Partnering with Natural Resources Conservation ServiceResource Conservation District California Carbon ProjectUniversity of California Cooperative ExtensionPoint Blue Conservation Science, Berkeley Lab and Silver Lab, we recently went out in the pasture for a new Conservation Field Trial to apply one-quarter of an inch of compost to the lands at TomKat Ranch.

Recent evidence from California Carbon Project and Whendee Silver has shown that a small amount of compost applied to rangeland can increase soil carbon sequestration for 30 years or more. Increasing carbon sequestration and soil organic matter not only helps mitigate climate change but also improves the fertility and water-holding capacity of the soil for better and more plentiful forage and a healthier ecosystem overall.

The compost jumpstarts the biology and sustains it by providing physical carbon to feed the microbes, which is a little different from a compost tea that also jumsptarts soil biology. When combined with managed grazing it could be just the ticket for this particular pasture that has been underperforming for quite some time. Many years ago, this pasture was farmed for flaxseed and hay, and all of the native grasses were tilled under. What’s left are a bunch of annual grasses and a homogenous plow layer as pointed out by UC soil crewmember, Yang Lin, when the bulk density soil pits were dug. Yang pointed to the cross section of soil to highlight how the soil strata were indicative of historical plowing and, sure enough, you can see it right here in the photo.

Soil strata indicative of historical plowing.

Soil strata indicative of historical plowing.

The aggregates in the soil were really interesting, particularly when we broke off a chunk from near the plant roots. As you can see, there is rich organic matter adsorbed to the aggregate. That beautiful black stuff is the result of root exudates that plants send out through their roots to incentivize microbes to build soil fertility and structure. Like an underground marketplace, the plants send the exudates (mostly sugars and organic acids) to feed microbes that reciprocate by providing food and water for the plants. Bacteria, fungi, and invertebrates are the primary players in this exchange.

Rich organic matter adsorbed to the soil aggregates.

Rich organic matter adsorbed to the soil aggregates.

Looking at the side of the soil pit, you can see plant roots and soil organic matter that have formed from root exudates  – all powered by photosynthesis! In this process, the plants take in sunlight and carbon dioxide and make glucose and sucrose out of that sunshine. Then, they take those sugars and polymerize them, or put another way, rearrange the sugars to form leaves, shoots, and roots. And for the grand finale, the plants send exudates through the roots to provide an incentive for the microbes to get a good meal out of the deal. This process is what grows soil. That’s right, soil grows!

Plant roots and soil organic matter formed from root exudates.

Plant roots and soil organic matter formed from root exudates.

The soil pits were dug for bulk density measurements. Bulk density measures a specific amount of dry soil divided by its volume to help determine compaction that can limit root growth and water holding capacity. This is a little different approach than we have taken before and it was fascinating to observe the technique used by UC soil crewmember Sam Grubinger. First, you dig a roughly 3×3’ pit. We had a backhoe, thank goodness. From there, like any bulk density measurement, you clear off the top duff and place the bulk density ring on the soil at the edge of the pit. Then Sam hammered on the cylinder until it got to 10cm depth and excavated the soil around the cylinder to make a clear path for the paint scraper-like tool to cut the soil from the bottom of the ring to ensure a predictable volume for measurement.

Hammering 10cm cylinder.

Hammering the bulk density cylinder.

While Sam was hammering away in the soil pit, the other members of the soil crew, Allegra Mayer and Gisele Herren, were laying out the transects for the soil core sampling. They carefully selected the transects giving consideration to the slope and nature of the land so that results would not be skewed one way or another. The plot is on a hilltop so it’s not completely flat. Keeping the contours in mind while anticipating water flow is critical to ensuring meaningful results.

Marking and laying the transects for the sample plot.

Marking and laying the transects for the sample plot.

The team used soil augers to dig down to 0-10cm, 10-30cm, 30-50cm, and 50-100cm levels to collect the soil cores for analysis. It’s a lot of work! Those cores don’t dig themselves out, that’s for sure. This time of year (October) in California, the soil is very dry and some spots are like concrete since it had been 6 months from the last rain. Conveniently, we got about 2.5” of rain a few days later.

