Abstract

Accurate nitrogen (N) diagnosis early in the growing season across diverse soil, weather, and management conditions is challenging. Strategies using multi-source data are hypothesized to perform significantly better than approaches using crop sensing information alone. The objective of this study was to evaluate, across diverse environments, the potential for integrating genetic (e.g., comparative relative maturity and growing degree units to key developmental growth stages), environmental (e.g., soil and weather), and management (e.g., seeding rate, irrigation, previous crop, and preplant N rate) information with active canopy sensor data for improved corn N nutrition index (NNI) prediction using machine learning methods. Thirteen site-year corn (Zea mays L.) N rate experiments involving eight N treatments conducted in four US Midwest states in 2015 and 2016 were used for this study. A proximal RapidSCAN CS-45 active canopy sensor was used to collect corn canopy reflectance data around the V9 developmental growth stage. The utility of vegetation indices and ancillary data for predicting corn aboveground biomass, plant N concentration, plant N uptake, and NNI was evaluated using singular variable regression and machine learning methods. The results indicated that when the genetic, environmental, and management data were used together with the active canopy sensor data, corn N status indicators could be more reliably predicted either using support vector regression (R2 = 0.74–0.90 for prediction) or random forest regression models (R2 = 0.84–0.93 for prediction), as compared with using the best-performing single vegetation index or using a normalized difference vegetation index (NDVI) and normalized difference red edge (NDRE) together (R2 < 0.30). The N diagnostic accuracy based on the NNI was 87% using the data fusion approach with random forest regression (kappa statistic = 0.75), which was better than the result of a support vector regression model using the same inputs. The NDRE index was consistently ranked as the most important variable for predicting all the four corn N status indicators, followed by the preplant N rate. It is concluded that incorporating genetic, environmental, and management information with canopy sensing data can significantly improve in-season corn N status prediction and diagnosis across diverse soil and weather conditions.

Highlights

  • Proper nitrogen (N) management is critical for optimizing corn (Zea mays L.) yield and quality, farmer’s profitability, and sustainable development [1,2,3,4]

  • Comprehensive data were collected during this project, corn aboveground biomass (AGB) and plant N concentration (PNC) data were only available at the V9 ± 1 developmental growth stage [32] at 13 site-years from four states (Illinois, Iowa, Missouri, and Nebraska) from the 2015 and 2016 growing seasons

  • The results of this study indicated that hybrid information was most important for AGB prediction, with growing degree units to physiological maturity, silk comparative relative maturity, and growing degree units to silk being the second, third, and fourth most important variables, respectively

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Summary

Introduction

Proper nitrogen (N) management is critical for optimizing corn (Zea mays L.) yield and quality, farmer’s profitability, and sustainable development [1,2,3,4]. N management is challenging, due to its dynamic nature. The combination of these factors results in complex interactions driving N dynamics and the spatial and temporal variability in both soil N supply and crop N demand [2,5]. Mismanaging N can significantly impact food security, environmental sustainability, human health, and climate change [1,2,3]. Precision N management aims to match N supply and crop N demand in both space and time and has the potential to improve N use efficiency and reduce negative environmental impacts [2,4]. Technologies that can be used to reliably and efficiently diagnose crop N status over space and time in a timely manner are urgently needed to guide in-season site-specific N management

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