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‘Loose Fluffy Dirt’ (05/13/21)

An interesting question was asked by a producer recently, whether there is an official texture/aggregate designation to describe ‘loose fluffy dirt’.

An interesting question was asked by a producer recently, whether there is an official texture/aggregate designation to describe ‘loose fluffy dirt’. Of course, the unofficial designation would be more aptly described as ‘loose fluffy soil’ if the material was actually in a field, rather than the fence line, ditch, tree belt or road. If it was in the latter, ‘loose fluffy dirt’ would be a proper descriptor.

The USDA-NRCS has a designation for this material as an aggregate class named ‘single-grain structure’. Single-grain structure is usually used to describe structure found with coarse sand grain dominated soil, such as found in a Sioux soil series. All of our state soils have a little or a lot of smectitic, shrinking-swelling clays, which expand and contract with wetting-drying and freeze-thaw. The many freeze-thaw events we have had this spring combined with very dry conditions has broken down larger, more stable aggregates into single-grain structures resembling dust. This dust is easily blown away by winds. The larger single-grains may end up in the farmers’ ditch, or in the neighbors no-till field, but the majority ends up almost anywhere on earth, carried by winds to high altitudes and moved hundreds/thousands of miles away. Farmers with years of continuous no-till history are sheltered from this problem, not only due to the residue which slows surface wind velocity, but due to the undisrupted mesh of fungal hyphae, last-years roots, and binding agents from past discharge of the vast array of soil microorganisms that are present in this tillage management system.

Rainfall on single-grain soil will help bind the soil particles together briefly by weak bonding between the polar water molecules and the clay/organic matter negative charges. Heavy rainfall will serve to easily move the soil away through water erosion, and when drying a crust will form. The best-case scenario is light rainfall over days that will provide soil moisture for crop germination and growth and increased soil microbial populations that will discharge materials that start the aggregation process and keep the soil in place.

 

Dave Franzen

Extension Soil Specialist

701-799-2565

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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