April! Bring on the showers!!!
We continue our series on capturing rainwater. From our last episode, we learned that while harvesting rainwater is a great idea, few of us have a cistern large enough to store enough water to carry us through summer droughts. Rain barrels and rainwater collection tanks, although handy, are woefully inadequate in capturing the high volumes that run off our roofs, much less what disappears down driveways. We need an easy fix, but the problems are complex. The forecast for our climate indicates decreasing rainfall for many parts of the world and increasing storm events. What can we do?
Actually – a lot!
During storms, water can come down so hard and fast, it just runs off in the path of least resistance. We need to slow that water down, direct it where we want it to go, and let it sink in. Whether the channel be via trenches, swales, or other means into pits, ponds, rain gardens, or other earthworks – as it turns out – the #1 best place to store the water is *in the soil.* However, all soils are not alike, as anyone knows who has watched water run down a dusty hillside without seeming to get anything wet.
A Side Trip into the Rainforest
As a side story, we recently took a hike in the Quinault Rainforest to a small lake. There had been so much rain, the creeks were overflowing the banks onto the trail. The trail, hardpacked from all the hikers, was the perfect conduit, and the water swiftly ran ankle-deep down the hill. Where the water overflowed into the forest floor, however, it just disappeared into the thick cushion of moss, fallen leaves, and pine needles, sinking into the porous depths and down, down the channels left by roots. The contrast was obvious.
(And That Right There, I thought, is why we don’t want to step into our fluffy garden beds when they are wet.)
Course, that was the rain forest. We are living in the semi-desert area in the rain shadow of the Olympics where we get 15, not 110, inches of rain per year.
Organic Matter Is the Key
But the point is – what you want is a rich soil full of organic matter that can act like a sponge. In fact, according to the USDA, soil organic matter can hold 10-1000 times more water and nutrients than just regular ol’ dirt (aka “mineral soil”). My first reaction to reading that was, “well, that’s a pretty big range.” Everyone’s land is different, though, and building the soil is a process.
How it Works
It’s simple, really. When we add compost and water to soil, we feed the microbial communities, which in turn feed the plants. If the soil is dry and alkaline, more bacteria thrive and plants that prefer a bacterial-dominated environment will proliferate (a lot of our annuals and also weeds). If the soil is more moist and acidic, more fungal communities will grow, and more fungi-loving plants will thrive there (a lot of our trees and shrubs). When we plant more tall perennials, they actually help to conserve water by buffering the wind and moderating temperatures. The roots grow deep, capture and store carbon, and exude nutrients that attract and feed soil microbes. The leaf litter creates a mulch that further conserves moisture, provides more food, and makes the soil more absorbent.
Storing water in the soil doesn’t have to be a complicated construction project. It’s just a way of slowing everything down and of giving the roots, fungi, and creatures in the soil a chance to use it. Instead of running off the surface, the water sinks into place, recharging the aquifer. Slowly, via capillary action, some of it eventually rises back up, quite possibly at a time when surface roots most need it. It transpires through the leaves of shrubs and trees, cooling the air around them. By sinking water into the earth and planting shrubs and trees to act as a pump to bring it back up, we are creating microclimates to our advantage. Some of this water evaporates into clouds and eventually returns back to the earth. It’s a beautiful circulating system, and we just need to learn work with it.
I don’t think I used to fully appreciate the roles of soil and vegetation in this whole process. I am still learning.
How to Increase Available Water Capacity: The Relationship of Compost and Soil
The USDA Natural Resources Conservation Service (NRCS) has several online articles about how the composition of soils, pH, amount of organic matter, and other factors affect “available water capacity,” which is simply a determination of how much water can be stored in the soil and be made available to plants. If you live in an area that supplies as much water as a plant can use from day to day, that’s great. But for those of us whose plants have to ride the roller coaster of too much rain in some seasons to withering drought in others, the capacity of the soil to hold water between rain events can be critical. A soil high in organic matter not only supports small organisms that make nutrients available to the plants, it also acts as a buffer between rain events. Extreme events are predicted to become more common.
Soil Composition and Why it Matters
The kind of soil makes a huge difference. Rocks and sand provide great drainage – which does just that: allows the water to drain away without storing it. Percentages of sand, silt, and clay all factor into the mix. According to an article in the Journal of Soil and Water Conservation, each 1% of organic matter increases water holding capacity by 1.5 to 1.7 times. This can be huge! By adding as little as 3% more organic matter, the soil will make available 4.5% to 5.1% more water – a great insurance policy.
