soil temperature

Soil temperature and its implications for seeding

In many office settings, a request to adjust the temperature of the shared office space can be met with anything from a cold shoulder, to a lukewarm acknowledgement, or a heated argument. Out in the field, however, nature holds the thermostat and we do not get to make that request. So, when late April or early May arrives, our part of the world warms up and farmers in the Prairies prepare to get out into the fields and start seeding. But we also keep an eye on soil temperature – or we should. We should because although soil temperature is affected by air temperature, it is also influenced by soil moisture, soil colour, slope of the land, and vegetative cover which can vary with different soils.

Planting at the optimal soil temperature helps to ensure the best crop emergence. As temperature increases, germination becomes faster and more uniform. Seeding into cold soils can cause seeds to remain dormant and become more vulnerable to soil pathogens, diseases, and predators. This will ultimately lead to poor or staggered emergence and less-than-ideal plant stands. Reduced plant stands favours weed and pests, and also presents staging issues when timing pesticide or herbicide applications. For most spring-seeded crops, soil temperatures warmer than 10°C are optimum for germination. Various crops, however, will germinate at lower temperatures. The minimum soil temperatures needed for seeds of some common Prairie crops to germinate is shown in Table 1.

Table 1. Minimum soil temperatures needed for germination to begin (source: Saskatchewan Ministry of Agriculture)

Crop Soil temperature (°C)
Mustard 2
Canola 2
Flax 3
Wheat 4
Barley 4
Lentils 5
Peas 5
Soybeans 10

Assessing soil temperature is quite simple. First, you have to know the seeding depth of your crop. Then, using a soil thermometer, measure the soil temperature at this depth in a few areas throughout your field. Take two readings – one in the morning, and again in the evening. Take the average of these two temperatures and repeat this process for two to three days to get a multiple day average.

But should you base your seeding decision on soil temperature alone? Certainly not. Research in Western Canada has shown that early planting leads to increased yield because early-seeded crops will utilize available soil moisture better, avoid heat stress during flowering, and can evade the peak pest and disease period. So, it is important to take other prevailing conditions into consideration and plan to seed early. If you have to seed into colder soils, a good way to lower your risk is to use a seed treatment that can improve emergence in cold soils as well as protect the seed against diseases and pests before emergence. Furthermore, because root growth is slow in cold soils, a seed-placed, low salt index phosphorus product will be ideal in boosting root growth in this kind of environment. Your local SynergyAG rep can help you choose the right products.

-Ikenna Mbakwe, PhD, PAg
Head of Research

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