Using soil augers to collect soil cores.

Using soil augers to collect soil cores.

The soil cores will be taken to Silver Lab where they will be processed for bulk density, elemental analysis, and Berkeley Lab for biological testing. Next step is the compost application. We will be sure to document the process to share in a couple of weeks!

Below is the tentative protocol for this project. It will be updated as needed.

Conservation Field Trial (GM 403.3)
Range Compost Application
USDA – NRCS Davis, CA

Background

Many acres of rangeland in California had been farmed to small grain crops during the 1920s until the end of WWII. During this time, equipment was used to till the soil on an annual basis. As the market decreased for small grains, so did dryland farming on these lands.  They were left fallow to return to rangelands. Today many of those areas exhibit poor resource conditions with low soil aggregate stability, low organic matter, soil surface loss and are infested with various annual weedy species including but not limited to medusahead, barbed goatgrass and yellow star thistle. This Conservation Field Trial will target these degraded rangelands for compost application with hopes that added organic matter and nutrients will improve soil and rangeland health.

Objective

The objective of the study is to track changes in the following after compost application:

  1. Species composition
  2. Forage production
  3. Soil aggregate stability
  4. Organic Matter
  5. Infiltration rates
  6. Organic Carbon

The project will be done on grazed rangelands. Previous studies have shown that forage production improvements of up to 60% have occurred after compost application. Compost has been shown to increase nutrient cycling, improve soil fertility and increase soil microbes, thus increase soil carbon sequestration. This has not been well documented at the field level.

Tentative Protocol for NRCS Range Compost Field Trials (CFT)

At each site, a one-acre plot will be staked and marked with GPS coordinates.  Conditions will be measured and documented well inside the boundaries in order to account for edge effect.

  1. Soil carbon at 0-10cm, 10-30cm, 30-50cm, 50-100cm
    1. Site will be sampled on both compost and control locations (2 plots) prior to compost applications and again at the end of the growing season (April-June).
      1. For each plot, a 50 m transect will be sampled with samples collected at five 10-m increments
      2. Cores samples taken at 0-10cm, 10-30cm, 30-50cm, 50-100cm.
      3. Bulk density sampled near center point of transect @ 10cm increments to 1m. Point will be chosen through random number generation.
      4. At the end of the growing season, the enclosure could be sampled at 0-10 cm and 10-30cm increments in three randomly located replicates per side and depth
    2. Isotope fractionation, 13C and 14C of C fractions
    3. Elemental analysis
  2. Species composition, using line-point intercept, and categorized by species and into functional and structural groups.
    1. 150 ft.(45.72m) transect; data collection locations every 3 ft. (0.91m) with up to three species data points, plus a soil surface data point, at each location
  3. Soil aggregation and aggregate stability
    1. Slake test: ranked from 0 to 6; http://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs142p2_051287.pdf
    2. Other aggregate stability test
  4. Soil types identified and mapped
    1. NRCS Web Soil Survey
  5. Peak vegetation production
    1. Biomass sampling of forage every 30 ft. (9.14m) with a 0.96 ft2 (0.09 m2) hoop on same 150 ft. (45.72m) transect used for species composition
  6. Infiltration rate
    1. Double-ring infiltrometer; http://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs142p2_052494.pdf
  7. Compaction
    1. Penetrometer and observational data
  8. Identify wildlife habitat on site
    1. Visual and auditory observations
  9. Bulk density
    1. See 1., a., iii.
  10. Soil texture
    1. Particle size analysis
  11. pH
    1. pH meter, electrode & probe
  12. Potential N mineralization and nitrification
  13. Microbial biomass C and N
  14. Moisture content at time of sampling
  15. Samples to be air dried and archived

The following is the plot design:

Each trial site is one acre, divided into two equal sized subplots, with one side compost and one side without compost applied. Both subplots are grazed (there is no non-grazed treatment), except at the CA Plant Materials Center in Lockeford. Each plot includes a fenced subplot (50 ft. by 100 ft., 15.24m x 30.28m).  Within the fenced subplot (compost applied and compost not applied) vegetation will be clipped annually at the end of growing season to characterize gross productivity and species composition.  Each subplot is characterized by a 150 ft. transect, with subsampling along transects for soil and vegetative parameters.  In certain instances, trial plot measurements may be altered due to items such as logistical feasibility.

