Temperature – How cold is too cold?

Following on the theme of soil (moisture) sensors, this blog is concentrating on soil temperature.  At this time of the year (mid-August) soil temperature is or has become the most important factor influencing irrigation (and to a lesser degree fertiliser application).  Just like soil moisture, if you don’t get the installation or measurement point this right you will never get any decent data and never be able to utilise the soil temperature measurements with any confidence.  There are three key requirements for soil temperature measurement:

a)     Ensure any sensor is centred at 10cm depth or the measurement is taken at 10cm;

b)     Ensure the sensor or measurement taken is under the crop/pasture (not in a bare patch for example); and

c)     Temperature is measured at 9am (and not 9am daylight saving time).

Why is 10cm depth and 9am so important?  Crop production models use the 9am 10cm soil temperature as a key input parameter.  If the soil temperature is not above the base temperature at 9am then production will be affected.

It is imperative you measure soil temperature on your farm and in the paddocks of interest.  As at mid-August there is a wide range in soil temperature.  On the east coast of both islands the temperature gradient is large – warm enough for pasture growth in the North Island and too cold in the South Island.

In the northern east coast of the North Island (Gisborne area) temperatures have already peaked above the base temperature for pasture at 15°C and have been above 10°C for 6 days in August.

In the South Island (in the example mid Canterbury) temperatures have not even approached the 10°C base temperature.

So whether you have soil moisture sensors installed that also measure soil temperature or you use a $50 manual gauge, measure soil temperature from now to assist and guide the need to irrigate.

For more information on anything in this blog please contact HydroServices