Comparing Measurable Indicators of Soil Health under Two Different Forage Harvesting Methods Four times During the Growing Season

Comparing Measurable Indicators of Soil Health under Two Different Forage Harvesting Methods Four times During the Growing Season

Summary

Description:

Log Cabin Livestock is a 640 A. un-incorporated family owned stocker cattle and sheep farm located in the central Upper Peninsula of Michigan. Owned and run by Ben and Denise Bartlett since 1981, it produces approximately 200 head of Holstein stocker steers which are purchased in the late winter and spring and marketed as heavy feeders in the fall of the same year.   It also produces about 600 lambs which are born in May from 375 ewes and weaned in September. Approximately 500 lambs are marketed as feeder lambs in November or December and the remainder are kept as replacement ewe lambs. Log Cabin Livestock considers itself a “grass farm” as we rely on our ability to harvest solar energy as grass growth throughout our summer season, which runs from mid-May to late October or early November. Our grass is harvested via planned grazing for our ewes and lambs as well as our stocker cattle throughout the growing season. We graze each paddock at least twice and up to 4 times per year alternating between the flock of sheep and the herd of cattle as much as possible to diversify grazing pressure and as part of our of parasite management program. The ewe flock uses the mechanically harvested forage throughout the winter. Of the 640 acres owned, approximately 350 acres are in improved and un- improved pastures with the remaining acres managed as timber and wetlands. We also rent approximately 350 acres which we use primarily for hay or haylage and some grazing.  

Ben brings a background of 30 + years in Cooperative Extension as a regional livestock educator to this project. He has been active in promoting planned grazing, effective forage harvesting, livestock management and low-stress animal handling throughout his career. As a retired extension educator, he now has more time to explore new knowledge applied to forage production that has the potential to impact many North Central Region livestock producers. Denise, is a retired K-12 teacher with years of hands-on farming experience and also brings an interest in learning and sharing what they discover with their fellow farmers.

Previous Sustainable practices:

We have practiced a “controlled grazing” program to optimize forage productivity almost as long as we have had livestock. Our first attempts at improved grazing management were done with temporary fencing (that’s all the fencing we had) and was full of mistakes (learning experiences) like grazing too short. We quickly saw the benefit of “rotating” the stock from paddock to paddock but are still learning all the nuances of getting this right for the stock, the forage, us, and now, in addition, the soil health. The core program of grazing is supplemented with species rotation to manage internal parasite load as much as possible and use of manures and compost for field fertility, again, as much as possible with de-wormers and chemical fertilizers used on distance fields.

Project Description

Goals: To compare various soil health measurements after two animal species were grazed over four different seasonal harvest periods. Or stated another way -  “Does when we graze (stage of plant maturity and time of year) impact soil health in ways that can be measured?” Dr Lee Manske, North Dakota State University, teaches in his two day grazing short course that on western North Dakota rangeland, that grazing 1/3 of pasture plants between the 3-leaf and flowering stage of maturity will have a beneficial impact on soil health resulting in increased fertility and increased plant growth. My hope was to identify measurements that could demonstrate this positive soil health impact with our cool season forages on forest soils.

Process: There is a lot of “generally accepted” information that some kind of rotational or management intensive grazing is superior to set stock grazing. It is also generally accepted that grazing can be “good” for soil health if there are always living roots in the soil and there is no tillage. However, while there is a recent avalanche of information about cover crops on tilled soil and their benefit, there is limited information, especially in the eastern side of the NC SARE region, of how differences in grazing management could impact soil health. In addition, how, in a relatively short period of time, over a grazing season of 1 to 2 seasons, can we measure changes in soil health? The most familiar monitoring tools, measuring soil organic matter or counting angle worms, could take many years to see a change or is subject to a great deal of chance and variability. Dr. Manske’s work stimulated the ideas that soil health and grazing management were not just parallel events but an interrelated system where the “right?” grazing management would improve soil health which in turn would improve forage productivity. The main two forage limiting factors are water and fertility and improved soil health could enhance soil fertility and with increased carbon and increased water holding capacity.

Since our farm is a small commercial venture it would not be possible to research all the factors involved in grazing management and soil health and therefore we decided to focus on two issues: Were there some “soil tests” or indicators that could identify changes in soil health within a grazing season and would the timing of our grazing (plant maturity and time of year) impact these measures of change in soil health. We hoped to generate enough information to support in general the idea that our grazing management can impact our soil’s health, provide some clues on how to manage our grazing, and ideally, generate some interest in future grazing management – soil health – forage productivity research study.

