The number of days each year that are available for soil cultivation depends on the weather, but more specifically on soil consistency (sometimes referred to as the workability of the soil). It also influences the timing and effect of cultivations on the soil.
It is assessed in the field by prodding and handling the soil. A very wet soil can lose its structure and flow like a thick fluid. In this state it has no load-bearing strength to support machinery. As the soil dries out it becomes sticky, then plastic. When plastic the soil is readily moulded. In general, the soil is difficult to work in this condition because it still tends to stick to surfaces, has insufficient load-bearing strength, is readily compacted and is easily smeared by cultivating equipment. As the soil dries further it becomes friable. At this stage it is in the ideal state for cultivation because it has adequate load-bearing strength, but the soil aggregates readily crumble. If the soil dries out further to a harsh (or hard) consistency the load-bearing strength improves considerably, but whilst coarse sands and loams still readily crumble in this condition, soils with high clay, silt or fine sand content form hard resistant clods. The friable range can be extended by adding organic matter (see humus). At a time when bulky organic matter is more difficult to obtain it is important to note that a fall in soil humus content narrows the friable range. This allows less latitude in the timing of cultivations and increases the chances of cultivations being undertaken when they damage the soil structure.
Whereas many sands and silts can be cultivated at field capacity, clays and clay loams do not become friable until they have dried out to well below field capacity, i.e. heavier soils need more time for evaporation to remove water through the soil surface.
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