palouse landscape

By Sally Brown, University of Washington

Abstracts of these resources are available in the searchable Information Portal offered to Northwest Biosolids members.

  1. Soil degradation by erosion
    https://nwbiosolids.org/resource/soil-degradation-erosion

     

  2. Wind erosion potential of a winter wheat–summer fallow rotation after land application of biosolids
    https://nwbiosolids.org/resource/chemical-composition-windblown-dust-emitted-agricultural-soils-amended-biosolids

  3. Biosolids and conservation tillage: Impacts on soil fungal communities in dryland wheat-fallow cropping systems
    https://nwbiosolids.org/resource/biosolids-and-conservation-tillage-impacts-soil-fungal-communities-dryland-wheat-fallow

  4. Dust-associated microbiomes from dryland wheat fields differ with tillage practice and biosolids application
    https://nwbiosolids.org/resource/dust-associated-microbiomes-dryland-wheat-fields-differ-tillage-practice-and-biosolids

  5. Chemical composition of windblown dust emitted from agricultural soils amended with biosolids
    https://nwbiosolids.org/resource/chemical-composition-windblown-dust-emitted-agricultural-soils-amended-biosolids

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.  There 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 - 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.  

WSU wind erosion study
Washington State University set-up a wind tunnel to simulate wind erosion and collect soil erosion measurements comparing biosolids vs. synthetic fertilizer applications and conventional tilling vs. no-till. 

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.