When the reality of drought hits a grower off guard, there is at least one sure thing to remember – standing crop stubble offers the best possible chance for recovery. For example, years of studies from Agriculture Canada’s Semiarid Prairie Agricultural Research Centre, near Swift Current, SK., indicate that spring wheat yields are better in tall stubble than cultivated or short stubble. Significantly, the stubble height treatments were imposed immediately before spring seeding, thus all plots wintered under similar, undisturbed stubble conditions. The experiment was conducted over four years in an area where growers usually face two major limitations to grain production – lack of water and soil erosion – not unlike conditions for a good part of Alberta in 2002! A report1 on this study points out some interesting things for drought-stricken farmers to consider.
The report discusses how standing stubble alters the in-crop microclimate of a field and provides a less stressful environment for plant growth. Extensive measurements were collected to determine crop response to soil temperature, evaporation, solar radiation and other possible influences. There were no significant stubble treatment effects on plant population. Data analysis indicated that when averaged over the growing season, tall stubble (approx. 37cm or 15in.) reduced evaporation rates by 25% and short stubble (approx. 16cm or 6in.) by 5%, compared to cultivated stubble. It further states that, of the two main yield components, increased kernel number was directly attributable to taller stubble treatments while kernel weight was independent of stubble height. This points out the value of standing stubble for early plant development (prior to anthesis or flowering), chiefly related to superior water use efficiency.
More to the point, seeding into standing stubble provides a level of assurance that plant establishment and growth are being optimized. Stubble left standing in the fall will address problems associated with drought by protecting the soil from blowing winds and trapping snow for increased water infiltration next spring. Straight-cutting the crop may enhance the effort and reduced tillage practice such as direct seeding compliments it.
In practical terms, elimination of fall tillage operations should be a priority to maximize the snow-trap potential and reduce the risk of soil erosion. Also, any spring tillage should be restricted to low-disturbance fertilizer applications if required, and seeding operations that result in minimal stubble knock down. Satisfactory performance can be achieved from narrow knife or angle-disc openers with on-row packing. The system requires a harvest management plan to adequately distribute or remove chaff and straw (not a problem when drought prevails) and may also entail the use of pre-seeding herbicides to control weeds that rob soil moisture and nutrients while competing with early emerging crops.
Whether or not a prairie farmer believes in this departure from traditional cropping systems, if a bad situation gets worse, continued drought next year could result in less crop being seeded. Given that scenario, the practice of leaving stubble standing tall in the field will look like a smart move to protect the soil. Optimistically, stubble cover next spring will create an advantage for direct seeders.
1 Stubble height effects on microclimate, yield and water use efficiency of spring wheat grown in a semiarid climate on the Canadian prairies –H.W. Cutforth and B.G. McConkey, SPARC March 1997