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Winter Wheat Crop Reflectance and Nitrogen Sufficiency Index Values are Influenced by Nitrogen and Water Stress
Author(s) -
Clay David E.,
Kharel Tulsi Prasad,
Reese Cheryl,
Beck Dwayne,
Carlson C. Gregg,
Clay Sharon A.,
Reicks Graig
Publication year - 2012
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 - 10.2134/agronj2012.0216
Subject(s) - normalized difference vegetation index , nitrogen , fertilizer , agronomy , crop , yield (engineering) , mathematics , water stress , reflectivity , leaf area index , horticulture , chemistry , biology , materials science , physics , organic chemistry , optics , metallurgy
In‐season N applications to winter wheat ( Triticum aestivum L.) may increase profits and improve N fertilizer accuracy. The objectives of this experiment were to determine the impact of N and water stress on crop reflectance and N sufficiency index (SI) values. The experiment contained five N rates, two water treatments, and four blocks. Crop reflectance was measured at the stem extension and flag leaf growth stages, sufficiency index (SI)‐NDVIw f was ratio between the underfertilized normalized difference vegetation index value {NDVI = [near infrared (NIR)‐red]/[NIR+red]} and the NDVI value from well fertilized and well watered treatments, while SI‐NDVI mz was ratio between underfertilized NDVI values and NDVI values from well fertilized plots within a water stress treatment. Yield losses due to water and N stress were determined using 13 C isotopic discrimination. This research shows that: (i) at the stem extension and flag leaf growth stages, water stress and N stress increased, green, red, and red‐edge reflectance and reduced NDVI values (ii) following the economic optimum nitrogen rate (EONR) produced grain with greater than 120 g kg −1 protein and <10 min stability; (iii) at stem elongation and flag leaf, N fertilizer induced yield gains had a stronger relationship with SI‐NDVI mz (stem extension, r = 0.49*; flag leaf, r = 0.51**) than SI‐NDVI wf (stem extension, r = 0.29; flag leaf, r = 0.33); and (iv) SI‐NDVI mz had greater fertilizer recommendation accuracy than SI‐NDVI wf . These findings suggest that in wheat production, SI should be referenced to well fertilized areas within a management zone.

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