Soil mineral nitrogen supply and grain yield estimation of canola in relation to growing-season canopy reflectance measurements

Understanding spatial variability of soil mineral nitrogen (SMN) and crop growth patterns is important for implementing precision nitrogen (N) management strategies for canola. A field experiment was conducted from 2012-2014 in northern Ontario to investigate within field spatial variability of SMN in relation to in-season soil and crop growth measurements and yield map data. A commercial canola field was divided into 12 large strips and each of four rates of preplant N (0, 50, 100 and 150 kg/ha) was implemented. Data were collected throughout the growing season and yields were recorded using yield monitors. Data in 2012 was reported here addressing some key findings. SMN (0-30cm depth) varied significantly across the field-strips and within the field-strips that received the same treatment, indicating the significance of spatial variability in crop N availability at field level. Some crop parameters (LAI, biomass, branches, pods and plants numbers) varied widely across the field with high coefficient of variation, and varied even within the field-strips that received the same treatment. Some crop parameters (plant height, branch numbers) and plant N contents had strong correlations with SMN measured at early flowering, suggesting good potential for in-season site-specific N management for canola. Yield varied significantly (1.7-2.6 t/ha) across the field and among field-strips that received the same treatment. Although yield responded positively to N, yield did not increase consistently with N rates. Compared to the control, only 100N had significantly higher yield, while 50N and 150N had insignificant increases, indicating fertilizer N was not utilized efficiently by canola crop due to the influence of large spatial variability within field. The strong association between spatial variability in SMN and crop measurements and yield provide substantial evidence for site-specific N recommendation for canola based on SMN variability.