At each site three monitoring transects will occur:

  1. On the ½ acre compost treated side
  2. On the ½ acre control
  3. Within the excluded subplot

Site characterization baseline information will be collected spring, summer, and fall of 2016. Each plot will be geo-referenced at each corner.

Data collection methods will follow those described in the Monitoring Manual for Grassland Shrubland and Savanna Ecosystems, Vol 2. Herrick, J., Van Zee, J., Havstad, K., Burkett, L, Witford, W. USDA – ARS Jornada Experimental Range, 2005.

  1. Line Point Intercept for species composition and percent bare ground
  2. Soil Surface Stability using the soil stability test kit
  3. Forage Production by clipping with a .96 ft2 (0.09 m2) hoop within the exclosure at peak production; after each collection, this area will be mowed down so that the peak production collection for the next year is not altered significantly by residual dry matter (RDM)
  4. Compaction using a penetrometer & infiltration using a double-ring infiltrometer and observational evidence
  5. Soil Carbon/Organic Matter utilizing isotope fractionation and elemental analysis

Parameters to be measured are kept to a minimum to allow for consistent data collection by a diversity of partners on twelve field sites, as well as to keep project cost down to a level consistent with the conservation field trial methodology.  Additional data may be collected by partners at their sites, at their own discretion, and may be included in the final report as appropriate.

Data will be collected, at minimum, once per year at the end of the growing season, which may vary slightly by location.  This will include first year (2016) for baseline data, one year after plot establishment – 2017, Year Two (2018), and Year Three (2019), with a report due at the beginning of Fiscal Year 2020 (October, 2019).

The final report will include site characterization, baseline data results, and treatment response data results, with explanations of any variations from the basic project design.  Also, reference tools such as COMET Planner and the Interim Practice Standard will be used to inform the final report as appropriate and available.  The final report will inform revisions as needed to the interim standard, and specifications and practice implementation requirements for compost applied to rangeland.

Resources needed to accomplish the objective include the sites donated by landowners as described in the Table 1 below. California Carbon Project offered to provide the compost to Cal-Recycle specifications and with quality analyses, to all participating sites.

Partners that have volunteered to assist with data collection, financial support and technical review include:

  1. Point Blue Conservation Science
  2. California Carbon Project
  3. Rathmann Family Foundation
  4. UC Cooperative Extension
  5. East Stanislaus Resource Conservation District
  6. California State Water Quality Control Board
  7. Environmental Protection Agency
  8. Landowners – Various as shown in Table 1

Landowners agree to donate the plots for compost application and document grazing use on the sites (season of use, animal numbers, type and class of livestock, duration of grazing on the site). A Grazing Record Worksheet will be provided to the landowners. Photographs will be taken before grazing and after grazing periods.

As a condition for landowner participation, each trial site must have a contact person and an individual or entity able to secure access to the property so that initial plot lay-out can be completed and baseline conditions assessed. Thereafter, entry must be provided to apply the compost treatment (with assistance from California Carbon Project), and then take periodic measurements as described above.

Technical Responsibility Assignment

The NRCS California State Range Conservationist will be the project coordinator, under the oversight of the State Resource Conservationist and State Conservationist.  The NRCS is providing some start-up funding to support the project with partners willing to provide funds and in-kind services necessary to complete the project. The East Stanislaus RCD will employ a project manager for day to day management. NRCS technical specialist will complete the final report with review from technical partners including UC Cooperative Extension and Range Scientists with California Carbon Project.

Work Plan Signatures Required

The work plan will be signed by the State Conservationist. Additional signatures will be added if necessary by Regional and National review and concurrence.