Effect of Stubble Management on Subsequent Crops

By Tim Nerbas, PAg

Conservation Agrologist

Since the time of the Palliser expedition, we have long recognized that a lack of moisture is a way of life on the prairies. In Saskatchewan, snow represents as much as 1/3 of the annual precipitation. Tall stubble not only traps more snow compared to short stubble, but it also decreases evaporation at the soil surface. Several studies have shown that leaving stubble as tall as practical can increase both water use efficiency and grain yield.

While we can do nothing to influence precipitation, there are a number of management techniques that can impact how effectively our crops use the water they receive. Standing stubble increases snow trapping and the amount of snow trapped is directly proportional to the stubble height. Thus, leaving tall standing stubble increases the total water supply to the subsequent crop. Tall standing stubble also aids in reducing both wind speed and solar radiation, which in turn helps reduce evaporation and keep the soil cooler (Cutforth and McConkey, 1997). Yet the tall stubble does not appear to reduce plant photosynthesis.

At Swift Current, seeding wheat into tall (> 30cm) stubble increased grain yield and water use efficiency by approximately 12% compared to wheat seeded into cultivated stubble (Table 1). Standing stubble reduced the evaporative demand for water at the soil surface throughout the growing season. Tall stubble increased the proportion of soil water that was used productively by the crop (as reflected in increased water use efficiency and yield).

Table 1: Grain yield and water use efficiency for spring wheat grown on cultivated, short, and tall stubble at Swift Current through the period 1992 -1995.

* - Numbers followed by the same letter are not significantly different.

In 1999, a three-year study at farm scale was implemented near Swift Current. The objective of the project was to assess the effect of stubble management on the microclimate, water use and seed yield of canola. The first two years of the study showed a significant modification of the microclimate by tall (> 30cm) stubble compared to cultivated plots. Canola seeded into tall stubble with extra nitrogen fertilizer (above soil test levels) was the most efficient in using limited water (Table 2). Canola seeded into tall and short stubble with soil test recommended fertility were the next best. The cultivated plots had the lowest water use efficiencies. Fall seeded or early spring seeded Brassicas used water more efficiently than spring seeded Brassicas.

Table 2: The effect of stubble height and seeding management on the mean seed yield of Argentine canola (c.v. Arrow). The results are mean averages from two years of research at Swift Current (adapted from Cutforth et al., 2000).

* - Numbers followed by the same letter are not significantly different.

Adequately fertilized crops not only use water more efficiently but also tend to be more effective in extracting water and nutrients from the soil (Campbell et al., 1993). Long term tillage research conducted at the Scott Research Station shows that water use efficiencies in direct seeding systems have steadily increased compared to conventional tillage. However it is critical that fertility and weed control needs of the crop are met. Otherwise benefits anticipated from these other management techniques like tall standing stubble will not be met.

The microclimate effect from tall standing stubble is reflected in soil temperatures close to the surface. Soil temperature at the 5-cm depth was always lower in tall stubble treatments versus the cultivated treatment. The differences were most pronounced on the warmest days and during the middle of the day. Results tend to indicate that the stubble management influence on microclimate is most pronounced early in the season. The improved microclimate and greater moisture retention of the tall stubble were cumulatively responsible for the higher yield potential. It should be noted that the advantage of tall stubble decreased with delayed seeding.

Although we continue to farm in a climate where moisture deficiencies are the norm rather than the exception, there are a number of management techniques that can improve our chances for success. Doing everything possible to increase available soil water at seeding, and ensure that it and growing season rainfall are used efficiently, will improve crop yields and the bottom line.

Remember: this is a system and as such, it requires a systems approach to provide the conditions for success.