Healthy Soils Compost Spread Update
In 2017 we applied for and secured a cost share grant through CDFA for a broad acre compost application on rangelands. The grant was built off of the science done in the Marin Carbon Projectwhich demonstrated that a ½” application of compost on annual range land in combination with cattle grazing has the potential to sequester carbon in the initial year and for many years after the application is complete.
In using what we believe is a best practice monitoring protocol, we also had multiple exclosures totaling about 20 acres and 5 monitoring points in the exclosures. The compost treatment protocol designed by the CDFA split the application up into 3 years. Instead of applying 3/8 of an inch one time we are essentially applying 1/8 of an inch three times. The first application was in 2018 and we have resampled the baseline soil monitoring locations since then.
The results after the first year are encouraging even though sampling on an annual basis is not recommended.Across the 6 soil monitoring sites where we applied compost, we saw an average overall change in carbon from 1.43% (2018) to 1.52% (2019). That is a 5.94% relative increase in % C which is considered meaningful management change in the soil circles. The 5 exclosures where compost was not applied averaged 1.59% in (2018) and decreased in carbon to 1.57% (2019), which is a 1.3% relative decrease.
In the first year on the first day of 2018 (of two days of application) without getting into too many details we had a lower application rate in terms of dry tons of the compost then we had planned on. We ended up applying 4 to 4.6 tons to the acre. However, on the second day of application we were able to secure some more compost and actually applied at 5 tons to the acre. This is significant because when we re-monitored in 2019 the sites that got four tons to the acre showed a 4.4 relative increase in carbon. Where the sites that got five tons to the acre showed a 13.1% increase in carbon.
When we went back to apply in 2019 we made sure to apply at least at 5 dry tons to the acre so it will be interesting to see what the changes look like when we re-monitor in 2020. Additionally, we are an educational site for the healthy soils initiative and had had multiple field days we’re over 90 people from the community have come to learn how to carry out the technical components of the program from our experience. Overall, the program feels like a success from the start and with data just coming in we feel like we have years of learning yet to come.
