Protecting the watershed Part 2: strive for 5% organic matter
Five percent is the recommended target for soil organic matter (SOM). At these levels, natural soil functions are restored. Because of soil’s ability to manage water, so healthy soil must be the foundation for any watershed protection program. Otherwise, mitigation becomes more complicated and capital-intensive than it has to be — and may never be as effective.
Watershed protection starts with good soil
To rebuild soils:
- For new construction and turf renovation — manufacture rich topsoil at the job site. Add up to 30-50 percent compost to the top 6-8 inches of soil and incorporate. If the existing surface layer of the soil must be removed, stockpile it. Then, bucket blend with 30-50 percent compost and reuse during the landscaping phase. Why? Unless trucked-in topsoil is coming from a never-touched-by-humans site, the soil can be depleted. It may not even be true topsoil. What passes as topsoil in many areas these days is actually the native subsoil, because the topsoil layer has been eroded or scraped away. Subsoil is inert and won’t sustain plant or animal life. Make your own, instead — saves money, too.
- For revitalizing and maintaining established fields and landscapes — feed the soil. Core aerate, top dress with 1-2 inches of compost and rake or back-drag. Repeat using 1/8-to 1/4-inch applications of compost annually. For active playing surfaces, use a product formulated for sports fields (like McGill SportsTurf). Apply the initial 1-2 inches in multiple applications over the course of a year.
- For planting beds — add 30 percent compost to the planting mix.
- Add an organic matter test to annual soil sampling, and keep SOM within desirable ranges for the specific plants. Too much SOM can cause problems. Think like Goldilocks — not too much, not too little, but just right.
Adjust SOM before trying other run-off measures
Expect to see a 30-50 percent reduction in runoff when SOM is in the target range. Then, if additional action is required:
- Add rain barrels and other diversion/collection measures to all downspouts and sheet drainage pathways.
- Plant trees, shrubs and other vegetation where runoff enters stormwater systems and drainage ditches. Check with the highway department, utilities, homeowner associations, etc. if planting in a right-of-way or other easement.
- In riparian zones, the U.S. Geological Survey recommends vegetated strips. Plant swaths 20-100 feet wide on either side of streams and rivers, depending on land use and topography.
- Break up impervious surfaces with vegetated strips and permeable materials or do away with them entirely. Be sure to add compost to the soil mix beneath the vegetation and permeable materials.
- Reduce or eliminate the use of chemical fertilizers. If professional turf managers can establish and maintain grass using only compost, everyone can. Compost reduces the pollutant load in what does run to waterways through filtration/degradation action and volume reduction.
- Mandate the use of compost blankets, socks and berms on all projects where large areas of soil disturbance are anticipated. Compost Best Management Practices (BMPs) can be vegetated and designed to remain onsite as a permanent landscape feature.
U.S. Composting Council’s Strive for 5% campaign webpage