Sustainable soil health

Soil is Nature's support medium for plant growth, but soils on only 12% of Earth's land area possess the inherent physical requirements to function for long periods as cropland. One-fourth of this land is now moderately to severely degraded, and efforts are now underway to determine the best means to increase their productivity by improving soil health. Soil health is a measure of how well soil functions in retaining water and recycling nutrients to support robust plant growth. Biotechnologies for crop improvement will have reduced effects if crops continue to be grown on degraded soils. Even when water and fertilizer are available, agricultural use of degraded soils often results in inefficient resource use and off-site pollution. Soil quality, a term sometimes used interchangeably with soil health, applies specifically to observable or measurable soil properties that indicate soil health. Although arable soils around the world differ in inherent properties that determine potential productivity, each soil has alterable properties that can be managed to sustain high productivity into the future. Alterable properties include soil organic matter content, root and microbial density, and macroporosity, all of which are highly dependent on maintaining biological diversity and activity in the soil. Because alterable properties undergo drastic changes when native vegetation is removed and land is disturbed for crop production, sustainable soil health involves restoring biological integrity through proper management. This chapter describes how soils are formed, why soils vary in productivity, and how soil quality can be evaluated in the field, in laboratories, and by advanced research facilities. The chapter concludes with a discussion of how soil health can be improved through diversified cropping, use of microbial technologies, and soil management practices that promote beneficial root-microbe interactions.