The best method to establish the aggregate stability of a soil

November 20, 2012

Look through the Eijkelkamp Product Catalogue and you may miss page 205 which features the Wet Sieving Apparatus Set, to determine the aggregate stability of a soil.

Well, you could argue – who cares? But if you were a farmer, horticulturist or anyone involved in food/plant production the aggregate stability of a soil – the resistance of the soil structure against mechanical or physical-chemical destructive forces – is important information to know because the structure of a soil is one of the main factors controlling plant growth as it influences root penetration, soil temperature and gas diffusion, water transport and seedling emergence – all vital statistics for growers.

In addition, if you work in land conservation (research into soil erosion, land degradation, land conservation, salinization, impact of wind farms on the surrounding land or sustainable agriculture) knowing the sensitivity of a soil to water and wind erosion which might be prevented by mulching the soil surface is vital. It can also help improve tillage programmes which may be adapted to the specific soil type and crop demands.

Soil structure is defined by the combination or arrangement of primary soil particles into compound elements which are separated from adjoining structural elements by surfaces of weakness. Soil texture, soil structure and the type of clay mineral, organic matter content and type, cementing agents and cropping history all influence the soils aggregate stability.

Among some of the mechanical destructive forces is soil tillage, impact of heavy machinery, treading by animals and raindrop splashes. The physical-chemical forces affecting soil are slaking – the process in which soil disintegrates and crumbles when exposed to moisture, swelling and shrinkage, dispersion and flocculation – the process wherein colloids come out of suspension in the form of floc or flakes.

Slaking is the process of structure breakdown under the influence of wetting soil aggregates due to the swelling of clay minerals, dissolving of cementing agents, air explosion or reduction in pore water suction. Slaking can cause the formation of a superficial crust, reducing water infiltration and enhancing sediment loss by downward transportation with surface water run-off.

The old fashioned method of establishing the aggregate stability of soil was to dry the soil samples out in drying ovens – time consuming and expensive. So our very clever Wet Sieving Apparatus can be used to determine a soil’s aggregate stability using the principle that unstable aggregates break down more easily than stable aggregates when immersed in water. So the kit will determine a soils susceptibility for splash erosion, measuring grains from 1 to 2mm.

The kit works when the eight sieves are filled with a measured amount of soil aggregate, each is immersed in water which is vigorously shaken for a fixed amount of time and the unstable aggregates will fall apart and pass through the sieve to be collected in a water-filled can. The testing procedure results in an index for aggregate stability. More information on this equipment can be found here.