By Sally Brown, University of Washington
Abstracts of these resources are available in the searchable Information Portal offered to Northwest Biosolids members.
Soil health and sustainability: managing the biotic component of soil quality
Composted biosolids enhance fertility of a sandy loam soil under dairy pasture
Long-term effects of biosolids on soil quality and fertility
Long-term crop and soil response to biosolids applications in dryland wheat
Soil Enrichment Protocol: Reducing emissions and enhancing soil carbon sequestration on agricultural lands
Clearly, we’ve all been more than a little obsessed with our own health and well- being lately. The library this month is also about health and well- being – but with a focus on soils. This is prompted by the Climate Action Reserve that is working on developing a protocol to give credit to people who help heal soils. There is a good chance that organic amendments are high up there in the tool box for this. When/ if they rate credits is a real question. Let’s start with sick soils. Who would have thought that soils get sick? Actually, there is a long history of soil degradation and the resulting impacts on the people who depend on them. For that I’d recommend you get a copy of Dirt- the Erosion of Civilizations by David Montgomery. Speaking personally, I’ve had enough death and destruction for the time being. So I am not going to read that book by Montgomery. We know how to fix soils- or at least we have a pretty good general idea. Instead of focusing on the destruction, let’s focus on the restoration.
The first paper in the library is a very nice review of the whole concept of soil health and why it is important. Over 40% of the world’s agricultural soils are hurting. This is from a combination of factors including soil erosion, extensive cultivation, over- grazing, land clearing , salinization (too high in soluble salts) and desertification (turning soils into the Gobi desert equivalent). There is also a discussion of the impacts of poor soil health apart from not having enough to eat. Excess nutrient runoff from soils and the creation of dead zones (areas of depleted oxygen) in fresh and salt waters are also a consequence of degraded soils. The authors go over basic definitions of soil health- optimal functioning is the short answer. They then spend a lot of time talking about the best ways to measure it. We used to understand /study soils from three different perspectives. We considered physical properties, biological properties and chemical properties. The Soil Science Society of America even has three volumes on how you analyze each of these. When you consider soils from a soil health perspective, it turns out that they are all related. This makes the analysis a bit more complicated. It can be very complicated, but it is also critical to develop simplified tools as not every person who works the soil is likely to install replicated field plots and have a large analysis budget with graduate students. Ideally indices are relatively simple and straightforward to measure. They also reflect the interrelationship of the physical, biological and chemical. That translates to low bulk density, good aggregation, and active soil food web and sufficient available nutrients. Take home quote here: ‘Note that soil organic matter serves as a primary indicator of soil quality and health for both scientists and farmers’. The table below shows a summary of the paper.
If you look at this summary biosolids have the potential to fit in in several sections. We can be the medicine here. In fact, two long-term biosolids sites are currently being monitored by the USDA as part of their soil health study. One of those is WSU’s own dryland wheat study, the other is in CO. Many of the studies on land application of biosolids have focused on the safety with a lens on the particular contaminant du jour. There are a few that consider the broader issue of biosolids and soil health without that requisite emphasis. The second paper in the library comes out of New Zealand. This is a relatively early paper (2004) and so there is a requisite discussion of metals, but the focus is primarily on benefits. The authors applied composted biosolids to a pasture. In addition to measures in the pasture, the authors also collected the soils and used them in pot trials. They saw increased yield from the pot trials and improvements in soils from the field trials. Higher carbon, nutrients, cation exchange capacity all increased. From the microbial end, they also saw increased populations (a good thing), that that population was carrying out their business (respiration and anaerobically mineralisable N). This early paper used a range of indices and showed that adding biosolids compost to a field improved the health of the soil in that field.
From there we go to a more recent study from England. Here they use the terms soil quality and fertility, but again are using a broad range of soil variables to evaluate the impact of biosolids on soil health. This study has been in the library before but not with the lens of soil health as the monthly focus. Four sites, biosolids applications over time at agronomic loading rates. Measures included total and light organic matter, water holding infiltration and aggregate stability, available and total nutrients, and earthworm numbers. In other words, physical, chemical and biological indicators were all included. In all cases the biosolids did the trick- improvements were seen with response varying by soil type.
Last evidence of the importance of biosolids in soil health comes right from home. The dryland wheat plots established by WSU in the 1990s, and now part of the USDA Soil Health study were evaluated in this paper published in 2013. The authors measured changes in yield, protein content of wheat, and soil carbon, nitrogen and phosphorus. On the physical end of things bulk density was measured. Total microbial biomass and general types of bacteria and fungi were also measured. Biosolids at the medium and high rates were the best- high yields, higher protein in the grain, lower bulk density, more carbon storage, higher nutrients and more critters. The paper showed that the biosolids increased the ratio of bacteria to fungi in the soil. This happened because of increases in the populations of aerobic, gram positive and negative and anaerobic bacteria increased. Fungal populations stayed the same across all treatments. Our knowledge of soil microbes isn’t sophisticated enough to really comment on this. We can say that in general, higher populations mean healthier as they reflect the fact that there is more to eat.
So three papers from three continents, all showing that biosolids improve soil health from the physical, chemical, and biological metrics used. Will they count in the CAR protocol on soil enrichment? The last article in the library is the draft protocol. You want some dry reading- this fits the bill. Developing a protocol to give carbon credits has to be a conservative exercise. You are basically creating value out of too thick air- so to speak. In my opinion, this first draft is over the top, despite that constraint. I’ve submitted comments including using newer values for default N2O emissions (see February 2020 library) and using per ton amendment applied values for different amendments, again based on peer review research. We will see what happens with this. I know that CASA has also submitted comments. There is strong research to support giving credits for amendment use to improve soil health. It would be great if the CAR protocol recognizes this. In the meantime, stay healthy. Next month we go to contaminants.