K. N. Harker

Seeding rate, herbicide timing and competitive hybrids contribute to integrated weed management in canola (Brassica napus)

Implementing a favourable agronomic practice often enhances canola production. Combining several optimal practices may further increase production, and, given greater crop health and competitiveness, could also improve weed control. A field experiment was conducted at Lacombe and Lethbridge, Alberta, from 1998 to 2000, to determine the optimal combination of glufosinate-tolerant cultivar (hybrid InVigor 2153 or open-pollinated Exceed), crop seeding rate (100, 150, or 200 seeds m-2) and time of weed removal (two-, four-, or six-leaf stage of canola) for canola yield and weed suppression. At equal targeted seeding rates, the hybrid cultivar had greater seedling density (8 plants m-2 higher) and seed yield (22% higher) when compared with the open-pollinated cultivar. Combining the better cultivar with the highest seeding rate, and the earliest time of weed removal led to a 41% yield increase compared with the combination of the weaker cultivar, the lowest seeding rate and the latest time of weed removal. The...

Soil microbial biomass and diversity after herbicide application

Greenhouse and field experiments were conducted to investigate the effects of herbicides on soil microbial C (microbial biomass), bacterial diversity and community structure. In the first greenhouse experiment, 12 herbicides were applied at recommended rates to a Gray Luvisolic soil contained in trays. Soil samples were collected 0, 1, 2, 3 and 4 wk after treatment and analysed for microbial C and bacterial diversity. The second greenhouse experiment was similar to the first, but only 6 of the 12 herbicides were applied to a Gray Luvisolic and Black Chernozemic soil. The same six herbicides were applied to the Gray Luvisolic soil at a field site near Fort Vermilion, Alberta, and to the Black Chernozemic soil at Lacombe, Alberta, in 2000. In the first greenhouse experiment, metribuzin, imazamox/imazethapyr, triasulfuron and metsulfuron methyl reduced microbial C compared with glufosinate ammonium and sethoxydim. In the second greenhouse experiment, microbial diversity as determined by Shannon index was low...

Fall and spring seeding date effects on herbicide-tolerant canola (Brassica napus L.) cultivars

More flexible and effective weed control with herbicide-tolerant B. napus canola allows for additional seeding management options, such as fall (dormant) and early spring (ES) seeding. Field experiments were conducted at Lacombe and Beaverlodge (1999–2001), Didsbury (1999–2000), and Lethbridge (2000–2001), Alberta, Canada, primarily to evaluate the effect of fall (late October-November), ES (late April-early May), and normal spring (NS) (ca. mid-May) seeding dates on glufosinate-, glyphosate-, and imidazolinone-tolerant canola development and yield. Fall seeding resulted in 46% lower plant density and nearly double the dockage than spring seeding. ES-seeded canola had 19% higher seed yield and 2.1% higher oil content than fall-seeded canola. ES seeding significantly increased yield compared to fall-seeded canola for 8 of 10 site -years or compared to NS seeding for 4 of 10 site-years; ES-seeded canola equalled the yield of NS-seeded canola for 6 of 10 site-years. Yield response to seeding date did not dif...

Field evaluation of regression equations to estimate crop yield losses due to weeds

Various regression equations based on weed density alone, or relative time of weed and crop emergence or crop density in addition to weed density have been developed in western Canada to estimate the effects of wild oat (Avena fatua L.) and volunteer cereals on yield loss of field crops, and to advise farmers on the economics of weed control with herbicides. In 1997, 1998, and 1999, several of these equations were evaluated in 9 barley (Hordeum vulgare L.), 9 wheat (Triticum aestivum L.) and 11 canola (Brassica napus L.) fields in Alberta. Wild oat was the dominant weed in the barley and wheat fields, and wild oat or volunteer cereals in the canola fields. In barley and wheat, more complex equations based on both weed density and either crop density or relative time of weed and crop emergence were more reliable in estimating yield losses due to wild oat than those based on weed density alone. In canola, an equation based on volunteer barley and canola density provided the most reliable estimates. Under th...

Polymer seed coating of early- and late-fall-seeded herbicide-tolerant canola (Brassica napus L.) cultivars

Polymer seed coatings offer an opportunity to fall seed Brassica napus earlier in October, thus avoiding difficult seeding conditions (wet/frozen soils) common in late October or early November. A multi-year field experiment was conducted at four locations in Alberta, Canada, to investigate the effect of early (mid-October) and late fall (late October-early November) canola seeding with and without a germination-inhibiting polymer seed coat. Yield and yield components were determined in glufosinate (hybrid and open-pollinated), glyphosate (open-pollinated), and imidazolinone (open-pollinated) herbicidetolerant canola cultivars. Early-seeded canola without the polymer coat had a reduced plant density of 58% compared to late-fall-seeded canola. Application of the polymer coat on early-seeded canola increased plant density by 80% compared to uncoated seed. Seed yield and dockage were not affected by seeding date when a polymer seed coating was used. Without the polymer seed coat, canola yield was reduced 42%...

