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 clay 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.
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.