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Compost on rangelands

Author: Shulamit Shroder

Carbon: it’s what diamonds, trees, and humans all have in common. This versatile element is essential for life as we know it, but these days it is wreaking havoc in the atmosphere.

However, when farmers and ranchers apply organic amendments like compost to their fields, they can reap the benefits of increased soil organic matter while also keeping carbon out of the atmosphere. Plus, California Department of Food and Agriculture’s Healthy Soils initiative provides funding for farmers and ranchers to apply compost to their fields, so you wouldn’t have to invest a huge chunk of your own money in this endeavor.

But first, what’s the evidence for the benefits of compost applications on rangeland? And don’t grazing animals already do this for free?

The Silver Lab up at UC Berkeley, led by Dr. Whendee Silver, has been studying those questions for the past decade as part of the Marin Carbon Project. They applied compost at two different range locations, one on the coast and the other in the Sierra foothills, and then measured the results. They found that, in both locations, a onetime application of compost resulted in increased carbon storage in the rangelands soils and in increased plant productivity for all 3 years of the study (Ryals & Silver, 2013). Plus, the onetime application of compost did not significantly affect the plant community structure (Ryals et al, 2016). The Lab also modeled greenhouse gas fluxes and found that applying compost resulted in a net benefit to greenhouse gas emissions that lasted for decades (Ryals et al, 2015). The Marin Carbon Project has demonstrated that applying compost to rangelands can put huge amounts of carbon into the soil – and keep it there.

What about applying raw manure? A study on Marin County dairies looked at applying large amounts of un-composted manure to rangeland. It found that while manure application would increase soil carbon storage, it would also increase N2O emissions. This would then offset the benefits from the carbon sequestration. In addition, the plant community changed from predominantly perennial grasses to mostly annual grasses. Applying composted manure instead could reduce the N2O emissions (Owens et al, 2015). When grazing animals add raw manure to the field, even though they can increase soil carbon storage, they may also increase N2O emissions and contribute to a change in the field’s plant community.

Keep in mind, though, that these trials were in Marin County, which receives a lot more rain than we do in the southern San Joaquin Valley. Jeff Borum, a soil health conservationist with the East Stanislaus Resource Conservation District, has spent the past 2 and a half years experimenting with compost applications on rangelands at 16 locations throughout California, including in Tulare County.

These sites all have different climates, so this project should better represent the various ecosystems in California than the Marin Carbon Project did. The researchers on this project are still measuring how compost applications might affect factors like water infiltration rates, compaction, forage production, nematode populations, soil carbon, and pH.  

However, preliminary data is promising. The drier sites, like the Kaweah Oaks preserve in Tulare County, have shown greater increases in soil carbon than the wetter areas. 14 of the 16 sites exhibited increases in soil carbon – only Mendocino and San Mateo did not record changes. The researchers anticipate this increase will result in higher forage production for those 14 sites (J. Borum, personal communication, May 20, 2019). Borum’s team has found that applying a quarter inch layer of compost hits the sweet spot for maximizing carbon sequestration.

Researchers in other places have also found benefits to applying organic materials, like biosolids, to grasslands.

Scientists in the Chihuahua desert found that adding biosolids increased water infiltration and decreased erosion rates of grassland and shrubland ecosystems (Wester et al, 2011). Grazing animals tended to spend more time in the amended areas. On average, the amendments did not affect the animals’ weight. However, in years with average, non-droughty precipitation, the animals gained more weight when grazing on amended areas (Wester et al, 2011). Organic matter can also increase the soil’s water holding capacity. This enables the soil to better resist drought and to continue to support the grasses and shrubs upon which cows, sheep, and goats depend (Westbrook & Marshall, 2014). These researchers have thus found positive effects on both soil and animal health from adding composted organic matter to rangelands.

In conclusion, increasing your soil’s organic matter content can sequester carbon, increase water infiltration, decrease erosion rates, increase water-holding capacity, and improve plant productivity. Applying compost is one way to improve your soil organic matter.

The Healthy Soils initiative will help pay for compost applications for 3 years. With the incentives program, you have to add 6-8 tons of compost per acre per year for 3 years. If you want to test different amounts of compost and measure its effects on soil health, you can apply for a demonstration project grant.  

For more information about the Healthy Soils program and how you can apply for the next grant cycle, reach out to Shulamit Shroder, in Kern County, at 661-868-6218 or sashroder@ucanr.edu.  


Literature cited:

  1. Owen, J. J., Parton, W. J., & Silver, W. L. (2015). Long-term impacts of manure amendments on carbon and greenhouse gas dynamics of rangelands. Global change biology, 21(12), 4533-4547.
  2. Ryals, R., & Silver, W. L. (2013). Effects of organic matter amendments on net primary productivity and greenhouse gas emissions in annual grasslands. Ecological Applications, 23(1), 46-59.
  3. Ryals, R., Eviner, V. T., Stein, C., Suding, K. N., & Silver, W. L. (2016). Grassland compost amendments increase plant production without changing plant communities. Ecosphere, 7(3), e01270.
  4. Ryals, R., Hartman, M. D., Parton, W. J., DeLonge, M. S., & Silver, W. L. (2015). Long-term climate change mitigation potential with organic matter management on grasslands. Ecological Applications, 25(2), 531-545.
  5. Westbrook, J., & Marshall, S. E. (2014). Stewarding Soil: promoting soil quality to meet management objectives on California rangelands.
  6. Wester, D. B., Sosebee, R. E., Zartman, R. E., Fish, E. B., Villalobos, J. C., Mata-Gonzalez, R., ... & Moffet, C. A. (2011). Biosolids effects in Chihuahuan desert rangelands: a ten-year study. Applied and Environmental Soil Science, 2011.