Interactions of Rotations and Tillage Systems

Byron Irvine, Doug Derksen, Alan Moulin, Debbie McLaren, Cynthia Grant and Karl Volkmar

Previous meetings of this and other conservation groups have heard many presentations on the value of reduced tillage systems. Not only does low disturbance seeding reduce soil erosion but may reduce evaporation in drier locations such that it is possible to grow crops without fallow in areas where fallow was common. Thus there has been a major uptake of low disturbance seeding in the thin black and dark brown soils of Saskatchewan with a concurrent reduction in summerfallow.

This presentation will highlight 3 studies being conducted at Brandon. The first trial compares placement and timing of nitrogen fertilizer to seeding with sweeps. The second trial, which is in its third year, examines the impact of Strategic Tillage. The concept of Strategic Tillage is to till at specific locations in an otherwise low disturbance rotation to aid in disease and weed management. The third trial, also in its third year, evaluates how altering seeding date and rotation can be used to manage weeds. The last two trials are not complete and as such the information must be viewed with caution.

Comparison of fertilizer placement and timing on weed management using less than recommended herbicide rates (CFI trial)

This trial was planted using a twelve-foot wide ConservaPak drill with plots 24 x 50 feet. All fertilizer treatments in this wheat-canola rotation had 100% and 66% of the recommended herbicide rate applied. Roundup was applied to canola and Horizon and Target applied to wheat. The fertilizer treatments were: fall banding of nitrogen, spring banding of nitrogen, single pass sidebanding of nitrogen with 9" row spacing, single pass sidebanding of nitrogen with 12" row spacing and spring banding of nitrogen followed by seeding with sweeps (high disturbance seeding).

The fall banding treatment often had more weeds presumably due to soil disturbance and the direct effect of nitrogen (Table 1). This effect would not have been a problem if the weeds were annuals however over time these tended to be sow thistle. Over time, the high disturbance (sweep seeding system) was weedier than the other systems.

While fall banding had more weeds than spring banding it and the nine-inch spring sideband treatments had the highest yields (Table 2). The yield of canola was lower when sweeps were used to plant the crop. The twelve-inch row spacing, with sidebanded urea, had lower yields than the nine-inch row spacing. The twelve inch row spacing had low plant populations presumably due to higher with row competition and fertilizer damage from the sidebanded fertilizer. Due to the wider row spacing the fertilizer band is more concentrated and can cause greater damage. Over the 5 years of the trial the high and low herbicide rates had the same yields in both wheat and canola.

Strategic Tillage Trial

This trial was planted using a 12-foot wide ConservaPak drill with nine-inch row spacing; plots were one seeder width and 50 feet long. Urea nitrogen and monoammonium phosphorous were sidebanded to all crops at soil test levels except for pea, which received only phosphorus. All plots received an annual broadcast application of sulfur. Invigor 2573 canola, AC Cora wheat, Carneval pea, and Norlin flax were planted at recommended rates. The high disturbance plots were cultivated twice in the spring just before planting. Heavy harrow and Phoenix harrows were used in the fall before seeding. Herbicides are applied at recommended rates but no fungicides are applied to the crop.

In the strategic tillage trial mean weed numbers were highest when disturbance occurred in the current year (table 3). The continuous heavy harrow treatment had slightly higher weed numbers than the continuous low disturbance treatment. The number of wild oats present prior to spraying was greatest when disturbance with a heavy duty cultivator occurred in the current season (table 4). Wild oat numbers were less than 50% of the low disturbance treatment when cultivation had occurred in the year previous to current crop. In 2000 the high disturbance plots had much greater wild oat numbers indicating that the high disturbance treatment depleted wild oat numbers. The heavy harrow and low disturbance plots had similar weed numbers in the residual counts (table 5). While these numbers were 20-25% lower the overall impact is limited except for wild oat where residual counts over all crops were about 35% of the low disturbance plots (table 6).

High winds and wet soils delayed spraying in 2001 and may have contributed to the lower yields in high disturbance canola, flax and pea (table 7). This is different than in 2000 when canola and pea yields were the same under high disturbance and low disturbance. Low yields in canola on flax where disturbance was high in the previous year was due to very low yields of one plot due to Canada thistle. Soil moisture was monitored hourly throughout the season in the flax plots and no differences in soil moisture were detected. This suggests that yield reductions may have been due to the impact of higher weed numbers and delayed control. Further evidence for this is that wheat yields were similar at all disturbance levels, with wheat being a more competitive crop. Preliminary assessment of this trial suggests that tillage does not destroy the positive effects on long term zero tillage and in fact may reduce total weed numbers and wild oats in the year following tillage. Control of dandelions and Canada has been a problem in flax crops and will force a change to Flax Max from Buctril M and Select.

