REGINA – A well treed farmyard protected from sun and wind is a treat to work in compared to the rigours of an open field.
What humans like about shelter seems to apply to field crops protected by tall stubble.
Research by Herb Cutforth and Brian McConkey of the Agriculture Canada Research Centre in Swift Current, Sask., has found that tall stubble sets up a microclimate at the plant level that allows crops to make the best use of soil moisture.
And that improves yield.
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“It is like a shelterbelt. It is the same principle, just on a smaller scale,” Cutforth said.
Their research indicates that in dry areas such as the brown soil zone, leaving tall stubble, perhaps by cutting with a stripper header, can provide benefits if farmers can successfully sow into such a challenging seed bed.
The Swift Current team compared results in three crops, wheat, canola and a pulse crop, at four stubble heights – cultivated, 15 centimetres, 30 and 45 cm. The study has run for three years and will wind up after the coming season.
The plots all went through winter with tall stubble to equalize the snow trap and spring moisture reserves as much as possible. Shortly before seeding, the team mowed or cultivated the stubble to the various test heights.
They found that water use efficiency and yields increased as stubble height increased.
“There is a bunch of little factors going on and they all add up together to contribute to the plant using water more efficiently, promoting higher yields. Each thing by itself doesn’t really make a difference, but when you add them all together, they affect the plants significantly,” Cutforth said.
Stubble shaded the soil and slowed the wind and these effects were improved as the stubble height increased. The stubble plots had cooler soil than the cultivated plots, but warmer air in the canopy. Overall, tall stubble reduced potential evaporation by more than 25 percent compared to the cultivated stubble.
This was done through a combination of reduced evaporation and plant transpiration.
The good residue on the soil surface reduced evaporation. The tall stubble slowed the wind. This reduced heat loss caused by air movement over the leaves, tending to result in warmer air temperature in the canopy. However, moisture lost through transpiration was lower.
Although the warmer air was not as consistent as the cooler soil, the team believes the warmth would encourage canopy growth, helping to offset the early developmental delay caused by the cooler soil.
Cutforth said cool soil is not a big issue in the Swift Current area, but it would be in more northerly and wetter areas, perhaps causing problems with emergence.
The researchers were surprised that beneficial effects of the stubble appear to improve even with what they called extra tall stubble, 45 cm or taller.
“The fourth year is coming up now and before I start to say this is what is happening, I want to look at (the results of) the fourth year. But there is this tendency, at least up to 20 inch (50 cm) stubble, that the yields continue to increase because of the reduction in evaporation,” he said.
Tall stubble seeding will work only if the producer pays close attention to residue management and has the right seeding equipment.
The straw chopper-spreader on the combine must evenly spread the residue across the width of the header.
The Swift Current team found that generally, hoe type openers such as knife, hoe, spoon or sweeps mounted on a shank are best suited to shorter stubble. Disc openers are better for tall stubble.
Also, precision technology such as the Smart Hitch from Straw Track Manufacturing might help. It uses electronic sensors to follow the seed row contour. They send signals to a controller that hydraulically moves the hitch, guiding the openers between the stubble rows.
