Prediction of the soil structures produced by tillage

Data are presented for the amount of clods >50 mm produced when five different soils were tilled at a range of different, naturally occurring water contents. The optimum water content for soil tillage is defined as that at which the amount of clods produced is minimum. The amount clods produced at this optimum water content is shown to be linearly and negatively correlated with the value of Dexter's index S of soil physical quality. This results in a rational model for soil tillage that enables predictions to be made for all different soils and conditions. Pedo-transfer functions can be used to estimate the input parameters for the model for cases, for which measured values are not available. It is concluded that for soils with good physical condition (i.e. S > 0.035), no clods >50 mm are produced during tillage.