Scelerotinia and blackleg levels have been low in all treatments with no significant trends in 2001 or 2000. Effect has been found for fusarium in wheat. There has been no "pulse benefit" of planting canola on pea vs. flax in 2000 or 2001 with similar yields on both stubbles.

Management of Weeds by Altering Rotation and Seeding Date

Crops were planted in plots 24 x 50 feet using a 12-foot wide ConservaPak with 9-inch row spacing. Minimum tillage in this trial consists of a fall and spring tillage with a heavy duty cultivator. Nitrogen and phosphorus are sidebanded on all crops except pea, which received only sidebanded phosphorus. Canola plots received an application of broadcast ammonium sulfate. The crop rotations are outlined in table eight. The crops are seeded at various times with winter cereals and dormant canola are planted previous fall, pea as soon as the soil can be worked, then spring wheat, spring canola, and finally proso millet around June 1 and millet after the winter cereal crop has been harvested for forage in rotation six. Dormant seeded canola received only one application of Roundup while the spring seed canola had a pre-plant burn-off and an in-crop application.

Overall weed counts are higher in minimum tillage but this did not translate into yield reductions (Figs 1 and 3). Rotation six, which has only one wild herbicide application, had the lowest pre-spray weed counts under both zero tillage and minimum tillage. Residual weed counts in this rotation were similar to other rotations (Fig 2). The take home message is similar to other studies which show that annual and perennial forages have the potential to reduce weed control costs and are attractive options if a market for the forage is available.

Rotations four and five have the highest residual weed counts perhaps reflecting the low levels of weed chemical weed control and no removal of weeds in a forage crop (Fig 2). Rotations four and five had the lowest pea yields (Fig 3). Despite only having one application of Roundup dormant seeded canola out yielded canola planted in mid May by over 25%. This differs from 2000 when yields of dormant canola were lower due to poor stands and lack of heat stress at the mid-May planting date. While dormant seeding is still risky there appears to be potential for improving yield and weed management.

An interesting observation in 2001 was that winter wheat yields were 9% higher in rotations where tillage had occurred in other years of the rotation. In this study the minimum tillage plots are actually a form of strategic tillage rotations 2-6 since dormant and winter wheat are planted using low disturbance planting. Further work is required to determine the long term impacts of this form of management on soil quality in the moist black soils of the Parkland.

Table 3: Summary of total weed counts (Pre-Spray) Strategic Tillage Trial 2001.

HD1= high disturbance in 2000; HD2= high disturbance in 2001; HH= heavy harrow; PH1= Phoenix harrows in 2000; PH2= Phoenix harrows in 2001; LD= low disturbance; w= wheat; f= flax; c= canola; p= pea; bold is the previous crop

Table 4: Summary of Wild Oat counts (Pre-Spray) Strategic Tillage Trial 2001.

HD1= high disturbance in 2000; HD2= high disturbance in 2001; HH= heavy harrow; PH1= Phoenix harrows in 2000; PH2= Phoenix harrows in 2001; LD= low disturbance; w= wheat; f= flax; c= canola; p= pea; bold is the previous crop

Table 5: Summary of total weed counts (Residual) Strategic Tillage Trial 2001.

HD1= high disturbance in 2000; HD2= high disturbance in 2001; HH= heavy harrow; PH1= Phoenix harrows in 2000; PH2= Phoenix harrows in 2001; LD= low disturbance; w= wheat; f= flax; c= canola; p= pea; bold is the previous crop

Table 6: Summary of Wild Oat counts (Residual) Strategic Tillage Trial 2001.

HD1= high disturbance in 2000; HD2= high disturbance in 2001; HH= heavy harrow; PH1= Phoenix harrows in 2000; PH2= Phoenix harrows in 2001; LD= low disturbance; w= wheat; f= flax; c= canola; p= pea; bold is the previous crop

Table 7: Summary of Seed yields Strategic Tillage Trial 2001.

HD1= high disturbance in 2000; HD2= high disturbance in 2001; HH= heavy harrow; PH1= Phoenix harrows in 2000; PH2= Phoenix harrows in 2001;

LD= low disturbance; w= wheat; f= flax; c= canola; p= pea; bold is the previous crop