Irvine: Improving disease management in canola using planned-limited tillage

Date: October 2003
Term: 3 years
Status: Completed
Researcher(s): B. Irvine, D. Mclaren, D. Derksen, and C. Grant, Agriculture and Agri-Food Canada, Brandon, MB
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: n/a

Project Summary

In 1999, there was a trend towards low disturbance seeding and zero tillage systems, and towards shorter crop rotations using canola. Other than the seeding operation, zero-tillers believed that any other tillage operation would destroy many of the benefits of zero tillage. However, for certain diseases such as blackleg and for some weed problems, tillage was a recommended method of control. This three-year trial was established to determine the impact of planned-limited tillage of an established zero tillage site on yields, diseases, nutrient uptake and weed numbers. Overall, the results showed that strategic tillage did not have long term negative impacts on diseases, crop yields, or soil quality and could be used in the sub-humid black soil zone to control difficult weeds or level a rough field.

In 1999, there was a trend towards low disturbance seeding and zero tillage systems. Economic pressures and improved weed control options had also resulted in a trend towards shorter crop rotations using canola. Other than the seeding operation, zero-tillers believed that any other tillage operation would destroy many of the benefits of zero tillage, and that even a single tillage operation would cause serious negative long terms impacts in a zero tillage system. However, for certain diseases such as blackleg and for some weed problems, tillage was a recommended method of control.

This trial was established in 1999 to determine the impact of tillage of an established zero tillage site (since 1999) on yields, disease, nutrient uptake and weed numbers. The study was conducted near Brandon Manitoba with two rotations: canola-wheat-pea and canola-wheat flax grown in 2000, 2001 and 2002. All crops were seeded each year and the varieties included Invigor 2573 canola, Carneval pea, Norlin flax and AC Cora wheat.

The tillage systems used were: (1) continuous low disturbance seeding (LD), (2) strategic tillage where a heavy duty cultivator was used to eliminate weeds just prior to planting once in the 3-year cropping system (HD), (3) continuous low disturbance seeding but with heavy harrowing the previous fall in each year of the 3-year cropping system (HHLD), and (4) Phoenix Harrows in the fall prior to seeding the flax crop only (once in 3 years) (PHX). All crops were seeded with ‘Conservapak’ openers on 9” (22.7cm) centres. High disturbance plots were cultivated twice at a depth of 7-8 cm in the spring prior to seeding. Fertilizer and weed management were according to normal cropping recommendations and treatments were not altered by tillage system.

Diseases

The study showed that neither previous crop nor tillage had significant impacts on blackleg or sclerotinia disease levels in the years of the trial. There were no significant differences between the yield of canola in the rotation with pea and with canola. Sclerotinia levels were the same on pea as on flax stubble. Blackleg levels were low in part because of the high level of genetic resistance. Given the low levels of disease found in this trial, it was difficult to determine whether occasional planned tillage had a major impact on canola diseases.

Yields

The results showed that when averaged over 3 growing seasons, pea, flax and to a lesser degree canola, had lower yields when high disturbance occurred in the year of planting, possibly due to higher weed pressure and the inability to control weeds at an early stage with the pesticides used (Table 1 and 2). However, the year after tillage occurred, yields of all crops except pea were equal to the low disturbance check. This is strong evidence that it is possible to till an area that has been in long term tillage without having long term impacts on crop yields. If strategic tillage is necessary, it would likely be best to do so prior to the wheat crop in the rotation. Tillage prior to wheat would result in yields equal to direct seeding in the first year, compared with lower yields for pea and flax crops. Heavy harrowing and Phoenix rotary harrows in the fall had little or no impact on yield, indicating that these treatments did not sufficiently alter the seedbed.

Weeds

Over the 3 years of the trial, total weeds after tillage increased by an average of 32% compared to the low disturbance treatment in the year of tillage. This trend was similar in the year following tillage. However, the total weed numbers 2 years after tillage were similar in plots that had been tilled and those that had not been tilled. Wild oat and wild buckwheat numbers were lower over all crops when tillage had occurred in the year previous. Canada thistle, sowthistle and dandelion numbers prior to spraying were variable and not associated with a specific treatment.

Overall, the results showed that strategic tillage did not have long term negative impacts on diseases, crop yields or weed pressure. Therefore, tillage could be used in the sub-humid black soil zone to control difficult weeds or level a rough field without long term negative impacts on crop yields, diseases or soil quality.

Soil quality measurements in the fall of 2002

Bulk density (0-5 cm) was not affected by tillage or crop. Penetration resistance (kPa) was similar in high and low intensity tillage at 0-5 cm and 5-10 cm and no significant differences were observed between types of crop stubble.

There was a greater proportion of large aggregates (38 mm to 68.8 mm) under low (LD) compared to high disturbance in the spring of 2001 and the spring of 2002. High disturbance resulted in a correspondingly higher proportion of small aggregates less than 0.5 mm. However, no significant difference was observed in organic carbon and nitrogen of soil aggregates due to tillage or crop.

Tillage and preceding crop had no significant effect on soil organic carbon (%) and total nitrogen (%) at 0-10 cm, 10-20 cm, and 20-30 cm. Tillage intensity (high and low levels) and preceding crops (peas or canola) had no significant effect on phosphate phosphorus (0-10 cm). However nitrate nitrogen (0-10 cm) was higher in high disturbance tillage and following canola. High levels of nitrate nitrogen and ammonium were attributed to residual nitrogen fertilizer.

The study also showed that tillage intensity (high and low levels) and preceding crop (peas, flax or canola) had no significant effect on mineralizable nitrogen and all levels of mineralizable nitrogen were above levels (300 mg kg-1) considered to respond to fertilizer nitrogen.

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