Craig S. T. Daughtry

Fluorescence sensing systems: In vivo detection of biophysical variations in field corn due to nitrogen supply

Leaf and canopy fluorescence properties of field corn (Zea mays L.) grown under varying levels of nitrogen (N) fertilization were characterized to provide an improved N sensing capability which may assist growers in site-specific N management decisions. In vivo fluorescence emissions can occur in the wavelength region from 300 to 800 nm and are dependent on the wavelength of illumination. These light emissions have been grouped into five primary bands with maxima most frequently received from corn at 320 nm (UV), 450 nm (blue), 530 nm (green), 685 nm (red), and 740 nm (far-red). Two active fluorescence sensing systems have been custom developed; a leaf level Fluorescence Imaging System (FIS), and a canopy level Laser Induced Fluorescence Imaging System (LIFIS). FIS sequentially acquires high-resolution images of fluorescence emission bands under darkened laboratory conditions, while LIFIS simultaneously acquires four band images of plant canopies z 1m 2 under ambient sunlit conditions. Fluorescence emissions induced by these systems along with additional biophysical measures of crop condition; namely, chlorophyll content, N/C ratio, leaf area index (LAI), and grain yield, exhibited similar curvilinear responses to levels of supplied N. A number of significant linear correlations were found among band emissions and several band ratios versus measures of crop condition. Significant differences were obtained for several fluorescence band ratios with respect to the level of supplied N. Leaf adaxial versus abaxial surface emissions exhibited opposing trends with respect to the level of supplied N. Evidence supports that this confounding effect could be removed in part by the green/blue and green/red ratio images. The FIS and LIFIS active fluorescence sensor systems yielded results which support the underlying hypothesis that leaf and canopy fluorescence emissions are associated with other biophysical attributes of crop growth and this information could potentially assist in the site-specific management of variable-rate N fertilization programs.

The current state of precision farming

Abstract Precision farming, or site‐specific farming, has emerged as a promising group of technologies that could increase agricultural productivity with environmental stewardship. It is a knowledge‐based system that integrates many advanced information technologies. Precision farming enables farmers to apply precise amounts of fertilizers, pesticides, water, seeds or other inputs to specific areas where and when they are needed for optimal crop growth. The major components include grid sampling, Global Positioning System (GPS), geographic information systems (GIS), remote sensing, yield monitors, variable rate application (VRA), and computer simulation models. This paper reviews the current state of the art of precision farming and its major components, and discusses economic feasibility and potential implications for agricultural structure and rural communities.

UV band fluorescence (in vivo) and its implications for the remote assessment of nitrogen supply in vegetation

Abstract When excited at 280 nm, intact vegetation produced two overlapping broadband fluorescence emissions; the first centered near 335 nm [ultraviolet` (UV) band], and the second centered near 440 urn (blue band). Separation of these two fluorescence bands was achieved by an iterative nonlinear curve fit procedure utilizing the asymmetric double sigmoidal spectral function. The subsequent ratio of the deconvoluted curve intensities exhibited a significant relation between protein concentration and fluorescence. UV band fluorescence from vegetation treated with varying levels of nitrogen fertilization decreased relative to the blue fluorescence as a function of protein levels. These studies indicate that in vivo UV band fluorescence can be utilized as a nondestructive tool to remotely sense variations in protein concentration due to nitrogen supply. Strong similarities were noted in the UV band fluorescence characteristics of intact vegetation to both membrane-bound and soluble plant proteins containing aromatic amino acids. Pure ribulose 1,5-bisphosphate carboxylase in aqueous solution exhibited UV fluorescence characteristics with excitation and emission distributions similar to those of intact vegetation. Because of its high concentration (up to 70% of the soluble leaf proteins), we believe this protein contributes to the UV band fluorescence emanating from the intact leaf. In addition, similar fluorescence characteristics were observed for two other prominent enzymatic plant proteins; namely, adenosine 5′-tri-phosphatase and carboxylase phosphoenolpyruvate carboxylase. These results indicate that UV band fluorescence emanating from the intact leaf could originate from several plant proteins that contain aromatic amino acids.

Remote sensing of crop parameters with a polarized, frequency-doubled Nd:YAG laser

Polarized laser remote-sensing measurements that correlate the yield, the normalized difference vegetation index, and the leaf area index with the depolarized backscattered radiation from corn plots grown with eight different nitrogen fertilization dosages are presented. A polarized Nd:YAG laser emitting at 1064 and 532 nm is used. Depolarization increased significantly with increasing fertilization at the infrared wavelength, and there was a decrease in the depolarization at the green wavelength. The depolarization spectral difference index, defined as the absolute difference in the depolarization at the two wavelengths, is introduced as a parameter that is an indicator of the condition of the internal leaf structure.

The effects of ambient solar UV radiation on alkaloid production by Erythroxylum novogranatense var. novogranatense.

Truxillines are alkaloids produced by Erythroxylum species and are thought to be derived from the UV‐driven dimerization of cinnamoylcocaines. This study was conducted to determine the effects of ambient UV radiation on the production of truxillines in Erythroxylum novogranatense var. novogranatense. Field plants were grown under shelters covered with plastic filters that were transparent to UV radiation, filtered UV‐B, or both filtered UV‐B and UV‐A radiation. The treatments had no significant effect on plant biomass or specific leaf weight. Absorption values in the UV‐C and UV‐A region of acidified‐methanol leaf extracts were higher for plants exposed to UV radiation compared to the no UV radiation treatment. There was a trend in decreasing levels of trans‐cinnamoylcocaine and a statistically significant decrease in levels of cis‐cinnamoylcocaine in the leaves of plants exposed to UV radiation compared to the no UV radiation treatment. Truxilline levels increased in leaves from plants exposed to UV radiation compared to the no UV radiation treatment. Most significantly, the ratio of truxillines to total cinnamoylcocaines in the leaves was affected by UV, increasing with increased UV exposure. The results support the hypothesis that UV radiation is involved in the formation of truxillines from cinnamoylcocaines.

