Soil Temperature: Tillage vs. Herbicide vs. Sward.


Trial Data - December 2014

By Dr Maarten van Helden.

Maarten is from Bordeaux France and is spending a sabbatical year at the Waite Campus on a research project on the influence of mid-row soil management in grapes on ‘ecosystems’

Maarten reports his trial sites this week:  

"Over the last two (sunny) days I did some INFRA-RED Temperature measurements in all plots to see if leaf temperature and soil temperature were influenced by treatments.

The instrument sued is a simple infra-red thermometer, that records SURFACE temperature (infra-red radiation).
I made measurements of the soil and of the canopy. Each individual measurement was done by aiming the thermometer on the surface to be measured and scanning the temperature during 10 to 15 seconds while walking at about 5km/h.

Measurements were repeated twice, for the canopy once on each side of the row to correct for sun/shade. 
Measurements were made between 13h30 and 16h30. The sun radiation (and therefore soil temperature) is strongly influenced by the time of day...

The soil temperature was always done in the sunny areas (so the area directly warmed by the sun) of the midrow.

Air temperature was between 22 and 27 degrees (estimated).
The mean SOIL temperature is high and clearly different between treatments.

Soil surface temperature is already very warm on days like these, over 65 degrees on tilled soil... when the measurements were done mid-day, the sun at its highest...

Tillage (61,3 degrees) being on average 7,6 degrees warmer than; 

Sward (51,7 degrees) (minimum difference 1,1, maximum 11,4 degrees warmer) and 4,1 degrees warmer than Herbicide (57,2 degrees, minimum difference 1,1, maximum 11,4 degrees warmer).

Herbicide (57,2 degrees) being 3,5 degrees warmer than Sward (minimum -2, maximum +7,6 degrees warmer).

However big differences occur among plots, this will depend on soil type, moment of the day and 'real' ground cover (bare, 'straw', stubble, plants).  

In spite of these huge temperature differences of the soil there is NO significant difference in CANOPY temperature
  • Canopy temperature was only slightly above air temperature.
  • This clearly shows the ability of the plants to regulate their temperature through evapo-transpiration. 
  • Small differences were observed (never more then 2,1 degrees lower or 1,4 degrees higher than 'SWARD)', but these seem to be due to 'normal' variability. 
  • So it seems that the vines are NOT influences by the differences in soil temperature at this point.
  • The small size of the plots might be a handicap since air is moving (there was a slight breeze of wind) so the influence of soil-temperature might not be measurable.
As a reminder, in the case of extreme drought the vine will reduce evapo-transpiration by closing its stomata (and take a 'drooping' aspect). In that case canopy temperature will go up significantly above air temperature. Apparently this is not the case yet. This measurement should be repeated later in the year on a warmer day with even dryer conditions..."


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