5.3 soil

rocks and minerals break down into smaller particles by weathering (could be physical, chemical or biological) erosion removes and transport the weathered material as rocks and minerals are broken down, they release nutrients and elements and microorganisms such as bacteria and fungi can use water and air to form a layer of soil soil formation is quite slow and could take thousands of years

maltese soil is alkaline as it is derives from the rocks that are calcareous

soil is a dynamic system comprising mineral particles, detritus, air, water, and living organisms interacting together

mineral particles are mainly sand, silt, and clay and they contain elements such as iron, potassium, magnesium, calcium, and sulphur.

detritus is dead material from organisms such as fallen leaves, manure, dead animals, and other kinds of litter it is important as it is a natural source of nutrients made available be decomposers

it gets the nutrients and acts as an anchor for the plants in the soil

soil fertility refers to how much the soil can provide plants with the required nutrients and water in order for the plants to grow properly and reproduce.

minerals and mineral and mineral holding capacity, water and water-holding capacity, aeration, pH and salinity

Soil minerals are the tiny inorganic particles that make up the solid framework of soil and are formed from broken-down rock (parent material). Mineral holding capacity refers to the soil’s ability to retain water and nutrients, preventing them from leaching away, so plants can use them later. This is largely determined by soil texture—the mix of sand, silt, and clay, with sand being the largest particle and clay being the smallest

plants need water to function and support themselves and it is obtained from the soil to the roots. WHC is how capable a type of soil is at holding water. Sandy soil holds water the least as its pores are quite large, loamy soil rich in silt holds water for around 2 hours. Clay rich soil holds water the most, for 2 days Plants take up nutrients from the soil with water as they are very soluble in water

Aeration refers to the air present in the soil. It provides oxygen to the plant roots and the organisms within the soil such as certain aerobic and nitrogen-fixing bacteria. These microorganisms influence nutrient availability. earthworms and other soil organisms improve aeration as the soil cannot be compact.

Optimum soil acidity and alkalinity allow crops to make better use of soil nutrients. As soil pH decreases (meaning acidity increases), nutrient availability is reduced because many nutrients become more soluble and are easily washed out of the soil through leaching. Acidic soils therefore tend to lose nutrients more quickly. A soil pH of around 6–7 is ideal for most crops, as it is close to neutral and allows maximum nutrient availability. In contrast, very alkaline soils limit nutrient availability because many nutrients do not dissolve easily in alkaline conditions.

sandy soil has particles large in size and therefore its pores are large in space. Its texture is coarse and non-sticky. it has good drainage and thus has a poor water holding capacity. it is best for succulents and cacti

Loamy soil is rich in silt and its particles and pores are medium in size. Its texture is smooth and non-sticky. It is medium in drainage and thus has a medium water holding capacity it is usually the best type of soil for all plants.

clay soil is very fine is size and there is little aeration between the particles therefore it has poor drainage, too. The soil swells and shrinks and gets sticky when wet. However, clay soil has a good water holding capacity and is therefore best for plants that require a lot of water.

it is the process that removes the upper layer of soil from which plants get most of their nutrients and water from.

Soil erosion has been happening naturally for millions of years due to the natural elements such as wind and rain. However, man has amplified this natural process and thus soil erosion happens faster than soil formation such as through urbanisation, construction, deforestation, and even agriculture.

overgrazing as it removes natural vegetation that slows down water flow and velocity and also stabilises soil. deforestation (involves the removal of trees from forests) as the trees that were once holding the soil and reducing the possibility of rain splash and gullying are now cut down. over cultivation (excessive use of agricultural land leading to a reduction in activity in soil) such as by growing the same plants in the same patch of land, or mono cropping results in the same nutrients being depleted and therefore increases the possibility of degradation off-roading and trekking as it compacts soil and results in a decrease in water infiltration and increase run off. they also disturb lichens, fungi, algae and other plants that offer soil protection

gullying is the flow of large amounts over the soil creating large gullies (refer to diagram) silting of water bodies (when sediment and other nutrients end up in water bodies leading to silting) and loss of nutrients and top soil which results in covering of organisms at the bottom of a water body, clogging fish gills, reducing the penetration of light which decreases the photosynthesis process of a plant in the water body and causes eutrophication due to the nutrients such as potassium (K), phosphorus (P), nitrogen (N), and calcium (Ca) in the soil water logging (soil becomes saturated with water) which results in plants dying due to lack of oxygen leading to less stability, and salinisation or desertification which results in the soil drying and therefore increases its chances in eroding climate change results in top soil being more vulnerable to erosion such as an increase in flooding

terracing and double walls as by arranging the fields in steps, the possibility of the soil eroding is lessened especially by adding a boundary. wind breaks — usually trees and shrubs — not only hold the soil together but by adding a barrier, soil erosion through wind is lessened. contour ploughing (see diagram) which involves ploughing furrows along the natural curves and contour lines of sloping fields against the direction of water flow. It reduces water velocity and gives it more time to infiltrate in the soil. Without contour ploughing or ploughing vertically, a gully will form. reducing tillage and ploughing to maximise water infiltration. multicropping such as strip cropping and alternation of land use (check next flashcard for eg) to vary the nutrients in the soil and reduce the use of fertiliser lower use of pesticides makes the soil healthier

alternation of soil: wheat, legumes, potatoes, green vegetables such as broccoli, repeat strip cropping: 1 strip of grains such as wheat, 1 strip legumes such as soybeans, and 1 strip mallow such as cotton, all alternating