EXPERIMENT: DOES BLACK PLASTIC WARM THE SOIL?
Posted: Wed Apr 16, 2008 11:09 am
Here are my findings comparing the soil temperature in open ground, under black plastic, clear plastic and under a fleece tunnel:-
The average temperature over the nine days I tested the soil was:
Black plastic 9C
Clear plastic 10.5C
Fleece cloche 10C
Open ground 9.5C
Air temperature 10.5C
On sunny days the open ground warmed faster than ground under black plastic, and as expected was colder than all the covered ground on frosty nights.
The clear plastic closely followed the air temperature, being 1C warmer in dull weather and 1C less in the sun.
On sunny days the soil under clear plastic was up to 3C warmer than under the black plastic.
On frosty days the soil under clear plastic was .5 to 1 degree higher than the black plastic.
The soil under the fleece tunnel was .5 to 1 degree higher than the black plastic over the period of the test, but not as warm as the clear plastic. This was probably because the fleece was a tunnel and not in contact with the soil.
The black plastic was a little warmer than open ground in cold weather but was slow to warm up when it was sunny, and over the period of the test was .5C less than the open ground, 1C less than fleece cloche and 1.5C less than clear plastic.
The weather during the test covered sunshine, 1 day frost and snow, five frosty nights, cool cloudy and rain, very cold winds and intermittent sun and showers. On the whole quite cold, but warm when the sun came out.
The coldest soil temperature recorded was 6.5 under the black plastic when clear was 7 and the highest was 14 under clear plastic when black only reached 11C.
My conclusions are that clear plastic performs much better than black plastic, warming faster and remaining warmer. Black plastic prevents the soil from warming in the sunshine but keeps it slightly warmer than open ground on cold nights.
Open ground warmed much faster than the ground under black plastic and even though it cooled a little more at night, achieved .5C warmer over the test period.
There were only a few degrees difference in temperature between them all, but I think the black plastic would be better for weed suppression and drying the soil ready for seed sowing in wet weather than for warming the soil.
The average temperature over the nine days I tested the soil was:
Black plastic 9C
Clear plastic 10.5C
Fleece cloche 10C
Open ground 9.5C
Air temperature 10.5C
On sunny days the open ground warmed faster than ground under black plastic, and as expected was colder than all the covered ground on frosty nights.
The clear plastic closely followed the air temperature, being 1C warmer in dull weather and 1C less in the sun.
On sunny days the soil under clear plastic was up to 3C warmer than under the black plastic.
On frosty days the soil under clear plastic was .5 to 1 degree higher than the black plastic.
The soil under the fleece tunnel was .5 to 1 degree higher than the black plastic over the period of the test, but not as warm as the clear plastic. This was probably because the fleece was a tunnel and not in contact with the soil.
The black plastic was a little warmer than open ground in cold weather but was slow to warm up when it was sunny, and over the period of the test was .5C less than the open ground, 1C less than fleece cloche and 1.5C less than clear plastic.
The weather during the test covered sunshine, 1 day frost and snow, five frosty nights, cool cloudy and rain, very cold winds and intermittent sun and showers. On the whole quite cold, but warm when the sun came out.
The coldest soil temperature recorded was 6.5 under the black plastic when clear was 7 and the highest was 14 under clear plastic when black only reached 11C.
My conclusions are that clear plastic performs much better than black plastic, warming faster and remaining warmer. Black plastic prevents the soil from warming in the sunshine but keeps it slightly warmer than open ground on cold nights.
Open ground warmed much faster than the ground under black plastic and even though it cooled a little more at night, achieved .5C warmer over the test period.
There were only a few degrees difference in temperature between them all, but I think the black plastic would be better for weed suppression and drying the soil ready for seed sowing in wet weather than for warming the soil.