, 2014 I was elected to the Douglas County, KS Conservation District Board. One of my first activities with the board was to help lead a VIP tour to introduce local politicians and decision makers to the various work of the Conservation District. One of the stops on the tour was my long-term no-till site, so I was able to talk about my study. Additionally the district has been cooperating with two other counties to promote soil health through annual meetings and field days. I expect to showcase my rotational grazing system and share the results of my study either this fall or next spring (2015) as part of a district event.

In August, I will be speaking on soil health as part of the Kansas Grazing Lands Coalition’s Tallgrass Range School. I plan to offer participants several kinds of hands-on soil experiments that they will be able to repeat on their own land. I hope to send them home with an appreciation of the abundance of life beneath the grass.