Project design: This project will be limited to comparing various grazing times (4 times over the grazing season) and how it impacts various measurable soil health/life indicators. We have added a clipped sample to our project since we wanted to compare how grazing versus hay harvesting impacted soil life as mechanical harvesting is a common practice in this region.  

The trial utilized stocker steers and ewes and lambs to graze a paddock in which an exclosure was erected prior to the turn in of animals. The grazing stock were grazed in the paddock for one to two day duration to remove approximately 33% of the forage and then moved on to their respective next paddock. The day the animals were moved out, half of the exclosure forage was clipped to simulate hay harvesting, the other half of the exclosure was left standing as a control plot. Pre and post grazing and clipping forage samples were collected for quantity and quality analysis. Seven days post grazing, three replications were identified in each of the control, clipped, and grazed areas. 15 soil samples were taken from each replication; the grazed paddock, the mechanically harvested plot and the control plot. We sent soil samples to Ward Labs in Nebraska for Haney analysis including: a sample from each replication – 3 from grazing, 3 from clipping and 3 from control for Haney tests and then a composite of those 3 samples of each treatment for a PLFA test, 1 from the control and 1 each from the two treatments.   This sampling procedure was performed four times during the growing season, in both cattle and sheep grazed paddocks: Early (first) Grazing (prior to flowering), Late (first) Grazing (after the seed head formation), at the Second Grazing of the paddock (approximately 45 days after the 1^st grazing), and in the Fall (sampling immature grass, but after September 1).

While it would have been very interesting to see if plant maturity time of grazing impacted future forage growth, the complexity of that trial to generate solid information was beyond the capacity of a farmer directed trial at this time.

People:

This project is the refined version of this concept that we started in 2013. After hearing Dr. Jill Clapperton, soil health consultant – Montana, speak about soil health and attending Dr. Lee Manske’s grazing school, we did a small grazing – soil health project the summer of 2013. The 2013 project was self-funded, small scale, and helped us identify some of the elements that needed to be part of this project. It was obvious we needed some assistance in interpreting the soil health results and while we included services of Dr. Clapperton in our grant, we experienced limited success in getting timely replies from Dr. Clapperton. We feel she is a great resource but maybe not the right person for relating grazing to soil health issues. We did discuss our project with Ward Laboratories and decided to work with both Dr. Ward and Lance Gunderson of Ward Labs. In addition, we have been in contact with Dr. Manske and his associates and have reviewed our findings with them.

Results:

The goals of this project, in summary, were to demonstrate that grazing immature pastures would stimulate more soil life activity than grazing mature pastures. In addition, it was hoped that we could identify the soil tests that best showed this finding. We also did summer/2^nd grazing and fall grazing tests to monitor what was happening to soil health over the entire grazing season. This was accomplished with our herd of 160 stocker steers and 350 ewes with 600 lambs by side during our regular planned grazing program. The paddocks chosen for testing were fields we felt were “typical” of our operation, were as uniform as possible, were not near fence lines, water points or trees and would be close to the grazing stock.

Discussion of the “early” and “late” 1^st grazing:

The stock were grazed with the goal of removing 25 ~ 33% of the available forage, one or two days of grazing per paddock. Three pre grazing and 3 post grazing samples were collected, hand clipped to approximately one inch level and dried to 100% dry matter on both the cattle and sheep grazing paddocks. The sheep paddock had 1735# of dry matter available on May 30, 2014 and had 1283# of residual plant material on June 1 after grazing for 26% harvest. The cattle paddock had 1250# of forage on June 1 pre-grazing and 912# of residual forage on June 2 for a 27% harvest. Feed quality analysis was also done on both pre and post grazing samples and support the idea that stock choose the “better” forage. Using crude protein as an indicator of feed quality: In the Early First Grazing treatment - pre grazing steer: 15.8% and sheep: 16.4% as compared to post grazing steer: 13.7% and sheep 14.3% crude protein levels. For the Late First Grazing – Pregrazing steer: 10.0% and sheep: 10.4% and post grazing results of steer: 8.3% and sheep 8.7% crude protein. (these are the only time the results were neat, clean, and as expected – but that’s why we do “research”, right?)

The Late Grazing forage sampling, pre grazing on 6-25 and post grazing on 6-27, demonstrated significant growth from the first grazing. While the fields were not the same but very similar, the amount of forage available in the Early Grazing was (sheep 1735# & cattle 1250#) to over 5438# in the Late Grazing, (sheep 5408# & cattle 5468#) or a gain of 3945#. That is about 158# of forage growth per day. The forage in the Late Grazing was over 3 foot tall and it was very difficult to “throw” the sample ring and get it to the soil level to collect an accurate plant sample especially after the stock had walked down much of the forage. The sheep post grazing utilization samples showed there was more forage “after” grazing than pre-grazing and the steer site only showed 8% utilization. Visually, it looked like the about 1/3 of the forage had been consumed and the stock were satisfied and full when moved to a fresh paddock.      