Economic benefits of integrated weed management systems for field crops in the Dark Brown and Black soil zones of western Canada

Integrated weed management (IWM) systems that combine seeding date, seeding rate, herbicide rate, and timing of nitrogen (N) fertilizer application were assessed for their economic performance in the Dark Brown and Black soil zones. A barley-field pea IWM system in the Black soil zone at Lacombe, Alberta, and a wheat-canola IWM system in the Dark Brown soil zone at Lethbridge, Alberta, and Scott, Saskatchewan, were used to assess contributions of seeding date (April or May), seeding rate (recommended or 150% of recommended), fertilizer timing (fall or spring), and in-crop herbicide rate (50% or 100% of recommended). The factorial set of treatments was applied in 4 consecutive years at each site. For barley-field pea production, the highest contribution margin (CM) (returns over variable production costs) was earned with 50% of the recommended herbicide rate, spring application of N fertilizer, seeding barley later at the high seeding rate, and seeding field pea early at the recommended seeding rate. This ...

Influence of N fertilization method on weed growth, grain yield and grain protein concentration in no-till winter wheat.

Applying polymer-coated urea (PCU) instead of uncoated urea may benefit winter wheat (Triticum aestivum L.) production by reducing weed growth or increasing grain yield and protein concentration. Field trials were conducted for 3 yr under rainfed and irrigated conditions in Lethbridge and 2 yr under rainfed conditions in Lacombe to determine potential benefits of substituting urea with PCU for typical winter wheat production practices in Alberta. Four factors were included in each experiment: (1) urea type (urea, PCU and a 50:50 blend of urea and PCU), (2) application method (fall side-band vs. spring broadcast), (3) N rate (1× and 1.5× recommended N rate), and (4) herbicide application (none vs. full). Herbicide application substantially reduced weed biomass at all site-years, but only increased average grain yield by 9%. Dicot weed biomass was not affected by fertilizer treatment, but monocot weed biomass was less for fall banded than spring broadcast application and less for urea than PCU or blend at t...

Canada thistle (Cirsium arvense) management in canola (Brassica rapa) and barley (Hordem vulgare) rotations under zero tillage

The effect of in-crop herbicide rate, crop row spacing and seeding rate on Canada thistle [Cirsium arvense (L.) Scop.] management in two cycles of a canola (Brassica rapa L.)/barley (Hordeum vulgare L.) rotation was investigated under zero tillage at Vegreville, Alberta. The entire plot area received pre-harvest glyphosate from 1993 through 1995. In crop, either no herbicides were applied or clopyralid and dicamba/MCPA-K were applied at one-half or full recommended rates to canola and barley, respectively. In most cases, Canada thistle shoot density and dry weight were lower when the herbicides were used at either rate compared with no herbicide application. Pre-harvest glyphosate followed by either clopyralid or dicamba/MCPA-K in-crop reduced Canada thistle shoot densities from approximately 20 m–2 in 1993 to one or fewer m–2 in 1996. In-crop herbicides resulted in higher crop yields and revenues in 1993 and 1994, but not in 1996 when the Canada thistle infestation was relatively low. The effect of crop ...

Economic evaluation of seeding decisions in hybrid and open-pollinated herbicide-resistant canola (Brassica napus)

Herbicide-resistant canola (Brassica napus) is widely cultivated in western Canada. Data from a multi-year field experiment conducted at three locations in Alberta were used to investigate the effect of canola cultivar, time of seeding, polymer seed coating (PSC) on profitability and the net return risk. Cultivars included hybrid and open pollinated. Time of seeding was early and late fall, and early and normal spring. The hybrid canola generally had higher mean net return than the open-pollinated cultivar. The probability of thin canola stand was higher for fall dormant seeding compared with spring seeding. The use of PSC for early fall dormant seeding reduced the likelihood of thin canola stand, which translated into risk-efficient decision. However, PSC use for late fall seeding had mixed results. Early and normal spring seeding was generally risk-efficient at all locations. In exceptional cases, net returns from late fall dormant seeding (with or without PSC) were similar to that of spring seeding. Re...

Relationship between seeding rate and plant density of hulled and hull-less barley as influenced by seeding depth in a no-tillage system

Field experiments were conducted under no-tillage at three locations in Alberta, Canada over 3 yr to quantify the relationship between barley seeding rate and plant density in a hulled (AC Harper) and hull-less (Peregrine) variety seeded at two depths (2.5 and 6.25 cm). Regression analysis indicated that barley emergence was consistently better with the hulled variety and at the shallower depth. Predictive equations can help determine appropriate hulled and hull-less barley seeding rates required to obtain desired plant densities.Key words: Hordeum vulgare, hulled barley, hull-less barley, predictive equation.