Optical sensors have potential for determining nitrogen fertilizer topdressing requirements of canola in Saskatchewan

Abstract

An important challenge in N management is matching fertilizer inputs to crop requirements for specific environmental conditions. Field experiments were completed over 3 yr at two locations in Saskatchewan to evaluate the feasibility of using optical sensors and high-N reference plots along with topdressed liquid urea ammonium-nitrate (UAN) to arrive at more optimal N rates for canola (Brassica napus L.). Treatments included N management strategies where the timing and methods of application were varied along with the total quantities of N applied. Sensor-based N management was compared with the predominant practice of banding predetermined amounts of N at seeding. On average, sensor-based N management resulted in a 34 kg N ha-1 reduction in fertilizer use with no effect on seed yields except at Indian Head in 2006 where dry conditions resulted in yield reductions of 370 to 454 kg ha-1 compared with applying canola's entire N requirements at seeding. Sensor-based N management or split-N applications never increased yields relative to applying all N at seeding. Adopting this technology in western Canada will more likely result in reduced N inputs without reducing yield than increased seed yield. While sensor-based N management did not reduce post-harvest residual soil NO3-N levels, agronomic N use efficiency (ANUE) was increased 33% of the time and was never lessened. When significant, the increase in ANUE ranged from 4.8 to 7.8 kg seed kg N applied-1. Overall, optical sensors have potential as a tool for managing N fertility more efficiently in canola production. Key words: Brassica napus, normalized difference vegetation index, urea ammonium-nitrate, nitrogen use efficiency, agriculture, precision