Know Your Soil Type : Irrigation Guide

Soil is the primary reservoir for plants from where they intake water though roots for their growth and development.

Based on the particle size distribution, typically the soil is divided into the three main categories; sand, clay and loam. Each type of soil handles water differently and have different water holding capacity.

Sandy soil needs more frequent irrigation than the loamy soil as the sandy soil has less water holding capacity means it can hold less water than the loamy soil.

  

Image Credits: DripWorks

Knowing your soil type helps you in the irrigation scheduling and determining the right amount of watering needs. Here are some quick tests to help determine your soil type.

TEST 1: The Bottle Test

• Put 5 cm of soil in a glass bottle and fill it with water
  
  
  
  
  
• Stir the water and soil well, let it sit for an hour. At the end of an hour, the water will have cleared and you will see that the larger particles have settled.

• At the bottom is a layer of sand, in the middle is a layer of silt and on the top 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.
  
  
  


• Measure the depth of the sand, silt and clay and estimate the approximate proportion of each.
  
  
• Compare the proportion with the USDA particle-size classification to get an idea on the textural class of your soil.
  

Textural classes of soils -Based on the USDA particle-size classification

Common names of soils (General texture)	Sand	Silt	Clay	Textural class
Sandy soils (Coarse texture)	86-100	0-14	0-10	Sand
	70-86	0-30	0-15	Loamy sand
Loamy soils (Moderately coarse texture)	50-70	0-50	0-20	Sandy loam
Loamy soils (Medium texture)	23-52	28-50	7-27	Loam
	20-50	74-88	0-27	Silty loam
	0-20	88-100	0-12	Silt
Loamy soils (Moderately fine texture)	20-45	15-52	27-40	Clay loam
	45-80	0-28	20-35	Sandy clay loam
	0-20	40-73	27-40	Silty clay loam
Clayey soils (Fine texture)	45-65	0-20	35-55	Sandy clay
	0-20	40-60	40-60	Silty clay
	0-45	0-40	40-100	Clay

TEST 2: The Manipulative Test

The manipulative test gives you a better idea of the soil texture. This test must be performed exactly in the sequence described below because, to be successful, each step requires progressively more silt and more clay.

• Take a handful of soil and wet it so that it begins to stick together, but without sticking to your hand;

• Roll the soil sample into a ball about 3 cm in diameter;

• Put the ball down on the floor...

• If it falls apart, it is sand;
• If it sticks together, go on to the next step.
• Roll the ball into a sausage shape, 6-7 cm long ...

• If it does not remain in this form, it is loamy sand;
• If it remains in this shape, go on to the next step.
• Continue to roll the sausage until it reaches 15-16 cm long

• If it does not remain in this shape, it is sandy loam;
• If it remains in this shape, go on to the next step.
• Try to bend the sausage into a half-circle ...

• If you cannot, it is loam;
• If you can, go on to the next step.
• Continue to bend the sausage to form a full circle ...
• If you cannot, it is heavy loam;
• If you can, with slight cracks in the sausage, it is light clay;
• If you can, with no cracks in the sausage, it is clay.

References: 

1- fao.org