After the grazing stock exited the paddock, ½ the exclusion area was clipped with a windrower in three alternative strips to provide 3 replications of control, 3 clipped strips inside the exclusion area, and then 3 areas in the grazed area opposite the exclusion were selected for 15 soil samples per replication. Each site; control, clip, graze x 3 per cattle or sheep grazed was sent in for a Haney soil health analysis and a composite of the 3 soil samples per treatment and grazing species were sent in for a PLFA soil microbial community analysis. The Haney soil results were averaged for each treatment over the 3 samples per treatment.

I have limited the data reporting to those indices that I felt provide the most overall representation of the level of soil life under the 3 treatments. The inorganic nitrogen levels were noted because in conversations with Dr. Manske, he felt that if you only had one number and wanted to use a low cost test, the inorganic nitrogen could be an indicator of microbial activity.

Indices Utilized in Measuring Results:

Soil Health: represents overall health of soil system, number will be 0 ~ 50, more is better

Solvita CO2: the CO2 released in 24 hrs. - measures microbial activity, higher number is better

PLFA Biomass: est. of living microbial biomass, less 500 poor, 2000 avg, over 4,000 excellent

Inorganic Nitrogen: Nitrate + Ammonium in ppm N - via H3A extract

Discussion:

If we average the steers and sheep data - it represents 2 different grazing species and two different paddocks/fields.

Average:

The “early” graze treatment did have more PLFA biomass than the control or clipped treatments which would support the idea that grazing was stimulating more microbial activity. However, the other two measurements of soil microbial activity, soil health and solvita indicate less microbial activity. I am not sure I can explain this but a couple of considerations: We did our soil sampling 7 days after the grazing event – was this the best time to capture maximum microbial activity as the result of the grazing? And, is there is no best time because it depends on soil temperature, soil moisture, etc.? The other consideration is that the PLFA test and the solvita test results and soil health number may not represent amount of microbial activity equally, both accurate but not on the same timeline. Another consideration is that the soil health calculation is dependent on the amount of organic C and N, (C - carbon & N- Nitrogen) and an increase in microbial biomass can result in a decrease in soil organic C and N. In the “Late” data, all the numbers and especially the soil health and solvita results would indicate that grazing decreases soil microbial activity. The inorganic nitrogen test results do not demonstrate an impacts of grazing or clipping. The levels of inorganic nitrogen (PPM x 2 = #acre) were also low across all treatments for all sampling periods. Bottom line, grazing does impact soil microbial activity, probably, positively when grazing is done on immature plants (Early). The Late grazing data supports the idea that grazing does impact soil life but the results at 7 days post grazing would suggest that soil life activity is decreased.

* the sheep control PLFA biomass data was in error and a calculated number was substituted based on steer PLFA information

Discussion:

If we average the steers and sheep- it represent 2 different grazing species and two different paddocks/fields.

Average:

In both the Second and Fall grazing treatments, the grazed samples again were most often demonstrating the lowest soil life results. In this project, it seems that grazing does impact our indicators of soil life and except for the early grazing trial, grazing decreases the indicators of soil life 7 days post grazing.

Other observations from the test results:

Fungi/Bacteria ratio- more fungi is better .35 excellent

SOM – soil organic matter

Inorganic Nitrogen levels - ideally are 100 pounds per acre –peak of growing season

 I compared the fungi/bacteria ratios across all 4 harvest periods by the different treatments:

Control fungi/bacteria ratios:     steers .185, sheep .250   Average = .2175

Graze   fungi/bacteria ratios:     steers .253, sheep .285   Average = .2688

Clip       fungi/bacteria ratios:     steers .240, sheep .217   Average = .2288

I am not sure the difference is statistically different but the trend does favor the paddocks that were grazed.

I don’t expect the SOM to be influenced in one year by the treatments but it is interesting to look at the history of the paddocks and compare it to the SOM levels. The inorganic nitrogen numbers closely paralleled the SOM values.

The Early Graze sheep, SOM - 5.07; the Second Graze steers, SOM - 4.36, and the Fall Graze steers, SOM - 4.26 were all the same paddock. This paddock has been in pasture for over 30 years and has not been hayed.

The Early Graze steers, SOM - 3.86 and the Second Graze sheep, SOM -3.63 were the same paddock, pasture the last 3 years and was cut for hay the previous 20 years with minimal added fertility.

