Canopy vegetation indices can predict the spatial variability in grain yield before harvest across large spatial scale. Spring wheat (Triticum aestivum L.) canopy reflectance data using a hand-held active sensor (RapidScan CS-45) and a small unmanned aerial vehicle (sUAV)-based passive light optical sensor (Micasense Red-Edge) were collected three times during flag leaf to heading stages (in the month of June and July) from 16 site-years across the Red River Valley of Minnesota and North Dakota. Potential of vegetation indices (VIs), red normalized vegetation (RNDVI) and red edge normalized vegetation (RENDVI), were compared to predict grain yield and protein content. Linear regression between two sensors showed a significant (p < .05) relationship based on RNDVI (R 2 = .69) and RENDVI (R 2 = .55) values (n = 48). Only for the 2nd year, RENDVI from both sensors could predict the grain yield; but only the RENDVI from sUAV-based passive sensor could predict the protein content at Haun stages between five and eight (R 2 = .60, RMSE = 14.8, p = .02). Use of sUAV based passive sensor has potential to predict protein content but selecting optimal growth stage and validation of developed regression models in neighboring fields are critical for the accurate prediction.Abbreviations: RENDVI, rededge normalized vegetation index; RNDVI, red normalized vegetation index; sUAV, small unmanned aerial vehicle.

Nitrogen dynamics varies spatially in response to complex interactions among weather, soil, and management practices. Twenty-six spring wheat (Triticum aestivum L.) fields were studied for N losses, nitrous oxide (N 2 O) flux and ammonia (NH 3 ) volatilization, grain yield and protein concentration in farmers fields in Minnesota and North Dakota of the Red River Valley during 2018-2020 growing seasons. Spring wheat grain yield ranged from 2.8 to 9.7 Mg ha -1 with protein concentration ranging between 106 and 180 g kg -1 . Average cumulative N 2 O and NH 3 losses were 415 g N 2 O-N ha -1 and 1.43 kg NH 3 ha -1 , respectively (n = 26). Spring wheat grain yield (r = .53, p = .01) had positive association with May rainfall. Grain protein concentration declined with delay in planting (r = -0.55, p = .01). Linear regression indicates a close association of daily N 2 O flux with soil moisture (r 2 = .23, p < .01), soil inorganic N concentration (r 2 = .02, p = .04), and days after planting (r 2 = .20, p < .01). Soil inorganic N concentration (just after planting) had a positive association with cumulative N 2 O flux (r = .41, p = .03). This study showed rainfall, soil moisture, and inorganic N concentration play a dominant role in N dynamics across the region.