SOIL-WATER BASICS & SOIL HEALTH
Knowing your soil and building its health can lead to more effective and efficient irrigation management.
T
he properties of the soil play a crucial role in where irrigation water goes. Some soil properties, like soil texture, are inherent to the soil type present in the field and cannot be changed by management.
Understanding implications of inherent soil properties on water movement and storage can guide irrigation management. Other soil properties, like soil structure and soil organic matter content, can be improved by adopting practices that build soil health. Improving these dynamic soil properties can help increase the water available to the plant in the long run.
How do soil properties affect water infiltration & retention?
Soil texture reflects the relative proportion of clay, silt and sand particles. Finer-textured soils have smaller pores but a greater total pore space compared to coarser-textured soils. The small pores exert capillary forces and can hold onto water against gravity. This is known as field capacity, and the volume of water held in the soil is different based on the soil texture. The capillary forces will also cause water to move in all directions in the soil.
When using drip irrigation on a fine-textured soil, the wetting pattern will be wider, and downward water movement will be slower compared to that in a coarse-textured soil (see fig. 1). Because of the greater total pore space and the greater percentage
BY CHARLOTTE DECOCK, PHD, AND FRANKLIN GAUDI, EDD, CAIS, CIC, CID
of small pores, fine-textured soils can hold onto more water. Therefore, fine-textured soils can be irrigated less frequently with larger amounts of water applied at a time compared to coarse- textured soils. On the other hand, water can move much faster through large pores than through small pores, allowing for higher application rates when irrigating coarse-textured soils.
While management cannot change soil texture, water infiltration and retention can be improved by building soil organic matter and soil structure. Soil structure refers to the three-dimensional units that soil particles are organized in. Sand, silt and clay particles bind together with organic matter in units called aggregates. Aggregation improves both
Figure. 1: Typical wetting patterns over time in sandy versus clay soils. Source: Colorado State Extension.
UNDERSTAND WHAT’S
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