soil

• Water content:

  • Fertile soil allows good drainage while retaining enough water for soil biota survival
• Plant nutrients are absorbed in ionic form dissolved in water
• Soluble materials in fertile soils include macronutrients (nitrogen, phosphorus, potassium) and micronutrients (boron, cobalt, copper, iron, manganese, magnesium)
• Toxic ions like aluminium and heavy metals are adsorbed onto mineral particles to prevent harm to soil organisms
• Air content in aerated soils contributes to fertility
• Fertile soils have high dead organic matter content, releasing plant nutrients as it decomposes and providing food for soil biota
• The pH of fertile soils is usually in the range pH 5.5 to pH 7.0, suitable for most plants and soil biota
• Soil biota play a crucial role in soil fertility, including detritivores, decomposers, nitrogen-fixing bacteria, nitrifying bacteria, and mycorrhizal fungi
• Soil texture and structure, with crumb peds improving fertility and platy peds reducing fertility
• Soil depth affects waterlogging and root anchorage
• Aeration by ploughing and drainage increases aerobic conditions, enhancing nitrogen fixation, nitrification, and decomposition
• Farmers increase soil nutrient levels through inorganic fertilisers, organic matter, or natural processes like bacterial nitrogen fixation
• Irrigation increases soil fertility by providing water for plant growth and nutrient absorption
• Soil compaction from heavy machinery or high livestock densities reduces aeration and increases waterlogging
• Controlling soil pH is important to ensure nutrient solubility and prevent leaching
• Types of soil erosion:
• Wind erosion occurs in dry soils with low clay content, leading to soil loss and potential damage to crops and urban areas
• Water erosion includes rain splash erosion, surface runoff erosion, slumping, landslides, and can be exacerbated by steep gradients
• How vegetation reduces soil erosion:
• Vegetation reduces wind velocity, protects soil from raindrop impact, binds soil particles, and increases water infiltration
• Vegetation removal, ploughing vulnerable soils, overgrazing, reduced soil biota, soil compaction, and cultivating steep slopes all increase erosion risk
• Reduced productivity, sedimentation in rivers and reservoirs, increased atmospheric particulates, and desertification are consequences of accelerated soil erosion
• Long term crops, zero tillage cultivation, contour ploughing, terracing, hedgerows, strip cropping, increasing soil organic matter, and livestock management are effective strategies to reduce soil erosion
• Living organisms involved in soil processes affecting soil fertility
• Detritivores such as beetle larvae, millipedes, woodlice, and slugs break up dead organic matter and release nutrients into the soil
• Worms are detritivores that increase soil drainage and aeration by creating tunnels in the soil
• Decomposers, including bacteria and fungi, break down dead organic matter by secreting digestive enzymes
• Detritivores physically break up dead organic matter and increase its surface area for decomposers
• Nitrogen-fixing bacteria convert gaseous nitrogen into ammonium ions
• Nitrifying bacteria oxidise ammonium ions to nitrite ions then to nitrate ions
• Mycorrhizal fungi form symbiotic relationships with plant roots and aid phosphate uptake by the plants
• Soil texture is controlled by the proportions of different size categories of mineral particles present in the soil
• Water is essential for all organisms that live in the soil, including plants
• Plant nutrients are absorbed in ionic form, dissolved in water
• Fertile soils contain macronutrients such as nitrogen, phosphorus, and potassium, present in ionic form mainly as nitrates, phosphates, and potassium ions
• A fertile soil allows good drainage so it does not become waterlogged but still retains enough water for the survival of the soil biota
• Fertile soils also contain micronutrients, including boron, cobalt, copper, iron, manganese, and magnesium
• In a fertile soil, toxic ions such as aluminium and heavy metals are adsorbed onto the surface of mineral particles, usually clay, so they cannot dissolve in the water where they could harm soil organisms
• Soil particles form aggregates called peds
• Particles are bound together by:

  • Polysaccharide gums produced by decomposition
  • Fungal hyphae
  • Roots
  • Action of soil iota
  • Hygroscopic clay particles