Chapter 17

Soil Management for Field Crops

Soil Tilth and Management

Tilth refers to a soil’s suitability to support plant growth, or more specifically to support root growth. Soil tilth depends not only on aggregate formation and stability, but also on such factors as bulk density, soil moisture content, degree of aeration, rate of water infiltration, drainage, and capillary water capacity. Topsoil with good tilth is often said to be loose, friable, and well granulated. These soils are composed of small crumbs or aggregates of silt and clay particles. Larger clumps may form from the smaller crumbs. Various size pores form between the various size soil aggregates to create vital pathways for roots, water, and air. Micropores retain water for plant use, while larger pores drain excess water. This porosity extends into the subsoil structure, although blockier than crumb-like, to allow deep roots to access moisture during droughts. Plant root growth, earthworms, and other soil biota naturally build stable aggregated soil structure while contributing organic matter to the soil. Organic matter gives strength to aggregated soil by bonding the aggregates together, retains moisture, and enriches the soil with nutrients.

Soil Friability

A major aspect of tilth is soil friability. Soil friability is a key soil physical property yielding valuable information on the ease of producing a favorable seed bed during tillage operations. Therefore, soil friability is a crucial soil property in relation to the ability of soil to support plant growth and to minimize the energy required for tillage. A friable soil is defined as the tendency of a mass of unconfined soil to disintegrate and crumble under applied stress into a particular size range of smaller fragments. As might be expected, friability changes markedly with changes in soil water content, especially for fine textured soils such as clay loams.

Guidelines for Managing Soil TiIth

Although each soil presents unique problems and opportunities, the following principles are generally relevant to managing soil tilth:

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