A study on irrigated orchards in northern Victoria, Australia, on a fine sandy loam over clayey red-brown earth showed soil hardening within 2-3 months after the initial cultivation. This common yet distinct form of soil hardening is termed coalescence. Coalescence is the slow increase in soil hardness which develops during cycles of wetting and drying. The structure of a well-prepared bed of soil that is water-stable and not trafficked changes to one that is hard, although perforated with biopores. These pores facilitate the infiltration of water, drainage, and some growth of roots, but the hard matrix causes root growth and activity to be substantially reduced compared with roots in loose soil and this reduces the productivity of the crop. Coalescence is an important cause of poor responses in productivity to zero and minimum tillage systems of soil management. Isolated examples of soils in the field that remain soft, loose, and porous, after more than 2 years since cultivation were found. This suggests that it might be possible to prevent coalescence. These coalescence-stable soils, in common with virgin soils, have properties that enable them to resist coalescing. High organic matter (>4% w/w total C content) is closely related to zero coalescence.
