Every successful agricultural business relies on the soil. It provides vital minerals for plant development and holds water and nutrients for growth.
Soil is an organic material on earth’s uppermost layer. It contains various minerals, nutrients, water, organic & inorganic particles, and residues of plants & animals.
How is soil formed?
Soil is formed over thousands of years by the weathering of rocks. Weathering is when rain, floods, thunderstorms, hurricanes, tornadoes, etc, physically break the rocks down into small particles. These small particles are mixed with organic matter (anything that was alive that is now decaying in the soil) and that is how soil is made.
Soil takes around 500 years to create just an inch of the upper layer. Because soil is made up of many materials and compositions, the ratio of these determines its formation, colours, and textures.
Which type of soil do you have?
Typically, soil is composed of 5% organic matter, 25% air, 25% of water and 45% of minerals. The exact composition is affected by how it was formed and results in a variation of colours and textures in different locations.
In this blog, we’ll talk about the qualities of the four basic types of soil: sand, silt, clay, and loam and discuss how you can use knowing your soil type to your advantage when deciding what to grow and how to irrigate.
Before writing this blog, we posted a poll on our Facebook and Instagram accounts – we wanted to know what the most common type of soil was from our followers. From those that responded we found that the most common soil was loamy, with 47%, next was sandy with 30%, then clay with 23%. None of our followers reported having silt soil.
If you want to get involved, you can still give us your vote on the poll via Facebook.
How to find out your soil type
If you don’t know your soil type, you can send a sample to be tested by an agronomist, or you can quickly get a rough idea by assessing your soil texture by hand.
Rub a moist (not wet) sample of soil between your forefinger and thumb or firmly squeeze a moist soil sample in your hand. Whilst doing this, assess how it feels…
- Clay soil is sticky and will hold its shape. It retains moisture and nutrients, but has poor drainage and can impede root penetration when too compact or dry.
- Sandy soil feels gritty and will fall apart when opening your hand. It drains well, but is low in nutrients and requires more fertiliser.
- Silty soil feels smooth or slippery and will hold its shape, but not as stubbornly as clay. It has larger particles than clay and smaller particles than sand, so it combines the characteristics of clay and sandy soils.
- Loamy soil is a blend of all soil textures and so holds its shape, but crumbles when lightly poked. Its soil is a perfect combination of clay, sand, and silt.
Look at the triangle diagram, it describes the relative proportions of sand, silt and clay in various types of soils.
Soils with the finest texture are called clay soils, whilst soils with the coarsest texture are called sands. However, a soil that has a relatively even mixture of sand, silt, and clay and exhibits the properties from each is called a loam. There are different types of loams, based upon how much of each constituent is present.
Clay Soil
Clay particles are the smallest of all soil particles, measuring less than 0.002mm in size, this soil does not contain much organic matter.
Clay soil is often dense and as a result has very good water storage qualities and makes it hard for moisture and air to penetrate into it. It will remain wet and cold in the winter and can dry out and crack in the summer.
A good thing about clay soil is that it tends to be more nutrient-rich than other soil types. The reason for this is that the clay soil contains particles, such as calcium, potassium, and magnesium.
What grows well in clay soil?
Clay soil is ideal for moisture-loving plants, such as broccoli, brussels sprouts, cabbage, cauliflower, kale, beans, peas, potatoes and radishes.
Clay soil challenges
Because of their small particle size clay soils can become easily compacted and, as a result, roots can struggle to penetrate the soil. To reduce compaction and to help your farm to thrive, it is a good idea to add in more organic matter and a little sand. Great examples of organic matter to mix in are composted leaves, grass clippings, plant-based kitchen scraps or manure.
This helps to make your soil more of a loan which has better fertility.
Sandy soil
Sand soil particles range from 0.05 to 2.0mm. Sandy soil is light, dry and tends to be acidic and low in nutrients.
When compared to other types of soil, sandy soil has comparatively big particles. Sandy soils, which are common in desert environments, warm rapidly in the heat and hold less moisture and nutrients than other soil types.
What grows well in sandy soil?
Sandy soils are suitable for crops such as carrots, radishes, potatoes, lettuce, collard greens, tomatoes, courgettes (zucchini), corn and herbs such as thyme, rosemary and oregano.
