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Horticulture 1000
HT1033 - Soils 3 - Soil management and plant growth
Drainage
10

Soil management and plant growth

Here are eight soil management practices, with a summary of how soil is affected by each practice and how this affects plant growth.

Adding organic matter

When organic matter like compost or green manure is added to the soil it decomposes down to humus.

How soil is affected

  • Soil becomes a darker colour so it warms up faster in spring and retains its heat in autumn for longer.
  • There is more biological activity.
  • Soil particles form crumbs improving both drainage and aeration.
  • Organic matter holds water like a sponge so   it is available for plants.
  • Organic matter helps to retain nutrients in the soil.
  • As humus decomposes it adds some nutrients to soil water.
  • The organic matter and humus reduces erosion.

Impact on plant growth

  • Warmer soil in spring provides conditions for faster, even, high germination percentage and strong growth of seedlings leading to higher yields.
  • Increased worm activity increases the nutrients available to plant roots and improves the soil structure by increase the total pore spaces in the soil.
  • Plant roots require air for respiration. The process of respiration provides the plant with energy for growth.
  • Nutrients are needed in many plant processes.
  • Increase in water available especially in dryer conditions or sandy/silty soils.
  • The organic matter and humus provides soil structure ideal for the movement of roots through the soil.

Applying effluent

See teaching and learning materials for achievement standard 90160, AHS1.5: Demonstrate knowledge of the impact of primary production management practice on the environment for details.

How soil is affected

Effluent:

  • adds nitrates and other nutrients into the topsoil
  • adds water into the soil
  • adds some organic matter (see organic matter)
  • increases biological organism activity in the soil for example fungi, bacteria and worms.

Impact on plant growth

  • Water is needed for photosynthesis and transpiration.
  • Nutrients are needed for plant processes leading to growth.
  • Organic matter improves soil structure and therefore a balance of air and water to plant roots.

Adding lime

How soil is affected

  • Lime raises the pH of an acidic soil.
  • More nutrients are available to plants in a less acidic soil.
  • Lime flocculates tiny clay particles so crumbs are formed. A crumb structure improves the drainage and aeration of clay soils. A well-drained soil warms up faster in spring.
  • A pH above 6 and a well-drained soil is desirable for beneficial soil organisms including worms.
  • Possible toxicity from excess micronutrients in the soil is prevented.

Impact on plant growth

  • Plant nutrients will be available in soil water if the pH is not too low – pH 6–6.5 for most food crops.
  • Increased worm activity increases the nutrients available to plant roots and improves the soil structure by increase the total pore spaces in the soil

Applying fertiliser

How soil is affected

  • Fertiliser adds nutrients to the soil
  • Additional fertiliser replaces nutrients that are lost from leaching or the removal of a crop at harvest.
  • Soil testing should take place first to determine which nutrients are required.
  • Sulphur fertilisers can lower a high soil pH.

Impact on plant growth

  • Fertiliser provides nutrients which once dissolved in soil water are then available to the plant roots. Nutrients are used in plant processes and therefore plant growth is improved.
  • Additional nitrogen (N) for leaf growth
  • Additional phosphorus (P) for root growth.
  • Additional potassium (K) for flowering and fruiting.

Drainage

How soil is affected

  • Well-drained soil warms up faster in spring and is more likely to retain heat through the autumn. Air is easier to heat than water. Wet soil is cooler because energy is lost through evaporation.
  • If there is a balance of air and water in the soil, plant roots can respire.
  • Well-drained soil improves conditions for worms and other soil organisms.

Impact on plant growth

  • Warmer soils in spring provides conditions for faster, even,  high germination percentage and strong growth of seedlings leading to higher yields
  • A balance of air and water in the soil provides the ideal environment for soil organisms including worms and decomposers leading to improved conditions for plant roots leading to improved plant growth

Cultivation

How soil is affected

Cultivation:

  • keeps weeds under control
  • aerates the soil
  • breaks up crusts and pans to allow water infiltration
  • improves drainage so excess water is removed so there is a balance of air and water in the soil pores
  • breaks up soil into aggregates. This provides a fine tilth contacting soils with seeds and therefore suitable for germination. It also allows roots to move easily through the soil
  • should only be used where necessary to prevent the problems caused by over cultivation.

Impact on plant growth

  • Fewer weeds mean less competition with desirable plants for soil water, nutrients and space, and therefore improved plant growth.
  • Improved soil structure for plant roots allowing water and air to be available and roots to move through the soil, therefore leading to improved plant growth.

Crop rotation

How soil is affected

  • Deep-rooted plants in the rotation move nutrients from the lower part of the soil profile back up to the soil surface.
  • Prevents the build-up of soil-borne diseases and pests by breaking the cycle.
  • Adds organic matter back into the soil.
  • Legumes in the rotation add nitrogen into the soil.
  • Maintains or improves soil structure allowing plant roots to move through the soil.

Impact on plant growth

Crop rotation improves plant/crop growth and yield because:

  • more nutrients including nitrogen are available
  • organic matter levels are maintained in the soil
  • soil structure is maintained and plant roots can move freely through the soil,
  • fewer pests and diseases around to limit growth.

Irrigation

How soil is affected

  • Irrigation adds water into the soil.
  • Nutrients dissolve in the soil water and become available for plant roots to uptake.
  • Soil micro-organisms need water to survive.

Impact on plant growth

  • Water is needed for plant processes including photosynthesis. Photosynthesis is the process where plants make sugars which are then used for energy for growth.
  • Water is required to keep the plant upright (stops wilting) and for transpiration.
  • Plant roots take up nutrients dissolved in soil water.
  • A lack of water leads to reduced plant growth and reduced yields because plant processes are slowed down.

What's next?

  1. Complete the self-assessment form in the back of the workbook.
  2. Return your workbook to your teacher.
Drainage