Hardsetting soils: a review

Abstract

Hardsetting soils have been defined as soils that set to a hard, structureless mass during drying and are thereafter difficult or impossible to cultivate until the profile is rewetted. Soil strength increases rapidly as the soil dries, and so seedlings must grow quickly before soil strength becomes too high for root growth or shoot emergence. Recent work on the mechanisms of hardsetting confirms that aggregate disruption through slaking and dispersion on wetting leads to coalescence. Bridging by dispersed particles under matric potential makes a soil hardset. Failure to recover from a coalesced state as the soil dries leaves it with a massive structure. This paper reviews the worldwide occurrence of hardsetting soils, the evolution of definitions of hardsetting, and the use of those definitions in soil classification with particular emphasis on Australia. Measurement of hardsetting includes methods such as visual score of slaking and dispersion, penetration resistance, fall-cone penetration, dispersion, fractions of soil organic matter, friability index, modulus of rupture, and a particular use of the soil water retention curve. Overcoming problems associated with hardsetting soils and their ongoing management is difficult. Further work is needed on the reasons for variable responses to tillage, no tillage, and pasture. Modifying soil texture has limited application, and increasing soil organic matter under cropping is difficult in low-rainfall areas. Polymers have been shown to be beneficial. Mulching maintains higher soil moisture and therefore a softer surface, while biochar shows inconsistent effects. Controlled traffic is a key to reducing recompaction. Management of a hardsetting soil must include the whole rotation, including when to till, when to crop, and when to graze or not.

Effects of tillage on soil physical properties and root growth of maize in loam and clay in central China

“…Tillage is one of the most effective ways to reduce soil compaction (Daniells 2012). Soil physical properties and crop growth are affected by tillage systems (Mosaddeghi et al 2009).…”

Clay mineralogy and genesis of fragipan in soils from Southeast Brazil

“…The occurrence of cohesive horizons creates problems from a practical point of view, such as seedling emergence, blocking and resistance to root penetration, decreased productivity and greater effort for soil management (Daniells, 2012;Dexter, 2004;Greene et al, 2002;Mullins et al, 1987Mullins et al, , 1990Schjønning and Thomsen, 2013;Young, 1992). Bulk density of fragipan horizons can reach values as high as 1.7 Mg m − 3 (Young, 1992), and root growth and distribution are restricted to the plow layer, owing to the high penetration resistance exhibited in this soil (greater than 6 MPa) (Young et al, 1991).…”

Improving Farming Practices for Sustainable Soil Use in the Humid Tropics and Rainforest Ecosystem Health

“…Unfortunately, under tropical conditions, the improved soil physical conditions that result from tillage are frequently short-lived due to the deterioration of the porous structure and the reconsolidation of the soil at the rootable layer [16]. This process is known as natural reconsolidation, and its rate of occurrence is dependent on the cumulative rainfall and the overall stability of the soil structure.…”

“…In contrast, the continuous use of mulch may increase the labile organic matter fraction responsible for the formation of an ephemeral structure that, in turn, is important for root growth. Thus, overall, this process may enhance soil rootability, uptake, and nutrient use efficiency [16]. Although the use of mulching and the increasing organic matter affect the primary sustainability issues in tropical agrosystems, their effects are limited to the surface layer and have little effect on nutrient availability.…”

“…In the humid tropics, most soils derived from clastic sedimentary rocks with low content of free iron and organic carbon levels tend to undergo hardsetting, which decreases the rootable soil volume and impairs nutrient uptake [16]. Combining irregular precipitation with a high potential evapotranspiration rate leads to repeated cycles of wetting and drying, so penetration strength is one of the principal indicators to evaluate soil quality.…”