Nitrogen source effects on canola (Brassica napus L.) grown under conservation agriculture in South Africa

Canola (Brassicanapus L.) growth and yield can be enhanced by, amongst others, choosing the correct rate, source, and timing of N fertilizer. Limited research exists on the effects of nitrogen (N) source on canola growth and yield properties when grown under conservation agriculture. This study compared the performance of different N fertilizer sources on canola biomass production, seed yield, and oil content. Field trials were conducted from 2016 to 2019 at five sites in the Western Cape Province of South Africa which is characterized by a Mediterranean climate. Nitrogen fertilizer source had no effect (p > .05) on biomass production or oil content at any site. Sufficient soil water levels and warm daily temperatures led to greater biomass production regardless of nitrogen source. Oil content was determined by the presence of rainfall during the flowering and seed filling stages. The effect of N source on yield varied among sites in accordance with timing of fertilizer application in relation to rainfall. The urea + urease inhibitor N source led to greater (p < .05) yields than the urea N source without the inhibitor at the Darling site, regardless of the soil water conditions. Mean yield values of all seasons and sites indicated that urea + urease inhibitor fertilizer to be the most reliable N source to ensure optimal yields over the long-term.