Sandy soil challenges
The challenges with sandy soils come from their lack of moisture and nutrients. There are things you can do to make sandy soil easier to farm:
- Add organic matter (grass cuttings, manure, compost) – this will help with the water-holding capacity of your soil as well as add in nutrients
- Put a thin layer of mulch on top of the soil. Add grass clippings or wood chips to the surface to improve water retention by reducing evaporation.
Silty soil
Silt soil’s particles range from 0.002 to 0.05mm in diameter – halfway between sand and clay, it is a sediment material often occurring on flood lands near rivers. Since silt soils are made up of medium-sized particles, they drain effectively and retain moisture well.
This sort of soil is soft and smooth when there is enough moisture, making it good for growing crops in.
What grows well in silty soil?
Silty soils are softer and lighter than clay soils and don’t compress as easily.
This makes them great for perennial plants, roses and shrubs. However, root vegetables, including parsnips and carrots are a bit harder to grow in this soil as they prefer loose soils which are easier to penetrate – but it is still possible.
Silty soil challenges
Silty soils can lack a solid soil structure and therefore can be prone to erosion.
Tips for improving silty soil
- Add organic matter (compost, manure etc), this adds complexity to the soil structure
- Cover plants with 5-8 cm of mulch (grass clippings or wood chips are great) to help avoid erosion
- Turn over the top level regularly to prevent compaction
Loam Soil
Loamy soils are a balance between different combinations of sand, clay, and silt soils. The best have an approximate ratio of 40% silt, 40% sand, and 20% clay.
A loamy soil is often dark in colour with a mouldable but not sticky texture. The particles have air spaces between them which helps nutrients to travel to the roots of plants. If you have loamy soil you are in luck – it is often regarded as the greatest soil and farmer friendly.
What grows well in loam soil?
This soil usually has good nutrient levels, high water drainage and infiltration capacity and this makes it great for all vegetables.
Vegetables which particularly like a loam soil are wheat, sugarcane, cotton, jute, pulses, and oilseeds.
Getting the best out of your loam soil
As we’ve said, you’ve already lucked out with this soil type, but you may still have some nutrient deficiencies. If you are concerned it is a good idea to get a soil sample tested at a laboratory to determine what its pH and nutrient values are. The results of this test will show you what it would be helpful to add to improve the soil further.
Going for loam…
To get the best general soil for your farm, you should be looking to hit the middle of the soil type triangle. By increasing the volumes of organic matter, such as compost, composted manures, and or sand/silt any soil —even compacted clay —can be transformed into loam.
Irrigating for your soil type
It’s not just the type of crops you can grow that’s impacted by your soil type, you can also get clever with how you water different soils too. Being aware of the specific irrigation patterns best suited to your soil will help your plants to thrive.
As with all farming advice, you have to adapt it to meet your exact situation. Irrigation methods and timings are dependent on your weather, environment, the crops you’re growing etc.
Clay soil has densely packed particles that have little space for water or air. Water is absorbed very slowly and runoff can occur if water is applied too quickly. If you have a high percentage of clay, you want to be looking at watering slowly to allow absorption but it can be infrequent as clay soil will hold water very well and can stay wet for several days.
Sandy soil is very loose and has plenty of space for water or air. Water is absorbed very quickly and runoff usually doesn’t occur. When wet, water tends to move straight down through the soil. Sprinkler and drip irrigation methods work well on sandy soils. You want to water a little and often. Overwatering will simply cause water to run straight through the soil away from the roots.
Silty soil particles hold water, moisture, and nutrients longer than clay or sandy soils. This good water retention means that you can get away with watering infrequently – every few days. Try not to flood your land if you have a silt soil as it may wash away the surface layer. Drip irrigation is well suited to silty soil.
Loam soil has an absorption rate greater than that of clay but not as fast as sandy soil. It will not need watering as frequently as sandy soil, but will not lock in water as much as clay soil.
Irrigation that you can control
Now you have looked into your soil type, it’s important that you have an irrigation set up that allows you to take control of how and when you want to irrigate your specific farm. At Futurepump, we have designed a solar water pump that works well with efficient irrigation application tools such as drip and low-pressure sprinklers to get water slowly and directly to your crops. And because it uses completely free solar energy as power, you can irrigate as and when you need without the worry of fluctuating fuel bills.
At Futurepump we are experts in the manufacture of long-lasting solar irrigation pumps. We want to help smallholder farmers across the world get access to efficient and reliable technologies to grow crops sustainably all year round.
You can find out more about our work and wider mission across futurepump.com
