Temperature is one of four main functions controlling plant growth. In addition to temperature; water, nutrients, and light control commencement of growth, rate of growth, and cessation of growth.

Factors which can affect Soil temperature

There are many factors which affect soil temperature and determine how quickly it rises and falls. Much of this variation is due to:

  • Soil type - the sandy and loam based soils generally warm much more quickly than the heaver clay soils
  • Climate and season - In a warm climate or during summer, the soil is full of chemical and physical activity on the flip side in a cold environment limited activity happens in a cool soil
  • Aspect - the slope of the land and the direction that it faces directly affects the temperature of a soil
  • Plant cover – plants offer insulation from fast heating or cooling of the soil
  • Soil Organic Matter – high soil organic matter will buffer temperature extremes, and drive microbial activity, which can provide warmer conditions as soil temperature declines
  • 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.

A factor that is often not considered when looking at soil temperature is that temperature drives microbial function, which in turn drives plant growth. This is an area where farmers can impact the whole system. With optimum microbial activity, you will have improved soil physical conditions, which in turn influences the four main functions of plant growth (temperature, water, nutrients, light), leading to better water movement, air movement, and nutrient movement. These optimal conditions, work to buffer high temperature as well. A soil with good air and water movement, high root biomass, will not overheat to the same extent as a poor soil.

Microbial activity also can generate heat. Therefore if you have high soil microbial activity soil, you will also have a soil that is warmer during cold temperatures, and will actually buffer temperature extremes. This means plant growth will commence earlier in the spring therefore extending the growing season. We have seen that using EM to stimulate the microbial life in the soil has increased the soil temperature in at least one situation. This observation trial was conducted by a market gardener. They applied EM to a strip of soil that they were preparing to plant, and left a strip untreated as a control. They measured a 2 degree increase in the soil temperature where EM was applied.

How to create a biologically active soil

Adding a food source to your soil is one way to stimulate a healthy soil environment. All farmers add organic matter to their system in the form of crop residues and grazing animals (tall grazing) leaving behind a blanket of nutrient-rich waste in the form of dead matter from plants, dead roots, manure etc. Often though there isn’t enough. Other techniques include topping and leaving stubble through to inputs like composts and humates. These products can energise the soil biology and feed the soil rather than just feeding the plant.

Increasing microbial diversity in the soil is also very important. This enhances the breakdown of organic matter with the entire soil food web playing an important role creating a healthier and more active soil environment. In order to get microbial diversity in the soil, we can plant mixed pasture swards, use biologically friendly fertilisers or add biology directly through bio-stimulants or other biological inoculants. EM fits into this category and has the effect of adding billions of beneficial microbes including fungi, bacteria and yeasts while also having a stimulatory effect on resident microbes to keep the engine room of our growing systems firing on all cylinders.