To view the article abstracts from this months research update follow this link: FEBRUARY 2019 RESEARCH UPDATE
Blowing in the Wind
While a potent way to understand the potential for answers- just ask Bob Dylan- blowing in the wind tends not to be a good thing for soils. While not a good thing, it is a naturally occurring thing. Loess is the official name for windblown soil particles. In fact, many highly fertile soils are formed from loess. The Palouse hills and associated soils in SE Washington State for example were formed from loess. Not only are they nice on the eyes, they are good for the plants.
Losing soil to wind erosion is bad from the place where the soil started out, not for the place where the soil ends up (unless that place is covered by water). The soil particles most prone to erode are the silt fraction. Sand is too heavy and clay is too sticky to be easily moved by wind. Silty soils in relatively dry climates with potential for wind are most likely to erode.
The farmers in Douglas county that have been using biosolids for years know all about wind erosion. Erosion has taken away good topsoil for many years (maybe even blowing it to the Palouse). To hear them talk about it, biosolids have done wonders in helping the soil stay put. You can listen to them talk and even see some soil blow in this clip: https://www.loopforyoursoil.com/what-is-loop/videos-media/. Look at Fertilizing with biosolids: building soil, better crops.
To find out if what the farmers were seeing could be quantified, King County and NW Biosolids partnered with WSU to carry out a replicated field trial testing the impact of tillage practices and biosolids on the wind erosion of soils. In typical WSU fashion, the study was very thorough, testing both how much blew and the characteristics of the remaining soil and the loess. Those studies are the topic for this library.
The first paper is a general review on the issues associated with soil erosion by Rattan Lal. He goes through factors involved in both wind and water erosion and the relationship between soil degradation and erosion. There is a lot of basic good information here. To summarize some of the key points. Soils are more likely to blow away if they are poorly aggregated and dry. Well aggregated soils will have better structure and the individual particles will stick together better. This makes them heavier and less likely to be Gone with the Wind. Take that Scarlett O’Hara. Wet soils are also stickier and heavier. Lal talks about the various iterations of the USLE- the universal soil loss equation and the different iterations of that equation and their associated initials. The key here is the basics of soil erosion in the first part of the article.
From there we move onto the WSU studies. The first details the result of the wind erosion trials. In order to measure wind erosion, you have to set up a wind tunnel. You then blow wind through it at a set speed for a set duration. If you want to really mimic a wind storm you add sand particles. Sand is heavier and more abrasive than silt and clay and blasting sand through the tunnel can result in more erosion. Sand paper is one way to imagine this. Another involves walking on a Pacific Northwest beach in the winter where you can experience it first- hand. The final part of this is collecting the soil that has dislodged and blown to the end of the tunnel. The WSU study was set up in a dry part of the state where dryland wheat is grown in a fallow rotation. Biosolids had been applied for two applications before the study started at 6.5 tons per hectare. Synthetic fertilizer was added as a comparison treatment. The scientists also compared conventional tillage and a version of no till.
The big difference was between no till and conventional tillage, with much more erosion in the conventional tillage. For the second year of wind events, the biosolids amended plots lost less soil than the plots treated with synthetic fertilizer. For example, the mean soil loss with the biosolids in September 2016 was 1771 grams per meter and was 2133 grams per meter in the fertilizer. Now, while everybody can agree that 1771 is less than 2133, statistically the numbers were similar. The only statistical difference was during the June 2016 wind event when the scientists added in the sand. Here the biosolids lost 273 g m-2 and the fertilizer lost 395 g m-2. So, there seemed to be a trend for the biosolids to reduce the blow, but that was only statistically significant for one of the events. The biosolids soils had more carbon and so also held more water than the fertilizer amended soils. What this suggests is that the farmers in Douglas County are not crazy. Over time and multiple biosolids applications, it is likely that the soil blows less, especially since many of those guys have converted to no-till.
The rest of the papers in the library go into detail about the characteristics of the soils in the study -- the ones that stayed put as well as the part that blew away. The 3rd and 4th studies talk about the microbial community in the soils and the dust. The final paper focuses on the chemical characteristics of both the dust and the soil. For the fungal community (#3), it turns out that biosolids addition and/ or no till management don’t result in clear and easy to follow changes in diversity or abundance. For all soils and treatments, one type of fungal community predominated: Ascomycota. There were other phyla, but in much smaller numbers. With the biosolids, the proportion of other types changed enough to be statistically significant and to make the colors on Figure 1 of the paper more interesting, but it is not clear what the significance of this change. Much of the change in the fungal diversity was related to increased carbon in the biosolids treatments. Study #4 considers bacteria as well as fungi. They also consider the populations on the dust particles as well as those in the soil. Think of the Whos both down in Whoville and those deciding to pick up and explore the world. The big difference seen in this study was that the bacteria on the dust from the no-till plots were those associated with eating above ground plant material while those from the conventional till plots were associated with eating below ground plant material. The bacteria on the dust from the biosolids particles were ones that like a diet enriched in carbon because of more carbon in the biosolids amended soils. Clostridium, a family of bacteria that are found in soils but are also found in the human gut. were higher in the biosolids dust than in the fertilizer dust, but were in the minority for both compared to other types of bacteria. The take home here is that soil microbiology is an exciting and very confusing field not for the weak of heart or brain. Of more practical significance, dust from biosolids-amended plots contains a different general population of microbes than those from the fertilizer amended plots. While you can find an imprint of humans on that, it is not anything to cause concern or fear of dust. The major difference is that the microbes from the no-till and biosolids treatments are from families accustomed to richer and better diets than those from the conventional till and fertilizer soils.
The final paper in the series gives the evidence of the richer diets. This paper compares chemical characteristics of the soils and dust from the different treatment. This includes metal (the good ones and the bad ones) and nutrient concentrations. A ton of data is presented here, and it is very easy to get lost in the sheer volume of information. In terms of the volume of metals and nutrients lost per treatment and per event, no clear impacts of biosolids treatment were seen. Heavy metal loss and nutrient loss were similar for the fertilizer and biosolids. However, the soils that had biosolids applied and stayed put had generally higher N, P, C, and S than the corresponding soils with fertilizer added.
To sum up, erosion is a big problem. This series of studies shows that reduced tillage reduces wind erosion. It suggests that adding biosolids can also help, likely more over time and with more biosolids. Biosolids do this likely because they increase soil carbon and soil water holding capacity. When the dust does blow, the dust coming from the biosolids-amended soils is about the same both in terms of disease risk and nutrient movement as the soils coming off fertilizer-amended plots.
Would Bob Dylan approve of this? That answer is likely found in the wind.
Sally Brown, University of Washington