Estimating nitrogen fertilizer requirements of canola (Brassica napus L.) using sensor-based estimates of yield potential and crop response to nitrogen

The challenge in managing nitrogen (N) fertilizer in canola ( Brassica napus L.) production is deciding on application rates that meet but do not exceed the demands of the crop for its specific environment. Crop N requirements depend on their potential yield, the extent of N losses, and the soil's capacity to supply N to the crop; all of which are difficult to quantify and highly variable. Active optical sensors have potential to improve upon our ability to match N inputs with crop demands. We completed several field experiments with canola at various locations in 2005 and 2006 to establish whether current sensing technology and application equipment can be adapted to improve upon our current ability to manage N fertilizer in canola production.; First, we determined whether it was possible to estimate the potential yield of canola using normalized difference vegetation index (NDVI) measurements and the best methods for doing so. We established field experiments with canola where we varied N fertilizer and seeding rates at Brandon. Indian Head, Ottawa, Scott, and Swift Current to achieve a wide range of grain yields. The correlation between NDVI and yield generally remained weak until the canola had five leaves, at which point it improved until peaking at the mid to late-bolting stage and generally became very weak when the canola was in full bloom. When the data from selected sites and sensing dates were compiled, a reasonably strong exponential relationship existed between NDVI and grain yield (R 2 = 0.444). While the best relationship was obtained when we divided NDVI by corn heat units (R2 = 0.562), all the heat units tested performed similarly and dividing NDVI by days from planting was also reasonably effective (R2 = 0.474).; Our next objective was to assess the potential benefits and risks of fine-tuning post-emergent N rates using optical sensors relative to the predominant practice of applying the crop's entire N requirements at seeding. In plot studies at Indian Head and Scott, SK, we evaluated several N management treatments with respect to N fertilizer use (kg N ha-1), canola seed yield (kg ha-1), and agronomic N use efficiency (kg grain kg N applied -1). While we always reduced N use using NDVI measurement to fine-tune N rates in the small plot studies, doing so resulted in substantial yield losses at Indian Head in 2006, where it was very hot and dry late in the season. Agronomic N use-efficiency (ANUE) was increased using the sensor at one site-year and was never lower than in the benchmark treatment. The results were similar in nine large-scale trials with commercial equipment that we completed in cooperation with producers. In most of the on-farm trials, we reduced N fertilizer with no impact on yield, thus likely increasing N use-efficiency in several cases. However, the dollar value of the savings in fertilizer N rarely exceeded the cost of the post-emergent (PE) N application and marginal economic returns for the two treatments were usually similar.; Sensor-based N management appears to be a feasible option for canola production in western Canada and has potential to increase N use-efficiency over the long-term. However, increased efficiency alone will not provide sufficient motivation for producers to adopt this technology and whether or not sensor-based N management is economically advantageous over current practices remains uncertain.