By By James Tababa
Soil is a critical component of agriculture. It refers to the loose layer that covers the earth’s surface and is composed of rocks, minerals, and organic matter. Soil is formed by the disintegration and weathering of rocks for an extended period of time. Breaking up of rocks into small pieces is naturally caused by wind, water, erosion, and chemical reactions.
Not all soils are created equal. It may vary depending on its origin, mineral composition, and size. Soil can be classified on texture or particle size composition. Soils are classified into three main categories depending on the size of soil particles – sand, silt, and clay. It can be further categorized into a combination of the three. For example, if clay soil has a high sand component, it is called sandy clay.
Each soil texture has its characteristics, properties, and uses. The classification is essential to agriculture to determine the suitable cultivation, irrigation, and amelioration practices for crops.
Sand
Sand is the soil texture with the largest particle size of 0.05-2 mm. Because of its size, it is less prone to soil erosion than other soil types. Sandy soil has a loose structure and a lot of air space, making it easier to till. However, water quickly drains into the lower layers of the ground. As the water goes down the soil, it also washes away the nutrients. Furthermore, sandy soils often have low pH levels, limiting the crop’s availability of some nutrients and use of fertilizer ineffective. Because of these properties, sandy soils generally have low water and nutrient retention.
Sandy soil has a loose structure and is easy to till (Photo by Kenneth Carpina/Pexels)
Pure sand is usually not ideal for most crops. However, succulent plants like cactus, euphorbia, and sedum can be grown in the sand because they need fast-draining soil.
Crops with fibrous and extended root systems, such as tomatoes, melons, squash, strawberries, lettuce, capsicums, tulips, and hibiscus, can grow well in sandy soil.
Sandy soil enables root development of root crops because of its loose structure. Potatoes, sugar beets, cassava, and sweet potato will grow well in sandy soil. Brassicas like broccoli and cabbage should not be planted in very sandy soil because they require a lot of water and nutrients.
Plenty of organic matter, compost, or clay can be added to improve the soil structure, water-holding capacity, and soil pH of very sandy soils.
Silt
Silt soil contains medium-sized soil particles between 0.002 – 0.05 mm. It has a finer texture and has more water-holding capacity than sand. Silty soil also drains slower than sand. However, the soil compacts when completely dry. When there is enough moisture in silty soil, it is smooth and manageable to till.
Silt is deposited by flowing water (Photo by Reimphoto/Getty Image)
Silt is the most susceptible to erosion from moving water. Water currents mainly carry silt particles away during heavy rains. That is why siltation or accumulation of silt is common near rivers.
Silty soils usually are fertile and have sufficient nutrients enabling most vegetables, grasses, shrubs, and trees to grow. However, it is not recommended for root crops because it compacts easily when it dries. Roots of root crops will only develop partially in compacted soil.
To improve the drainage of silty soil, sand or compost should be added.
Clay
Clay has the smallest size particle of less than 0.002 mm. Because of this, particles cling to each other, making the soil structure heavy and compact when dry and sticky when wet. Soil preparation is difficult, and the use of mechanized tillage is recommended.
Clayey soil. Tillage by heavy machinery (Photo by RuudMorjn/Getty Image)
Clay soil is rich in nutrients. However, most have high pH, limiting some nutrients’ availability to plants.
During heavy rains, clayey soil becomes sticky and waterlogged. Water drains too slowly in this type of soil. Adding organic matter and compost will help reduce compaction and improve drainage and aeration.
In the Philippines, clay soil is preferred in lowland rice farming because lowland rice needs flooded soil. Crops that need firm soil anchorage can grow well in clayey soil, such as broccoli, cabbage, kale, peas, leafy vegetables, fruit trees, and most ornamental crops.
Root crops should not be planted in heavily compacted clayey soil, and crops susceptible to waterlogged conditions, such as cactuses and other succulents.
Loam
Loam is composed of nearly equal parts of sand, silt, and clay. It is the ideal soil for most crops because it has good physical properties for water drainage, aeration, and space for roots to grow freely. It is friable and easy to till. Loam soil can also have a high water-holding capacity.
Garden Soil (Photo by piyaset/Getty Image)
Loam soil has the right pH for all nutrients to be available for plants. Having the optimum pH can make the fertilizers more effective for the crops to absorb.
This soil type is suitable for most vegetables, root crops, fruit crops, flowers, and other ornamental crops.
Identifying soil texture is important in agriculture because it directly affects plant growth. Soil texture determines the ability of the soil to retain water, the ease of air and water flow between the soil spaces, and the intensity of tillage.
To summarize, sand is the easiest to till because of its loose particles. However, it doesn’t retain nutrients and water well. Silty soil feels like flour, soft and smooth. Even though silt possesses sufficient nutrients, it is easily washed away by rain and flood. Clay is sticky, dense, and hard. It is the most difficult soil to till. Even so, clay soil retains water well and has the highest nutrient affinity among the three.
Certain crops prefer specific soil types for optimum growth and yield. If the available soil is not preferred, soil amendments like compost and organic matter can be applied to improve its physical properties to make it more suitable for planting.
READ: Nothing more than feeling: How to determine soil texture by feel and ribbon method
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