Interactions among soil properties, soil processes, and management outcomes are the subject of this chapter. Soil properties constrain, through supplies of water and nutrients, the type of farming that may be practiced. In turn, soils are altered by farming in ways that affect their long-term value for agriculture. As a result, proper management of soil resources is the key to sustaining agriculture. Here we consider how management affects soil characteristics important for short-term productivity and longer term sustainability with a focus on ability to supply essential plant nutrients and water, and ease of tillage.

Spatial variability

Soil management aims at creating favorable and reasonably uniform conditions for plant growth in all parts of individual fields. Spatial variability of landscapes limits attainment of these goals, and soil profiles are seldom uniform. For optimum management, places with different textures, profile depths, slopes, drainage, and native fertility would be farmed differently. Although potential for within-field variation in soil properties increases with field size, small fields introduce another set of problems related to access roads, fencing, unused headlands, and excessive turning space in mechanized systems. Efficient farming requires compromises between field size and degree of heterogeneity although the tendency has been towards larger field size in mechanized cropping systems. Typical field size in the US Corn Belt, for example, is 30 to 60 ha; in Mato Grosso, Brazil, fields in soybean-based systems are often > 200 ha.