Soil and Plants

• Soil - The layer of the earth's surface in which plants grow and have their roots.
• Soil particles are made up of:

  Sand (large)

  Silt (medium)

  clay (small)
• Humus: Dead remains of plants and animals. They add nutrients to the soil and improve texture
• Water: important to keep the plant alive.

  • Transports essential minerals
  • Removes waste products
  • Needed for chemical reactions e.g photosynthesis
  • Helps cool down the plant
• Air: Provides oxygen needed by the roots for respiration. It is found in spaces between roots
• Dissolved mineral salts: Enter the soil from the surrounding rock or humus. Needed for plant growth.
• Soil organisms: These organisms live in the soil and break down plant and animal waste to form soluble salts. The organisms increase soil fertility and improve the amount of air moving through the soil. They also improve water movement.
• Composition of soil:

  Soil particles

  Humus

  Water

  Air

  Dissolved mineral salts

  Soil organisms
• The formation of soil:

  • Weathering
  • Erosion
  • Colonisation
  • Decomposition
• Weathering: Breaking up and wearing away of parent or bedrock.

  It is sudden, violent movement, as well as sudden cooling of the earth's crust, that causes large rocks to be broken down gradually into smaller pieces.
• Erosion: Large rocks are broken down into small particles by rainwater, seawater, rivers, or streams.
• Colonization: When rain comes, plants inhabit the new soil, these provide food for animals.
• Decomposition: Plants and animals die and decay, the acids formed break down the rocks further to form more soil.
• Soil erosion is the removal of top soil, usually by wind and rain. Valuable nutrients are carried away with the soil.
• De-forestation - removal of the forest
• Poor farming methods - such as burning and lack of humus
• Over-grazing - Animals graze the vegetation very closely leaving little plant cover
• Soil conservation is used to prevent or correct soil erosion.
• Re-forestation: restoration of the forest
• Improve farming methods

  • plant correct crops for soil type
  • replace humus after successive crops
• Space out animals in the pasturelands until the vegetation is restored. Is another way of soil conservation
• Clay soil consists of small particles. It has small air spaces therefore water will take a long time to pass through.
• Clay soil will hold too much water, causing the soil to become waterlogged. It has no air spaces and is short of oxygen, so roots cannot breathe, Plants in this type of soil suffer from root rot.
• Sandy soil consists of large particles. it has large air spaces. Water passes through quickly, carrying valuable nutrients with it. This is called leaching
• Loam soil (garden soil) consists of medium sized particles. It is a balanced mixture of particle sizes, air spaces, and humus content. It retains a moderate amount of water.
• Soil permeability is the ease in which water passes through the soil.
• Soil with larger particles is more permeable what soil with smaller particles
• Plants need minerals in the soil for them to grow well. They enter the soil from natural or artificial fertilizers.
• Natural fertilizers add to the humus content (organic matter) of the soil. They work very slowly. There are two types of natural fertilizers.
• Manure is a type of natural fertilizer. Waste material produced by animals. It is used for healthy growth
• Compost is also another natural fertilizer it is the rotting remains of plants
• Artificial fertilizers are man made sources of the essential nutrients needed by plants.
• Artificial fertilizers contain three elements that are most essential for plant growth.

  Nitrogen (N)

  Phosphorus (P)

  Potassium (K)
• The fertilizers hat containing these are called NPK fertilizers. They work very quickly and are washed out of the soil by the rain.
• Nitrogen is one of the essential elements needed for the healthy growth of plants.
• Nitrates are used by plants for the manufacture for protein and repair of living tissue
• Plants have to absorb nitrogen in a form of nitrates.
• The pathway along which nitrogen travels in nature is called the nitrogen cycle
• The nitrogen cycle

  1. The nitrogen in the air enters the soil
  2. The formed nitrates dissolve in the soil water.
  3. Plants absorb nitrates
  4. Plants use the nitrates to build protein in their living tissue.
  5. Animals eat the plants and use the plant protein to build animal protein
  6. Animals produce waste and plants and animals die. These decay, releasing nitrogen compounds in the soil
  7. Denitrifying bacteria in the soil release nitrogen back into the air.
• Nitrogen enters the soil in the following ways: Lightning and rain allow some nitrogen in the air to dissolve in the rainwater, where it is converted into nitrates.