WINTE R 2016
AG TECH NO LO G I E S
PRECISION AG U P DATE SOIL 101: KNOW YOUR SOIL TYPES FOR THE MOST EFFECTIVE IRRIGATION DECISIONS Because soil is the plant’s water and food supply, knowing the type of soil you have is critical to providing your crops with the resources they need for optimum growth and yield. When it comes to irrigation, many growers question how much, how long, how fast and how often they need to irrigate. The answers usually involve a combination of soil characteristics, plant growth stage and weather. However, soil type determines how fast water should be applied. Soil is made up of mineral particles weathered out of rock and held together by organic matter. When you look at soil, it appears that the particles touch each other, but in reality there are spaces, called pores, in between. When soil is dry, the pores are filled with air, but after irrigation or rainfall, the pores fill with water. Water is also held on the soil particles through adhesion and cohesion. There are three basic types of soil: sand, silt and clay, but most soils are composed of a combination of the different types. How they mix will determine the texture of the soil, or, in other words, how the soil looks and feels.
SAND within soil is actually small particles of weathered rock. Sand is fairly coarse and loose so water is able to drain through it easily. While this is good for drainage, it is not good for growing plants because sandy soil will not hold water or nutrients. The upside to sandy soil is that it’s light to work with and warms much more quickly in the spring. SILT can be thought of as fine sand, and it will hold water better than sand. If you were to hold a handful of dry silt in your hand, it would feel almost like flour. If you were to add water to the silt in your hand, it would do a fair job of holding the water and feel slick and smooth.
CLAY is very fine-grained soil. Its particles are even smaller than silt, so there is very little space between the fine grains for air or water to circulate. Therefore, clay does not drain well or provide space for plant roots to flourish. Clay soil is cold and takes time to warm in the spring since the water within also has to warm up. Clay soil can be very heavy to work with when it gets dry. Especially during the summer months, it could turn hard and compact, making it difficult to turn. When clay soil is worked while it’s too wet, though, it’s prone to damage.
PARTICLE SIZE AND WATER SOLUBILITY .002 mm
.05 mm
CLAY
SILT
2.0 mm
SAND
In order to irrigate properly, you need to understand the capacity of plant available water in your soil. Depending on the predominate type of particles present in the soil, water will either penetrate and drain quickly (as in coarse-textured soil made up largely of sand) or water will penetrate and drain slowly (as in fine-textured soils made up largely of silt or clay). However, even if you have your soil properly identified by a qualified soil lab, there are still many factors such as compaction, soil depth, layering, or slope that complicate the ability to estimate plant available water capacity.
The professionals at Ag Technologies can help you assess your needs and make the best irrigation decisions for your situation.