Optimum water content for tillage
Encyclopedia
The optimum water content for tillage (OPT) is defined as the moisture
content of soil
at which tillage
produces the largest number of small aggregates.
which is indicative of the soil stability.
The OPT can be determined in relation to the volumetric water content at the lower Plastic Limit of the soil (PL).
Some examples of suggested OPT:
For several soils the OPT has been found to equal 0.9 PL, although there are a number of limitations with the use of the lower plastic limit in determining the optimal moisture content. Firstly it is a property of a moulded soil and not an undisturbed soil in the field and secondly, many sand
y soils are not plastic and do not have a lower plastic limit.
Soil will drain to a water content at which no excessive structural damage will occur on tillage.
Soil will never drain to a water content ideal for tillage
Many clay
soils drain very slowly, and as a result they are usually wetter than PL unless they are dried by water extraction by plant uptake.
under the action of an applied force. This has been found to be maximum at the PL of a soil.
Moisture
Humidity is the amount of moisture the air can hold before it rains. Moisture refers to the presence of a liquid, especially water, often in trace amounts...
content of soil
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
at which tillage
Tillage
Tillage is the agricultural preparation of the soil by mechanical agitation of various types, such as digging, stirring, and overturning. Examples of human-powered tilling methods using hand tools include shovelling, picking, mattock work, hoeing, and raking...
produces the largest number of small aggregates.
Overview
The determination of the OPT is important because if tillage is carried out on fields that are wetter or drier than the OPT many problems can be caused, including soil structural damage, through the production of large clods, and an increase in the content of readily dispersible clayClay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...
which is indicative of the soil stability.
The OPT can be determined in relation to the volumetric water content at the lower Plastic Limit of the soil (PL).
Some examples of suggested OPT:
- On a lateritic sandy loam : 0.77 PL
- On a sandy loam : 0.9 PL
For several soils the OPT has been found to equal 0.9 PL, although there are a number of limitations with the use of the lower plastic limit in determining the optimal moisture content. Firstly it is a property of a moulded soil and not an undisturbed soil in the field and secondly, many sand
Sand
Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...
y soils are not plastic and do not have a lower plastic limit.
Relationships between water content at field capacity (FC) and Plastic Limit(PL)
- When FC < PL
Soil will drain to a water content at which no excessive structural damage will occur on tillage.
- When FC > PL
Soil will never drain to a water content ideal for tillage
Many clay
Clay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...
soils drain very slowly, and as a result they are usually wetter than PL unless they are dried by water extraction by plant uptake.
Soil friability
Soil friability is the tendency of a mass of soil to crumbleCrumble
A crumble is a dish of British and Irish origin that can be made in a sweet or savoury version, depending on ingredients used, although the sweet version is much more common. It also can be traced to American cuisine during the European colonization of the Americas. A sweet variety usually contains...
under the action of an applied force. This has been found to be maximum at the PL of a soil.
See also
- Field capacityField capacityField capacity is the amount of soil moisture or water content held in soil after excess water has drained away and the rate of downward movement has materially decreased, which usually takes place within 2–3 days after a rain or irrigation in pervious soils of uniform structure and texture...
- Plastic limit