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Canopy reflectance informs in‐season malting barley nitrogen management: An ex‐ante classification approach
Author(s) -
Nelsen Taylor S.,
Lundy Mark E.
Publication year - 2020
Publication title -
agronomy journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 131
eISSN - 1435-0645
pISSN - 0002-1962
DOI - 10.1002/agj2.20397
Subject(s) - hordeum vulgare , normalized difference vegetation index , canopy , agronomy , growing season , nitrogen , leaf area index , fertilizer , yield (engineering) , field experiment , reflectivity , context (archaeology) , crop , environmental science , poaceae , mathematics , biology , chemistry , botany , paleontology , materials science , physics , organic chemistry , optics , metallurgy
Malting barley ( Hordeum vulgare ) requires precise nitrogen (N) fertilizer management to achieve a narrow range of grain protein content (∼9–10.5%) while maintaining yields, but practical tools to accomplish this are lacking. This study hypothesized that canopy reflectance (Normalized Difference Vegetation Index (NDVI)) measured at tillering (Feekes 2–3) and expressed as a sufficiency index (SI), can estimate the likelihood of a site‐specific response to in‐season N fertilizer in malting barley. Canopy reflectance was measured from plots at tillering with a GreenSeeker and unmanned aerial vehicle (UAV) borne multispectral cameras in trials across heterogeneous California agroecosystems. Field experiments included a range of N fertilizer application rates (0–168 kg N ha −1 ) and timings (pre‐plant, tillering, or evenly split), and resulted in a range of crop N sufficiency/deficiency. NDVI‐based SI measurements were categorized into one of three quantitative categories (low, medium, and high) without additional experimental context using Gaussian mixture modeling. Despite that 85% of variation in protein yield was due to site‐year, the reflectance‐based categories indicated whether N fertilizer applied in‐season would increase protein yield ( p < .01). Nitrogen application at tillering increased yield and protein for plots in the “low” and “medium” SI categories (45 and 4% for yield and 16 and 12% for protein, respectively) ( p < .05), while “high” SI plots had neither yield ( p = .23) nor protein ( p = .26) increases. Importantly, the broader agronomic conditions of a site primarily determined whether response to in‐season N manifested as increased yield or protein.