Degree of crop emergence (%), uniformity of emergence and plant stand density were measured. Crop emergence (%) declined with increasing seeding rates. This is an expected trend, since the competition for resources among the emerging seedlings increases with an increase in seeding rates, thus leading to higher seedling mortality. Crop emergence also varied notably between different planters. Emergence (%) for the precision planter (12") was 1.2-1.5 times higher compared to the air drill and 20" planter for seeding rates between 40 to 180 seeds/m2 (Figure 1). Both the planters (12" and 20") led to uniform emergence in 83% of plots across all locations. The air drill had uniform emergence in only 58% of the plots. This trend was consistent at both the irrigated and rainfed locations. The air drill was prone to uneven emergence largely due to variable seeding depth. Differences in seeding depth led to variability in crop developmental stages, such that seeds sown at shallow depth reached the 4-leaf stage while deeper-sown seeds were still at the 2-leaf or cotyledon stage.
Plant density, which measures the number of plants/m² upon crop establishment, also varied between different planters. The three planters did not show any statistically significant difference at the lowest seed rate (20 seeds/m²), but the 12" planter led to a greater increase in plant density compared to other planters at higher seed rates (Figure 1). Plant stand density for the 12" planter exceeded the other seeders by about 5 plants/m² at 40 and 60 seeds/m², approx.10 plants/m² at 80 seeds/m², and 15-20 plants/m² at 160 seeds/m² rate. The trends were similar across irrigated and rainfed locations, with the precision planter (12") leading to higher crop emergence and plant density compared to air drill and precision planter (20") (Figure 1). These data indicate that 12" planter provides a distinct advantage for canola emergence and plant density.
While the competition between plants is low at 20 seeds/m2 rate, the inter-plant competition increases at higher seeding rates. Thus, at higher seeding rates, uniform seed placement and superior depth control provided by the 12" planter leads to higher emergence and plant stand establishment. The 20" planter, on the other hand, does not differ significantly from the air drill in terms of plant emergence and density. This is likely because of the larger inter-row width for 20" planter; more seeds have to be placed in each row to obtain the same seed density as other planters. Thus, higher number of seeds are placed in each row, which increases the competition between plants and is detrimental to early season canola performance.
The effect of different planters on the canopy closure obtained by the crop was of particular interest, since the wider 12" and 20" seed rows are expected to impact the canopy closure obtained by the crop. Canopy closure was estimated using the NDVI and FGCC measurements. NDVI measurements provide a reliable proxy measurement for the photosynthetic activity of the plants. However, extraneous factors such as growth stage of the crop, weed abundance and density, and soil fertility etc. were expected to confound this measurement. The 12" planter also led to higher canopy closure at the irrigated plot in Lethbridge, while the canopy closure at the rainfed plot in Lethbridge was higher for the air drill, thus indicating that that the 12" planter leads to a better canopy cover in increased crop growth conditions (Figure 2).
Across all seed rates, the 20" planter had an average yield of 2114 kg/ha. The air drill and 12" planter by comparison led to an average yield of 2812 and 2972 kg/ha, respectively. Canola yield for the 20" planter was 20-28% less compared to the air drill for different seed rates (Figure 3). The wider rows on the 20" planter led to increased interplant competition throughout the growing season. Furthermore, the wider rows delay canopy closure and limit access to resources such as water, sunlight, and nutrients between the rows.
While the differences in yield between the air drill and 12" planter were statistically non-significant, the 12" planter consistently led to a 2-10 % increase in yield compared to the air drill at all seeding rates (Figure 3). The 12" planter led to an average increase of 160 kg/ha of canola yield, which although small in magnitude, may lead to significant increase in profit across the millions of acres of canola production for the industry.
More importantly, there was a significant difference in the performance of air drill and 12" planter when observed across different cropping conditions. At the irrigated Lethbridge location, the average yield for all planters was higher compared to the rainfed Lethbridge and Medicine Hat locations (Figure 4). However, 12" planter led to a significantly higher yield compared to air drill and 20" planter at the irrigated location, with an increase in average canola yield of 463 kg/ha compared to the air drill and 1584 kg/ha compared to the 20" planter (Figure 4).
At the rainfed locations, the difference in yields between the air drill and 12" planter was not statistically significant, while the 20" planter had a significantly less yield. Similar trends were observed when the canola yield for different planters was observed across the years. During 2016 and 2017, the 12" planter showed a trend of higher yield compared to the air drill for all seed rates (Figure 5). These years had a high cumulative precipitation, with an annual precipitation of 420 and 303 mm at Medicine Hat, and 369 and 278 mm at Lethbridge during 2016 and 2017, respectively.
Conversely, the yields were higher for air drill compared to the planters during 2018, when the annual precipitation was low, with an average annual precipitation of 199.6 mm at Medicine Hat, and 261 mm at Lethbridge. These trends indicate that the 12" planter performs better in the conditions that favor increased crop production, which may be attributed to the precise control of 12" planters on seed placement which helps to reduce interplant competition, thus enabling higher crop production. However, the performance of air drill is comparable to the 12" planter in growth-limited conditions since the inter-plant competition is reduced by limited crop production.
Liquid Phosphorous Study
The major purpose of this trial was to estimate the seed-safe rates of in-row liquid P fertilizer when using precision planters. The data were obtained on plant establishment, growth, and yield parameters similar to the previous trial.
Addition of liquid P at any rate did not affect the plant stand density for the air drill. However, with the precision planters (12" and 20"), plant density at fertilizer rate of 60 kg/ha was lower (Figure 6), thus indicating that high P fertilization rate at 60 kg/ha may have led to some degree of seedling mortality in case of precision planters.
Crop yield did not show any differences amongst the P application rates. When observed across the planters, the air drill and precision planter with 12" spacing showed similar trends with no differences in yield across different liquid P application rates. However, the precision planter with 20" spacing showed lower yield with liquid P application rate of 60 kg/ha, although the differences are not statistically significant (Figure 7). These results in aggregate indicate that higher liquid P application rates (60 kg/ha) may have led to increased seedling mortality in case of precision planters (12" and 20") thus reducing plant stand density at the initial crop establishment phase.
However, crops were able to recover from the initial losses thus leading to no substantial differences between different P rates for crop yield. The recovery may, however, be less effective for the precision planter with 20" spacing compared to the 12" planter, since the 20" planter had lesser crop yield for liquid P application rate of 60 kg/ha compared to other fertilizer rates. The application of liquid P to canola crop at any rate did not improve plant emergence, growth or yield significantly compared to no application of liquid P. Thus, the use of liquid P for canola crop production may be re-evaluated under these conditions.