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All healthy soils have similar qualities, like good drainage and a sufficient nutrient supply. But improving the health of your soil is much easier if you know and understand your soil type; it affects how farmers measure and manage the nutrients in the ground.
Soil type is determined by two factors: soil texture (whether the soil’s particles are mostly sand, silt, clay, or a mixture of at least two of the three, which is labeled on a gradient and called loam or loamy) and soil structure (the shape the soil particles take when bound together).
Each soil type presents different benefits and drawbacks. For example, because finer soils (like clay) have more contact between particles, they retain heat longer than coarser soils (like sand), which has implications for chemical and biological activity.
In fact, everything from porosity to aeration varies according to soil type, so knowing yours is key to your farm’s overall productivity and provides a clue as to the type of readings you’ll get about your soil and the sorts of actions to take based on those readings.
Everything from porosity to aeration varies according to soil type, so knowing yours is key to your farm’s overall productivity.
Defined by a composition that’s at least 50 percent sand particles, sandy loam is balanced by varying concentrations of clay and silt. It has a somewhat gritty texture, depending on the ratio of sand to clay and silt, and should form a one- to two-inch-long ribbon that breaks easily when mixed with water and squeezed between two fingers. Because of the comparatively large size of sand particles, water and air can usually move freely through sandy loam. This helps ensure good drainage without too much nutrient runoff, though it also means that sandy loam soils with less clay can struggle to hold enough water or nutrients.
This soil type contains more than 80 percent sand. In addition to its gritty feel, sand is typically prone to dryness. Grab a handful, and you’ll be able to feel the loose single grains. Squeeze a handful of wet sand, and it will take shape, but crumble apart when touched; this is evidence of its large pores. The large size and rounded shape of sand particles allow for fast water absorption and drainage, as well as effective aeration. It’s also easy to work with and dig through sand, and you can do so earlier in the spring because it’s less susceptible to frost than clay soils. However, because of the air pockets that exist between sand particles, water rushes through sand, washing away vital nutrients.
Clay loam combines about 20 to 40 percent clay with near equal parts sand and silt. It has a medium texture, and it feels somewhat smoother and more powdery that sandier soils. Clay is the smallest of the three soil textures, measuring under .002 millimeters in diameter, and has numerous small pores, which slows down water movement and can lead to oversaturation if not irrigated carefully. Additionally, dry clay has a tendency to form solid chunks or layers, called pans, that are tough to break apart. As a result, clay loam soil can suffer from lack of aeration and root growth. However, clay’s high surface area helps it retain nutrients, so clay loam may need less fertilizer than other types.
Loamy sand feels gritty; it can range from as low as 70 to 85 percent sand, to as much as 85 to 90 percent sand, with the remaining mineral composition silt and clay. About a quarter of the sand is a mix of very coarse, coarse, and medium sand, and less than half is very fine or fine sand. This combination results in soil that is highly permeable to water and air. However, because it doesn’t hold very much water or nutrients, loamy sand tends to need frequent irrigation and fertilization.
Managing soil differs from type to type, because of the qualities elaborated above, which is why it’s useful to take soil type into account when looking at readings and data from soil probes. Each snapshot of the soil can be qualified with information about porosity, water-holding capacity, nutrient-holding capacity, erodibility, and root penetration. This can lead to decisions about soil management that wouldn’t be obvious without the combination of knowledge of soil type and individual data from a farm.
For example, in sandy loam, loamy sand, and sandy soils, low-nutrient readings could mean that the soil needs a boost from organic matter like compost. In sandy soils, the organic matter can change the nature of the particles so that they can hold more nutrients, improving soil fertility.
Sandy soils are also at risk of becoming acidic. This can happen slowly, simply because of irrigation that causes nutrients to leach out of the root zone. Or, it can happen more quickly because of the use of certain fertilizers. The chemistry of acidic soils puts them at risk for aluminum toxicity, and so farmers with acidic soils use lime additions to raise the pH. This is particularly common on the East Coast, where farmers start with soils that are already acidic. Frequent readings of soil pH can give these farmers with sandy soils an early alert both if soils risk becoming too acidic and if the lime application is having the desired effect.
Want to read more about soil types and nutrient management? Have questions about probes and soil types? We’ll be covering more soil types with the specifics of how they affect nutrient retention, soil management, and probe measurements. We want to hear from you as we continue to cover these topics.