Soil Type

Soils have different characteristics that make them unique. Knowing the kind of soil you have helps you determine its strengths and weaknesses. While soil is composed of many elements, the place to begin is with your soil type. You just have to observe the composition of the soil’s particles.

RainMachine allows users to specify a soil type for each zone, allowing for more accurate and efficient watering calculations. Different soil types react differently to water; clay soils tend to experience runoff, while loamy soils may hold water for a long duration, etc. The amount of water content held in the soil after excess water has drained away, and the soil's ability to store water, is referred to as Field Capacity, (measured in inches or millimeters). 

Below are the different soil types RainMachine has to choose from. Choose the type that best reflects the properties of your zones.

	Loam: Soil comprised of almost equal amounts of sand and silt and a little less clay. Of the three components, sand particles are the largest. Sand does not hold onto moisture, but it provides good aeration. On the opposite end, clay particles are much smaller and easily compact. That makes clay a great material for building bricks, but not so great for allowing water, air, and plant roots through. (Field Capacity: 0.74 in)
	Clay: Clay soil is composed of tiny particles that are hard and able to become easily compacted. This compaction makes it difficult to plant or even shovel within the soil.While clay soil can be difficult to work with, it can be beneficial to the growth of certain plants. It is able to hold onto the roots of plants better and provide a more stable environment than many other types of soil. (Field Capacity: 0.54 in)
	Clay Loam: A fine-textured soil that breaks into clods or lumps that are hard when dry. When the moist soil is pinched between the thumb and finger, it will form a thin ribbon that will break readily, barely sustaining its own weight. (Field Capacity: 0.42 in)
	Silty Clay: Silt has larger particles than clay and is mainly inorganic in nature.A silty clay soil has a higher percentage of clay than silt. (Field Capacity: 0.61 in)
	Sandy Loam: Sandy loam soils have a high concentration of sand that gives them a gritty feel. In gardens and lawns, sandy loam soils are capable of quickly draining excess water but can not hold significant amounts of water or nutrients for your plants. Plants grown in this type of soil will require more frequent irrigation and fertilization. (Field Capacity: 0.45 in)
	Loamy Sand: This soil type is normally made up of sand mixed with a majority of silt and clay. Many people prefer loamy sand soil for their gardening because this type of soil normally allows for good drainage. (Field Capacity: 0.35 in)
	Sand: This type of soil is easy to cultivate but, since it allows for more drainage than needed, it is important to water it regularly, especially during summer days. As sandy soils don't allow the water to pool around the roots, they are a good choice for plants that have a tendency to suffer from root decay. (Field Capacity: 0.22 in)

Soil Intake Rate and Field Capacity

In addition to the preset soils, you can input your own "Custom" variables to describe your soil composition:
- Intake Rate (inch/mm per hour)
  Relates to the time required to infiltrate a given quantity of water in a specific soil type. In general, the intake rate of lighter-textured (sandy) soil is higher than that of heavier textured (clay) soil. However, sprinkler irrigation with a very high quantity of water can lead to surface runoff even on sandy soils. The intake rate of the soil under irrigation is affected by many factors such as Soil Texture, Soil Structure, Compaction, Organic Matter, Stratified Soils, Salts in the soil, Water Quality, Sediments in the irrigation water, etc. 
- Field Capacity (%)
  Relates to the amount of soil moisture or water content held in the soil after excess water has drained away and the rate of downward movement has decreased. This usually takes place 2–3 days after rain or irrigation in previous soils of uniform structure and texture.

In the image below (from Natural Resources Conservation Service) there is a representation of the soil textural separation percent of clay, silt, and sand. Based on this separation the Intake Rate and Field Capacity differ from a soil type to another.

How to determine soil type

Texture indicates the relative content of particles of various sizes, such as sand, silt, and clay in the soil. Texture influences the ease with which soil can be worked, the amount of water and air it holds, and the rate at which water can enter and move through the soil.

To find the texture of a soil sample, first separate the fine earth, all particles less than 2 mm, from larger particles such as gravel and stones. Fine earth is a mixture of sand, silt, and clay. You must be sure to use only fine earth to perform the following field tests.

Quick field tests to determine soil texture

To check quickly on the texture of the soil at different depths, here are two very simple tests you can perform.

1. Throw-the-ball test

Take a handful of moist soil and squeeze it into a ball.

Throw the ball into the air about 50 cm and then catch it:

If the ball falls apart, it is soil with too much sand.
If the ball sticks together, it is probably soil with enough clay in it.

The bottle test

How to find the approximate proportions of sand, silt, and clay
This is a simple test which will give you a general idea of the proportions of sand, silt, and clay present in the soil.

Put 5 cm of soil in a bottle and fill it with water.
Stir the water and soil well, put the bottle down, and do not touch it for an hour. At the end of an hour, the water will have cleared and you will see that the larger particles have settled;
- On the surface of the water there may be bits of organic matter floating; - On the top is a layer of clay. If the water is still not clear, it is because some of the finest clay is still mixed with the water; - In the middle is a layer of silt; - At the bottom is a layer of sand; Measure the depth of the sand, silt, and clay and estimate the approximate proportion of each.

The following three types of particles can make up your soil are clay, sand, and silt.
Most soils are a combination of these three particles, but the particle type that dominates dictates many of the properties of your soil.The ratio of these sizes determines soil type: clay, loam, clay-loam, silt-loam, and so on.
The ideal soil is 40% sand, 40% silt, and 20% clay. This mixture is referred to as loam. It takes the best from each soil particle type. It has good water drainage and allows air to infiltrate the soil like sand, but it also holds moisture well and is fertile like silt and clay.

For more information on various tests and methods for determining your soil type, check out this article here.

For more a more detailed and scientific analysis of how soil affects irrigation, we suggest reading this article here from the Plant and Soil Science eLibrary.

References:

http://soils4teachers.org/physical-properties

http://croptechnology.unl.edu/pages/informationmodule.php?idinformationmodule=1130447123&topicorder=3&maxto=13&minto=1