Estimating nitrogen concentration with a portable field fluorometer

Eileen Perry1 and Glenn Fitzgerald2,3

1Agriculture Victoria, Department of Economic Development Jobs, Transport and Resources, Cnr. Midland Highway & Taylors Street, Epsom, Vic, 3551, Australia Eileen.Perry@ecodev.vic.gov.au

2Agriculture Victoria, Department of Economic Development Jobs, Transport and Resources, Grains Innovation Park, 110 Natimuk Road, Horsham, Vic 3400, Australia

3 Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, 4 Water Street, Creswick Victoria 3363, Australia

Abstract

Field-portable active light fluorescence sensors have the potential to provide non-destructive estimates of canopy N, particularly for use in field experiments to supplement tissue analysis. In previous results, a handheld portable fluorometer was related to nitrogen concentration of leaves and stems in wheat, with a positive, linear relationship (R2 = 0.69). In this paper we expand on the previous results, using data collected as part of four separate experiments run at the Australian Grains Free Air CO2 Environment (AGFACE) facility during 2014-2016. The data represent a variety of treatment factors including CO2 (elevated and ambient), several wheat varieties, a range of N fertiliser applications, and differences in seasonal water inputs (rainfed and supplemental). Fluorometer readings were made on the fresh intact leaves, stems and heads from biomass cuts at GS65. Results from the pooled data indicated that plant components had different relationships between N concentration and fluorometer measurements. Linear models were fit for green leaves to relate leaf %N to fluorometer NBI_G. Three of the individual experiments resulted in similar fitted slope and intercept parameters to the overall dataset. Likewise, model parameters for measurements on cv Yitpi and Wyalkatchem were similar. R2 values ranged from 0.65 (2014 all treatments) to 0.25 (Wyalkatchem all years). Values for root mean square deviations (RMSD) ranged from 0.28 to 0.42 (%N). The regression models form the basis of a calibration(s) for field measurements. The desired outcome is to establish a robust calibration across cultivars and N levels that would allow measurements made in the field from DC31 through DC65 to estimate canopy N.

Host

The Australian Society of Agronomy is the professional body for agronomists in Australia. It has approximately 500 active members drawn from government, universities, research organisations and the private sector.

Photo Credits

David Marland Photography david_marland@hotmail.com Southern Farming Systems Agriculture Victoria

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