Choices in Organic Matter – What Kind is Best?
A recent study published in Science of the Total Environment compared the advantages of different soil amendments (biochar, compost, and straw) in their abilities to build microbial communities, affect soil structure, increase water holding capacity, and filter or metabolize contaminants, with positive results on all accounts.
The authors concluded that biochar is the least practical, being far more expensive as an amendment and not nearly as available as straw or compost. Interestingly, of the three amendments, straw was determined to be the highest ranking in “quality”and compost the least, based on the idea that compost might have non-decomposed materials and possibly pollutants from households and parks.
I have to respectfully disagree with this conclusion. How can straw possibly have the same nutritive value as compost? Most of the straw mulch I have used still contains a lot of seeds – a great way to plant grass in the garden!
I then realized that this European study must be referring to regional compost facilities, such as those found in city landfills, which often accept waste from unknown sources. They make a point. Bottom line: when it comes to compost, make your own when you can, know what’s in it, and know where it comes from!
Adding organic matter to the soil to build the soil structure to increase nutrient value and water-holding capacity seems obvious to me – but it’s also good to understand how different factors interact. A lot, as mentioned above, depends on the initial soil texture (e.g., clay vs. sand). We also know that soil organisms break down the organic matter into a form the plants can use. We assume that all we have to do is feed these little buggers and they will take care of the rest. However, the soil food “web” is a network of many pathways. Organic matter, water, temperature, oxygen levels, pH, and other factors all interact to affect availability of nutrients (Siedt et al. 2021). Tweak one – everything changes.
To Save the World, Just Add Compost
Clearly, we have a lot to learn and the ag science is ever-evolving. My solution as a backyard gardener is not to measure every last metric, but to recognize that soil organisms are very sensitive to changes in water, nutrient availability, and climate – and a healthy soil community is the key to growing great plants. We need a balance of all the trophic levels of communities, from bacteria and fungi on up to voles and moles tunneling through the soil to eat worms and insects, for it to work.
There I said it: even moles and voles have a role in our backyards. Agggh.
Seriously, though – even a rudimentary appreciation of how a couple of shovels of compost, some water, and a little mulch can affect the pH, available organic matter, and nutrient levels of the soil, which will then support strong communities of soil organisms that make nutrients available to strengthen plant growth, thereby increasing the nutrient density of our food, and consequently, improving our health and the health of our children, and over time, the health of our children’s children – can help us realize how such a simple act of kindness to the soil can even perhaps reverse climate change and basically save humanity!
If you followed that last sentence, just remember this: When in doubt, toss on more mulch. Leave no soil bare. Protect the water.
An Easy Way to Add Organic Matter: Leave the Roots
The reality is, we can never have enough compost and mulch. In rangelands, though, I was surprised to find out what a difference roots can make. They begin by holding the soil together. When the above-ground vegetation dies back, the roots are decomposed by soil organisms. According to the USDA Natural Resources Conservation Service (NRCS), depending on conditions, 25-50% of these roots can be converted into organic matter.
A light bulb went off here for me because our land (although I like to think of it as a food forest), was historically part of an old dairy farm. Over the years, the land was overgrazed; not much was added in; a whole lot was taken out. Thistles and other opportunistic invasives have thrived here.
Technically, this region is classified as “semi-desert.” The arid “Sequim Prairie” was transformed into farms when early pioneers hand dug over 100 miles of irrigation ditches to channel water from the nearby river. “Where water is wealth” was the slogan.
It has a different meaning to me now.
The USDA recognition of the importance of roots to rangeland soils is significant. Why hurt myself pulling weeds? If we think of trying to work with nature, rather than against her, we can use these roots (or rather, the organisms that devour them) to our advantage. I like that idea. Let them do the work.
Another Look at Roots – Planning for the Underground Story
Beyond initial considerations of sun, water, and soil when selecting plants, think about how the roots are structured to get the water and nutrients they need. A shallow-rooted plant might be able to grow in dry conditions or conversely, require frequent watering. A deep-rooted plant can go for long periods without water and has the root structure to seek out what it needs.
