On Increasing the Depth of Soils

On Increasing The Depth Of Soils by Cuthbert William Johnson. This treatise argues that deepening soil by mechanical means—subsoil ploughing, trenching, or spading—significantly increases crop fertility by improving aeration, moisture supply, and the depth to which roots can extend. Johnson details the Deanstonizing system, introduced by Mr. Smith of Deanston, which breaks the subsoil to about 14–16 inches while keeping the upper soil on the surface; he notes the need for deeper drains and the careful management of timing and labour. He explains two key chemical effects: pulverization allows deeper soil to be penetrated by roots and air, and the soil’s capacity to absorb atmospheric moisture is greatly enhanced in finely divided substrata. Drawing on the testimony of scientific thinkers such as Davy and Saussure and practical farmers like Withers, Rham, Stracey, and Graham, he argues that deep tillage yields lasting benefits in timber plantations and field crops, provided draining and manuring accompany deepening. He also discusses the role of mineral admixtures (chalk, marl, clay) and railways in distributing soil amendments, concluding that soil improvement is essential for sustaining agriculture and national wealth.