Effect of Soil Temperature at Different Planting Dates, and of Residue Management on Soybean
Manitoba Pule & Soybean Growers
Ramona Mohr – Research Scientist, AAFC
Craig Linde – Diversification Specialist, Manitoba Agriculture
James Frey – Diversification Specialist, Manitoba Agriculture
Experiment 1: to determine the effect of soil temperature at different planting dates on soybean growth, yield and quality
Experiment 2: to determine the effect of residue management on soybean growth, yield and quality
Managing the risk of cold temperature damage in soybean crops grown in short-season areas can be most effectively addressed with an integrated approach. Selection of a well-adapted cultivar suited to local growing conditions is key, as are appropriate planting dates and soil temperature conditions. Current provincial recommendations suggest that soybean be planted from May 15th to May 25th, or when the average soil temperature has reached 10 °C, with 18 to 22 °C considered ideal (Manitoba Agriculture 2013). These research findings suggest that delaying planting beyond the recommended window may result in a significant yield penalty and may expose the crop to fall frost damage. The relationship between soil temperature at planting and soybean growth and yield appears to be more complex, however. The potentially damaging effects of chilling injury, which occurs when soybean seed imbibes water of <10 °C particularly during the first 24 hours after planting, is well-recognized, and underlies the recommendation to delay seeding until the average soil temperature has reached 10 °C. However, the current study did not identify a clear relationship between soil temperature at planting and soybean establishment or yield when soil temperatures were >10 °C. While the current research findings suggest that warmer temperatures at planting may occasionally enhance emergence and increase seed yield when soil temperatures at planting are >10 °C, warmer soil temperatures at planting did not consistently enhance crop emergence or translate into higher yields. When soybeans were planted within or near the recommended planting date
window and soil temperatures at planting were above the critical 10 °C, residue management practices like tillage and straw removal that often increased soil temperature to varying degrees (<1 to 5 °C) rarely increased seed yield. In order to better understand the effects of residue management practices on soybean growth and yield under a broader range of conditions, a field study was initiated in fall 2017 which will look at the effect of a range of residue management practices including burning, tillage, stubble height and straw removal on soybean planted before and during the recommended planting date window
The Canadian prairies represent the northern fringe of soybean production in North America. Growing soybean in this region was long considered unlikely because few areas had more than 120 consecutive frost-free days, and temperatures during the frost-free period were too cold for adequate crop development (Burnett et al. 1985).
With the introduction of early-maturing cultivars adapted to Manitoba conditions, the soybean industry in this province has grown rapidly over the past decade. Production has expanded from traditional areas in the Red River Valley to other regions, leading to a record soybean acreage of 2.3 million acres in 2017 (Statistics Canada 2017).
Despite ongoing improvements to soybean cultivars, the short growing season and climate in Manitoba can be a significant production risk for this long-season crop. Frost and near-freezing conditions in spring and fall can damage soybean. Early planting in cool and wet conditions can increase seedling disease and reduce plant stand (NDSU Extension Service 2010). Soil temperature at seeding, together with soil moisture conditions, may impact establishment (Helms et al. 1996a; Helms et al. 1996b; Wuebker et al. 2001).
Potential may exist to reduce the risks associated with cool temperatures, frost and/or near-freezing conditions through management. Selection of well-adapted cultivars suited to short-season areas is critical. However, proper choice of planting date, and management of preceding crop residue, may influence early-season temperatures and therefore crop growth.
A better understanding of the impact of these factors on soybean growth, yield and quality in various regions within Manitoba may help to refine management practices in order to reduce production risk and optimize soybean production.
Planting date: Manitoba recommendations indicate that soybean should be planted from May 15th to May 25th, or when the average soil temperature has reached 10°C, with 18 to 22°C considered ideal (Manitoba Agriculture 2013). North Dakota recommendations suggest that soybeans not be planted earlier than five days before the average date for the last killing frost in order to reduce the risk of spring frost damage (NDSU Extension Service 2010).
Manitoba production data indicates that soybean yield generally decreases with delayed seeding (Manitoba Agricultural Services Corporation 2013), although research suggests this effect may vary among regions in Manitoba. In seeding date trials in the Morden/Carman area conducted from 2006 through 2008, yield was similar for May planting dates but declined with mid-June planting dates (Manitoba Agriculture 2011). At Arborg, yield declined when planting was delayed until late May and declined further when planting was delayed until mid-June. Soil temperature at planting may have influenced the results obtained. As well, because a killing frost did not occur until late September in these studies, yield differences among planting dates were likely smaller than if an early fall frost had occurred.
In studies conducted in North Dakota, early planting of late-maturing cultivars (Maturity Group I and II) did not increase yield, but early planting of early-maturing cultivars (Maturity Group 0) that were adapted to the region increased yield when an early fall frost occurred (Halvorson et al. 1995). Although early planting increased the risk of spring frost damage, this approach allowed the option of re-planting.
Effect of residue management: Soybean may be grown under a range of cultural practices, from conventional to reduced tillage systems (NDSU Extension Service 2010). Residue management practices may influence the micro-environment the crop is exposed to, both above and below the soil surface. In field studies near Brandon, MB, the effect of wheat residue management (short stubble, tall stubble, cultivated) on canola, pea and wheat was assessed from 2000-02 (Volkmar and Irvine 2003). In this study, stubble delayed day-time soil warming and night-time cooling at the soil surface and at a depth of 7.5 cm, and generally increased day-time and decreased night-time air temperature compared to the cultivated treatment. Stubble treatments also typically had higher soil moisture levels than the cultivated soil. Although these micro-environment effects contributed to increased emergence and vegetative growth, especially for tall stubble, there was minimal effect on crop yield. Little information is available regarding the effect of stubble management on soybean in Manitoba.
Another aspect of residue management that could potentially affect crop growth relates to the type of residue. Anecdotal information suggest that, in the case of canola, direct seeding into oat stubble may sometimes slow emergence and increase the risk of frost damage compared to other cereal stubble types. This effect has been attributed to the “brightness” of the oat straw relative to other cereals, which may reflect more incident light and result in cooler soil and air temperatures near the soil surface. This effect has not been documented in Manitoba however.