By combining tap-rooted plants with those with spreading roots and arranging them so they stack in vertical space (and time) both below and above ground, we can create combinations that can support one another in a relatively small area without competition. This diversity, each occupying their own niche, will slow the water down for you, relieve any pooling issues, and thank you for it.
Similarly, deep-rooted plants that enjoy more water and are more cold-tolerant grow well in the bottoms of basins; more drought-tolerant species can survive well on the upper edges. Deeper rooted trees and shrubs are also good candidates for holding the berms of swales in place and taking advantage of that water source.
And last but not least, there is the matter of compaction: compacted soil causes runoff, not absorption, as observed on the trail through the rainforest. Plus, the act of compacting the soil squishes the air out, and soil organisms, like every other living thing, need air to breathe. If they can’t breathe, they die, and then they can’t provide food to plants.
In looking at our landscapes, we might ask, how easy is it for roots to penetrate the soil – and how deep do they normally grow? The deeper they grow, the deeper carbon is planted into the soil. How deep can the water sink in? And in the opposite direction, how quickly does the available water rise to the surface and evaporate either from the soil surface or from the leaves of plants (evapotranspiration)?
Although saturated soils are important to recharging the aquifer and providing habitat in wetlands, ponds, and other water bodies, it is worth noting that anaerobic soils give off methane. As with compaction, water will replace the air that microorganisms need to breathe, thereby providing an environment for anaerobic bacteria. Wetlands possibly contribute 25% of the world’s methane to the atmosphere. So there’s that.
Plant Allies: Using Plants to Moderate Water Flows, Create Microclimates, and Protect Water and Soil
It seems like an oxymoron to plant plants to conserve water. Yet plants are our ultimate allies (along with soil microbes, of course – they go together). Trees and shrubs create microclimates that lower temperatures, buffer wind, reduce evaporation, and build soil.
The willows, for example, are great at buffering the wind. They also collect fog and that Northwest drizzle that fills the air but doesn’t seem to form actual droplets, and then they “rain” it down on the plants below. This rain, rich in nutrients, has a gentle impact on the soil. (Plus, the willows provide habitat, early pollen for bees, basketry and fencing material, and, of course, they look very cool.)
Insights from an Indiana Farmer
Before I close, I have to share the story of Dan DeSutter, a young Indiana farmer who grows 4400 acres of corn, soybeans, wheat, beef, and cover crops on some silty-clay loam soils. This is phenomenal to me. He is about as far removed from the kind of backyard gardening I do in almost every way imaginable – but I really like this guy, and I think we can all learn from him. He is keenly aware of how we have created a broken system and how destructive modern ag is to our climate – and he and his father have set out to do something about it. Working from the idea that some of our most productive soils were built through prairie ecosystems, he tries to mimic nature whenever and wherever possible. On the native prairies, for example, he observes that
- the soil is always covered; there is no bare ground;
- there is always something growing throughout the year, meaning, there are actively growing roots nearly year round – and millions of soil organisms depend on exudates from living roots, and these organisms are what make nutrients available to plants; and
- there is an abundant diversity of plants and animals, and with this diversity is a balance in predator-prey relationships.
With Midwest sensibility, he notes that he and his father have become livestock farmers, not referring to their herd of beef cattle, but rather to the critters in the soil. “…We now understand that in order to optimize production and maximize the environmental benefits of our cultural practices, we must evaluate all our management decisions within the context of our soil livestock. Understanding how our actions affect our underground workforce has become central to our management decision process.”
With that idea – that soil organisms are an underground workforce or “livestock” – he does everything possible to ensure that they are happy, healthy, and can do their jobs. All animals need oxygen, food, water, and protection from the elements, he reasons. As primary caregiver, he makes sure the soil has the proper calcium-to-magnesium ratios, ensures the soil is porous, and provides an aerobic environment so the soil livestock can breathe. He gives them shelter by mulching the surface to moderate summer temperatures; he increases soil organic matter to better hold in moisture and provide nutrients. By growing something throughout most of the year rather than allowing fields to lie fallow, he creates an active rhizosphere that maximizes microbial activity. The root systems help rebuild the soil organic matter. He and his father apply no-till practices, add cover crops and manures, and encourage earthworm populations.
