The conventional practice of applying nitrogen (N) without adequate information regarding the amount and timing of crop N requirements can result in excessive N fertilizer use, leading to increased greenhouse gas emissions and groundwater contamination. The objective of this research was to improve N management by monitoring plant N status in order to apply N fertilizers at optimal amounts based on site and crop-specific N requirements.

A split-plot design experiment with two winter wheat cultivars (Main plots) and three spring application N rates [Split plots – 0, 100 (recommended rate) and 150 kg/ha] was conducted at the Harrow R&D Centre of Agriculture & Agri-Food Canada in 2021-2022 and 2022-2023. Agronomic, spectrometric, and photosynthetic data were collected at up to three wheat growth stages, and soil and plant N contents were determined at two growth stages. In 2022, 25R34 had significantly lower protein content and test weight, earlier heading, higher seed mass, plant height, and winter survival compared to Pro81. In 2023, 25R34 had significantly lower test weight, earlier heading, higher grain yield and seed mass compared to Pro81.

Lodging was only observed in 2022, and 25R34 showed significantly higher lodging compared to Pro81 particularly at the 100 and 150 kg/ha N rates. In both years, protein content and plant height significantly increased with higher applied N. However, the effect of nitrogen treatments varied between years for several traits suggesting they were influenced by factor(s) other than N fertilizer. At harvest in 2022, Pro81 had significantly higher grain carbon (C) and N contents than 25R34.

Tests of φPSII, which measures the proportion of light utilized by Photosystem II once the leaf is already exposed to light, showed that 25R34 reached a plateau at ~90 kg/ha N; whereas, Pro81 was able to use a higher amounts of light energy in PSII even at the 150 kg/ha N suggesting that Pro81 has a higher capacity for nitrogen use than 25R34.

Further data analysis will investigate associations between soil and plant N contents and hyperspectral data. Hyperspectral sensors may provide a method to monitor in-season plant N status which is integral to implementing precision agriculture because, in addition to crop fertility status, hyperspectral data can provide early indication of plant nutrient and water stresses that may impact yield potential.