The Fall Graze sheep, is the lowest SOM, 3.53 and has only been in pasture the last 4 years and was tilled for the prior 2 years.

The Late Graze steers, SOM -4.13 and Late Graze sheep, SOM -5.0 was the same field that has always been managed as one field and was divided by temporary fence into two 4 acre paddocks for this trial. I would have expected to see very similar SOM. This was a reminder of the inherent variability in soils and the importance of replications and cautions when making conclusions.

What did I learn (so far)?  Grazing as compared to control and clipping treatments did impact indicators of soil health. Our pasture paddocks appear to have an excellent level of soil life, with peak PLFA biomass data being over 10,000ng/g. PLFA biomass data seems to be time of the year dependent, but it is not certain if that is due to plant physiology, soil temperature, or amount of daylight or a combination of factors.    

Discussion:

The primary finding in this one year, on-farm, grazing- soil health project is that soil health is a very complicated system!  While we did demonstrated that grazing did impact indicators of soil health within 7 days of treatment, the initial interpretation of the results where that in most cases the impact was to “decrease” indicators of soil health and not to increase the soil biomass, soil health index, and Solvita score.  This was contrary to our hypothesis that grazing “early” would have a more beneficial impact on soil health that late or mature plant grazing.  

We have been contacting various soil health experts:  Drs. Haney, Manske, and Ward Laboratories and unfortunately have not gotten a good explanation of why we saw the unexpected results.  The most common reply was to repeat the project for another 2 years.  We are continuing to study previous work even though some of the grazing impact on soil health/ nutrient cycling was done about 30 years ago before the current more sophisticated soil tests were available.  We are also working on finding assistance to do a statistical analysis of the results to improve the confidence of the results.

I think one of the major issues that need clarification is the need to include time in the discussion of soil health.  We are looking for those indicators that could tell us what kind of impact on soil health a single grazing event would generate. We are looking for short term impacts, changes in soil live indicators that obviously could lead to long term impacts, such as soil organic matter levels, fertility levels, etc.  Having the ability to measure the impact of a single grazing event would allow us to quantitatively measure the impact of different kinds of grazing management.  For example, what is the difference between grazing an immature plant vs a mature plant, or grazing 33% of the available forage vs 90% of the available forage, or the different between a 4 hour mob grazing event vs a 2 day less intense grazing.  

The primary information that I can share from these on farm research findings AND our literature review is that our grazing management can make a difference in soil health.  The general principals of soil health recommended to cropping programs are applicable to grazing:  Limit tillage, keep the soil covered, keep living roots in the soil, and promote plant diversity.  Continuous stocking with sever grazing does meet the goals of no tillage and living roots but the roots are often very short due to sever grazing, the ground is not covered with litter because it has been eaten, and over grazing often limits the number of surviving species in a pasture.  Our pasture with 30 years of rotational grazing history were considered “very healthy” as evidenced by high levels  of PLFA soil biomass  and soil organic matter levels of 3.5% to over 5%. The second “finding” would be that soil beneath our pasture plants is a very complicated living system.  What we do with our grazing management does impact this living system and we need to utilize what we do know about “good grazing”; take half- leave half, allow adequate recovery time, maintain a diversity of plants, and more fully appreciate the value of “improved soil health”.    A third “finding” is the need to more fully understand what impacts our grazing management has on soil health resulting in future plant yields, water holding capacity, and the bottom line – grazing/pasture profitability. 

Project Impacts: See on-line survey – Inconclusive results

Outreach:

The results of this trial and literature review will be presented in an approximate one hour presentation at the Michigan Sheep Breeder’s January 4^th, 2015 annual meeting of approximately 100 people, presented twice at a the Michigan Small Farm conference on January  17, 2015 to an estimated 40 people in each session,  to 30~40 people at the Michigan Upper Peninsula Ag for Tomorrow conference on March 10 and at the Michigan Forage and Grazing meeting in Lansing on March 12 to an estimated 40 people.  In addition, I will provide the Graze Magazine two articles covering the same material.  

2015:

Based on the very preliminary results, the numbers of questions that remain regarding the impact of grazing on soil health and the interpretation of the indicators that were used. Based on the advice of various people to whom we submitted our data, we are planning on continuing this project through the 2015 grazing season. We did not use the dollars earmarked for labor and would use these funds to continue the various testing procedures that were done in 2014. We may vary the timing of our sampling after the harvesting event to try to fine tune the results and pinpoint the effects of each management application.

Objectives/Performance Targets

Accomplishments/Milestones

Impacts and Contributions/Outcomes