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Horticulture 1000
HT1032 - Soils 2 - Soil temperature
Session 7 - Soil temperature
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Soil temperature

The temperature of a soil is important as it affects how fast plants can grow. Soil temperature also affects how quickly plants take up water and nutrients. Clay soils are cold, wet soils. Germination and seedling growth is usually slow.

Because sandy soils don't contain much water but lots of air, they warm up quickly. They are useful for growing early crops.

Soil temperature affects the speed of chemical reactions. Warm temperatures speed up reactions and colder ones slow them down. Soil temperature affects the breakdown of parent material and how fast micro-organisms work. Both are important in adding and returning nutrients to the soil. Soil temperature is influenced by the climate of the area and the season of the year.

Climate and season

In a warm climate or during summer, the soil is full of chemical and physical activity.

Micro-organisms will slow down when it is too hot (above 35°C). Micro-organism also slows down in the middle of winter as the soil is too cold. They become inactive below 6°C. In winter it takes a long time for organic matter to break down in soils in the cooler parts of New Zealand.

Plants are also affected by soil temperature. When the temperature is right for a particular plant its roots will keep growing. If the soil gets too hot or too cold then the uptake of water and the growth of roots will slow up.

Aspect

The slope of the land and the direction that it faces directly affects the temperature of a soil. Sun will fall on north-facing land during the day in both summer and winter.

Slope of the sun

During the winter south-facing slopes will get less sun during the day. The soil on these slopes cools down quickly in the autumn and warms up slowly in the spring. In the middle of summer these areas will have better growth because the soil is not as hot and dry as the soil on a north-facing slope.

Plant cover

Soil covered in plants is protected (insulated) from fast heating or cooling of the soil (temperature fluctuations). In a recently cultivated paddock, soil will heat up quickly during the day, but it will also lose heat quickly once the sun goes down.

Ploughed paddock is not protected from heat fluctuations Cultivated soil
Vegetation protect paddock from heat fluctuations Paddock covered in vegetation

Soil colour

A dark coloured soil with a lot of organic matter in it heats quickly as it absorbs more heat energy.

Soil water

Wet soil will be cooler because it takes a lot of energy to heat water. Wet soils take longer to heat up in spring than soils that are well drained.

Soil depth

Soil temperature at different depths

The deeper you go down in a soil profile the less the soil temperature will fluctuate. Soil is a good insulator. It can take a while for the soil at the bottom of a profile to heat up, but it will also take a longer time for it to lose the heat that is stored there.

Teacher-marked activity

Complete Activity 7A, the teacher-marked activity in your workbook when you have completed the following topics:

Key points   Key points

  • Soil temperature affects the speed of plant growth and soil processes.
  • Soil temperature is influenced by: climate, season, aspect, water levels, soil colour, plant cover and soil depth.
  • The temperature in a soil will determine the speed of chemical and biological activity. Clay soils take a long time to warm up but are also slower to cool down. The temperature in a sandy soil can change rapidly. Wet soils also take longer to warm up.

What's next?

  1. Complete the self-assessment in the back of your workbook.
  2. Return your workbook to your teacher.
  3. Continue with HT1033 - Soils 3.
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