Soil Temperature

Soil temperature is the result of an ongoing energy balance at and below the surface: incoming solar radiation, outgoing longwave radiation, conduction into deeper layers, and latent heat exchange through evaporation. Darker, drier, bare soils generally absorb and lose heat faster than lighter, moist, covered soils.

• Surface temperature responds most quickly to daily weather and cover conditions
• Deeper layers show smaller daily swings and a time lag behind surface conditions
• Seasonal patterns are dampened but still present at greater depths

Seed germination requires a minimum soil temperature that varies by species, and planting into soil that is too cold can result in poor or erratic emergence. Root growth, nutrient mineralisation, and microbial activity also respond to soil temperature, generally proceeding faster within a favourable warm range and slowing in cold soil.

Soil temperature is measured directly with soil thermometers inserted to a standard depth, or with buried temperature probes and dataloggers for continuous monitoring. Readings are typically taken at a consistent depth and time of day, since soil temperature varies through the day and with depth.

Growers influence soil temperature indirectly, primarily by managing surface cover and moisture, and by timing field operations to soil conditions rather than the calendar alone. Structures such as greenhouses provide more direct temperature control where warranted.

• Use plastic mulch or row covers to raise soil temperature ahead of early planting in some systems
• Retain crop residue to moderate temperature extremes, at some cost to spring warming speed
• Base planting dates on measured soil temperature at seeding depth rather than the calendar alone