Spatial characterization of soil mineral nitrogen, crop growth, and yield of canola as affected by nitrogen application

Non-destructive method with the capability of determining the crop N status at early growth stages would be extremely helpful to allow in-season N adjustments according to the soil mineral N (SMN) supply and also to estimate the potential crop yield in its current, specific environment during the growing season of canola (Brassica napus L.). A field experiment was conducted in a cool and humid environment in northern Ontario from 2013-2014, to assess the feasibility of in-season canopy reflectance measurements to characterize soil N supplying power at early growth stage of canola crop and also to estimate potential grain yield of canola, in response to various combinations of preplant (0, 50, 100, 150, 200 kg/ha) and sidedress (50+50, 50+100, 50+150 kg/ha) N applications. Field data were collected throughout the growing period. CropScan was used to get canopy reflectance measurements from pre-sidedressing to early flowering and data were used to compute the normalized difference vegetation index (NDVI). The NDVI values had a strong correlation with SMN levels measured at 20% flowering stage, indicating that canopy reflectance signature is a good indicator of soil N supplying power at early growth stage of canola and could be used for the determination of the required N amounts as sidedress. A strong correlation between NDVI values and canola yields in plots that received different combinations of preplant and sidedressed N indicate that canopy reflectance measurements can be used for estimating potential grain yield of canola. Moreover, split N was more efficiently utilized by canola, leading to greater grain yields than with applying the crop’s entire N requirements at seeding, showing the requirement of in-season N application for canola crop production.