“When confronted with challenges and obstacles in an agronomic system, look first to nature for the solution. In almost every case, she has already figured out a solution that will be far more potent than the best laboratories can conceive.”~Dan DeSutter. “One Indiana Farmer’s Response to Weather Variations.” Journal of Soil and Water Conservation, November 2014, 69 (6) 200A-202A
The DeSutters have shown by example that better soil health means higher yields and reduced costs, as well as having a positive impact on the environment. Other farmers are sure to take notice. Thank you, Dan DeSutter! Well-said.
Final Takeaways from the USDA with Regard to Soil:
It is encouraging to apply all these concepts to our garden and the back field (which I now recognize as a depleted rangeland on the Sequim Prairie). Some takeaways for me from reading USDA recommendations that coincide with the DeSutter observations:
- Don’t pull the weeds; just cut them off at ground level (what – not even thistles??)
- Plant cover crops that have a mixture of rooting depths; cut off the top growth, but don’t till it in (The USDA is promoting no-till practices! Awesome!)
- Protect the soil from erosion; minimize bare soil (yes! Microorganisms in the soil are important!)
- Grow more perennials among annual crops. Perennial roots will give off exudates that will feed microbial communities through the winter. These populations will increase and will be going strong by spring. Microbes will break down all those dead roots from the weeds and other organic matter and convert them into plant-available forms. Plants will thereby get a jump start early in the season.
Microbes are fed; plants are fed. Give them food, water, and shelter and the soil will just keep getting better and better, as will the food that is grown there.
The more we keep piling on compost, mulch, and other organic matter, the more we improve the soil texture. The more we improve soil texture, the greater its water-holding capacity, which can restore aquifers, lessen the impact of droughts, and protect our water supply.
The more we improve the soil, build microbial populations, and increase plant growth, the greater the soil’s ability to absorb and store carbon and further moderate climate extremes.
The more water in the soil, the more plants will grow, which will add more humidity to the air, and then the more it will rain, which will help more plants to grow… and on and on in a loop. This is our water cycle.
It can also go in the opposite direction.
The most fundamental element to understand: build the soil and the life in it to better protect the water essential to all life. The future of many species, including our own, is intimately interwoven in this intricate network.
We can turn our current trajectory around.
Now. Let’s all get out there and Mulch the World!
~ * ~
People Doing Good Things:
Soil Carbon Coalition https://soilcarboncoalition.org The Soil Carbon Coalition is a nonprofit organization working to advance the practice, and spread awareness of the opportunity of turning atmospheric carbon into water-holding, fertility-enhancing soil, organic matter, and humus.
Resources, References, & Publications:
Efretuei, Arit. 2016. “Anaerobic Soils – What You Need to Know” Permaculture News, November 4, 2016.
DeSutter, Dan. 2014. “One Indiana Farmer’s Response to Weather Variations.” Journal of Soil and Water Conservation, November 2014, 69 (6) 200A-202A; DOI. (Click on the pdf to read the full article – it is well worth it!)
Libohova, Z., C. Seybold, D. Wysocki, S. Wills, P. Schoeneberger, C. Williams, D. Lindbo, D. Stott, and P.R. Owens. 2018. “Reevaluating the effects of soil organic matter and other properties on available water-holding capacity using the National Cooperative Soil Survey Characterization Database.” Journal of Soil and Water Conservation 73(4):411-421.
Richey, A. S., B. F. Thomas, M.-H. Lo, J. T. Reager, J. S. Famiglietti, K. Voss, S. Swenson, and M. Rodell (2015), Quantifying renewable groundwater stress with GRACE, Water Resour. Res., 51, 5217–5238, doi:10.1002/ 2015WR017349. (A NASA-funded study)
Siedt, Martin, Andreas Schäffera, Kilian, E.C. Smith, Moritz Nabel, Martina Roß-Nickolla, Joost T.van Dongen. 2021. “Comparing straw, compost, and biochar regarding their suitability as agricultural soil amendments to affect soil structure, nutrient leaching, microbial communities, and the fate of pesticides.” Science of the Total Environment, Volume 751, 10 January 2021, 141607.
Science Direct . com (Create a free account to read all kinds of articles classified as “open access” for free!)
USDA, Natural Resources Conservation Service. May 2001. “Rangeland Soil Quality – Organic Matter.” Soil Quality Information Sheet. Rangeland Sheet 6.
USDA NRCS (U.S. Department of Agriculture Natural Resources Conservation Service). Soils.