Building Soils for Better Crops, Third Edition

Soil Health, Plant Health, and Pests

Overview

There are few farms in this or any country that are not capable of great improvement.

—LUCIUS D. DAVIS, 1830

SOIL PROPERTIES AND THEIR INTERRELATIONSHIPS

Healthy soils occur when their biological, chemical, and physical conditions are all optimal (figure 8.1), enabling high yields of crops. When this occurs, roots are able to proliferate easily, plentiful water enters and is stored in the soil, the plant has a sufficient nutrient supply, there are no harmful chemicals in the soil, and beneficial organisms are very active and able to keep potentially harmful ones in check as well as stimulate plant growth.

A soil’s various properties are frequently related to one another, and the interrelationships should be kept in mind. For example, when a soil is compacted, there is a loss of the large pore spaces, making it difficult or impossible for some of the larger soil organisms to move or even survive. In addition, compaction may make the soil waterlogged, causing chemical changes such as when nitrate (NO3) is denitrified and lost to the atmosphere as nitrogen gas (N2). When soils contain a lot of sodium, common in arid and semiarid climates, aggregates may break apart and cause the soils to have few pore spaces for air exchange. Plants will grow poorly in a soil that has degraded tilth even if it contains an optimum amount of nutrients. Therefore, to prevent problems and develop soil habitat that is optimal for plants, we can’t just focus on one aspect of soil but must approach crop and soil management from a holistic point of view.

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