Estimating Cotton Nitrogen Nutrition Status Using Leaf Greenness and Ground Cover Information

Farrah Muharam,Stephen Maas,Kevin Bronson,Tina Delahunty

doi:10.3390/rs70607007

Farrah Muharam, Stephen Maas + Show 2 more

Open Access

https://doi.org/10.3390/rs70607007

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Abstract

Assessing nitrogen (N) status is important from economic and environmental standpoints. To date, many spectral indices to estimate cotton chlorophyll or N content have been purely developed using statistical analysis approach where they are often subject to site-specific problems. This study describes and tests a novel method of utilizing physical characteristics of N-fertilized cotton and combining field spectral measurements made at different spatial scales as an approach to estimate in-season chlorophyll or leaf N content of field-grown cotton. In this study, leaf greenness estimated from spectral measurements made at the individual leaf, canopy and scene levels was combined with percent ground cover to produce three different indices, named TCCLeaf, TCCCanopy, and TCCScene. These indices worked best for estimating leaf N at early flowering, but not for chlorophyll content. Of the three indices, TCCLeaf showed the best ability to estimate leaf N (R2 = 0.89). These results suggest that the use of green and red-edge wavelengths derived at the leaf scale is best for estimating leaf greenness. TCCCanopy had a slightly lower R2 value than TCCLeaf (0.76), suggesting that the utilization of yellow and red-edge wavelengths obtained at the canopy level could be used as an alternative to estimate leaf N in the absence of leaf spectral information. The relationship between TCCScene and leaf N was the lowest (R2 = 0.50), indicating that the estimation of canopy greenness from scene measurements needs improvement. Results from this study confirmed the potential of these indices as efficient methods for estimating in-season leaf N status of cotton.

Highlights

For an indeterminate plant such as cotton, balancing its vegetative and reproductive growth is essential for optimum yield production
To examine if leaf greenness could be used as a proxy for chlorophyll content of cotton, r values describing the strength of the correlation between leaf greenness and chlorophyll meter readings were evaluated (Table 1)
An exception was leaf greenness obtained at Station 2, where it was not significantly correlated with chlorophyll meter readings

Summary

Introduction

For an indeterminate plant such as cotton, balancing its vegetative and reproductive growth is essential for optimum yield production. While deficient N could directly affect boll production and yield [1,2,3,4,5], excess N application could promote excessive vegetative growth [6]. This excessive growth could lead to delayed boll maturity [7] and increased susceptibility to diseases and boll rot [8]. Wiedenfeld et al [12]

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