In reply to the question about swathed canola tolerating frost better than standing crop: if frost occurs 2-3 days after swathing canola, the green seed problem will be less than in standing crop because the swathing accelerated the drydown probably by 5% or more compared to standing crop. The lower seed moisture content is less affected by ice crystals which injure the enzymes that "degreen" the chlorophyll.
In contrast, if frost occurs the night/morning after swathing, the seed moisture content is still similar to standing crop and thus vulnerability to frost is similar.
This is based on research in the early 1990's where frost cabinets were placed over canola in the field. If the canola was exposed to 2 hours of -3C frost at 10-20% seed color change, then seed chlorophyll was lower only if swathed 48 hours prior. Similarly, if canola was subjected to -7C frost at 30-40% seed color change, swathing had to occur at least 48 hours prior to lower seed chlorophyll.
The maximum rate of chlorophyll degreening occurs with warm temperatures and high seed moisture (35-60%). Remember that canola pods differ in maturity and thus seed moisture content. Thus at an average 20-30% seed moisture content, there is a significant amount of high moisture seed that can still degreen.
The temperature differences between swathed and standing crop is complex. An Alberta Agriculture study some 20 years ago measured differences between swathed and standing cereals. The surface of the swath was about 2 degree C colder than the standing crop at head level. Thus, canola pods near the surface of a swath are more prone to frost damage than the pods within a standing crop canopy. However, pods near the top in a standing crop are the most immature with higher moisture contents and thus most vulnerable to frost damage.
In contrast, if frost occurs the night/morning after swathing, the seed moisture content is still similar to standing crop and thus vulnerability to frost is similar.
This is based on research in the early 1990's where frost cabinets were placed over canola in the field. If the canola was exposed to 2 hours of -3C frost at 10-20% seed color change, then seed chlorophyll was lower only if swathed 48 hours prior. Similarly, if canola was subjected to -7C frost at 30-40% seed color change, swathing had to occur at least 48 hours prior to lower seed chlorophyll.
The maximum rate of chlorophyll degreening occurs with warm temperatures and high seed moisture (35-60%). Remember that canola pods differ in maturity and thus seed moisture content. Thus at an average 20-30% seed moisture content, there is a significant amount of high moisture seed that can still degreen.
The temperature differences between swathed and standing crop is complex. An Alberta Agriculture study some 20 years ago measured differences between swathed and standing cereals. The surface of the swath was about 2 degree C colder than the standing crop at head level. Thus, canola pods near the surface of a swath are more prone to frost damage than the pods within a standing crop canopy. However, pods near the top in a standing crop are the most immature with higher moisture contents and thus most vulnerable to frost damage.
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