Deriving chlorophyll fluorescence emissions of vegetation canopies from high resolution field reflectance spectra

Fluorescence of foliage in the laboratory has proven more rigorous than reflectance for correlation to plant physiology. Especially useful are emissions produced from two stable red and far-red chlorophyll fluorescence (ChlF) peaks centered at 685 nm and 735 nm. Methods have been developed elsewhere to extract steady state solar induced fluorescence (SIF) from apparent reflectance of vegetation canopies/landscapes using the Fraunhofer Line Depth (FLD) principal. Our study utilized these methods in conjunction with field-acquired high spectral resolution canopy reflectance spectra obtained in 2004 and 2005 over corn crops and small tree plots of three deciduous species (red maple, tulip poplar, sweet gum). Leaf level measurements were also made of foliage which included ChlF, photosynthesis, and leaf constituents (photosynthetic pigment, carbon (C), and nitrogen (N) contents). As part of ongoing experiments, measurements were made on N application plots within corn (280, 140, 70, and 0 kg N/ha) and tree (0, 37.5, 75, 112.5, 150 kg N /ha) sites at the USDA/Agriculture Research Service in Beltsville, MD. SIF intensities for ChlF were derived directly from canopy reflectance spectra in specific narrow- band regions associated with atmospheric oxygen absorption features centered at 688 and 760 nm. The red/far-red SIF ratio (SIFratio) derived from these field reflectance spectra successfully discriminated foliar pigment ratios altered by N application rates in both corn crops. This ratio was also positively correlated to the C/N ratio at leaf and canopy levels, for the available corn data (e.g., 2004). No consistent N treatment or species differences in SIF were detected in the tree foliage, but additional 2005 data are forthcoming. This study has relevance to future passive satellite remote sensing approaches to monitoring C dynamics from space.

Improving Potential Geographic Distribution Models for Invasive Plants by Remote Sensing

Abstract Remote sensing is used to map the actual distribution of some invasive plant species, such as leafy spurge (Euphorbia esula L.), whereas geospatial models are used to indicate the species potential distribution over a landscape. Geographic data layers were acquired for Crook County, Wyoming, and the potential distribution of leafy spurge presence or absence were predicted with the use of the Weed Invasion Susceptibility Prediction (WISP) model. Hyperspectral imagery and field data were acquired in 1999 over parts of the study area. Leafy spurge presence or absence was classified with the use of the Spectral Angle Mapper with a 74% overall accuracy. However, the user accuracy was 93%, showing that where leafy spurge was indicated in the image, leafy spurge was usually found at that location. With the use of Kappa analysis, there was no agreement between WISP model predictions and either the field data or the classified hyperspectral image. Kappa analysis was then used to compare predictions based on single geographic data layers, to increase the power to detect subtle relationships between independent variables and leafy spurge distribution. The WISP model was revised for leafy spurge based on the remote-sensing analyses, and only a few variables contributed to predictions of leafy spurge distribution. The revised model had significantly increased accuracy, from 52.8% to 61.3% for the field data and from 30.4% to 80.3% for the hyperspectral image classification, primarily by reducing the areas predicted to have potential for invasion. It is generally more cost effective to deal with the initial stages of invasion by only a few plants, compared to an invasion that is large enough to be detected by remote sensing. By reducing the potential area for monitoring, management of invasive plants could be performed more efficiently by field crews.

Effects of O3 and SO2 on leaf characteristics in soybeans grown under ambient- and enriched-carbon dioxide atmosphere

The effects of two air pollutant gases (SO2 and O3) on leaf photosynthesis (PS), leaf chlorophyll (Chl), chlorophyll fluorescence transients (CFTs), leaf reflectance (LR) and canopy reflectance (CR) in soybeans (Glycine max L. Merr.) were studied under both ambient- and elevated-atmospheric (CO2) using open-top chambers. In the CO2 vs. O3 experiment, soybeans Clark were exposed to charcoal filtered air (low-O3) or ambient air + 40 nL L-1(O3) (high O3) during 7 h day-1, 5 days week-1 having (CO2) of 350 (mu) L L-1 CO2 (ambient-CO2) or 500 (mu) L L-1 (enriched-CO2) for 12 h day-1. In the CO2 vs. SO2 experiment, soybeans Essex were exposed to charcoal filtered air (low-SO2) or + 120 nL L-1 SO2 (high-SO2) during 5 hr day-1, 5 days week-1 having the same (CO2) as for the CO2 vs. O3 experiment. Plants were exposed to treatment gases from early growth until maturity. In the CO2 vs. O3 experiment, leaf PS, leaf Chl, and CR showed trends of reduced values under high-O3, while LR was largely unchanged. Leaf PS and CR had increased values under enriched CO2. Leaf Chl and LR were not affected by CO2 enrichment. In the CO2 vs. SO2 experiment, CFTs values indicated that the gases has no impact on the light reactions of photosynthesis. Reduction in leaf PS, leaf Chl, and CR were observed under high-SO2 while LR was unchanged. The enriched CO2 environment increased leaf PS rates but had no effect on LR and leaf Chl.

Remote sensing techniques to monitor nitrogen-driven carbon dynamics in field corn

Patterns of change in vegetation growth and condition are one of the primary indicators of the present and future ecological status of the globe. Nitrogen (N) is involved in photochemical processes and is one of the primary resources regulating plant growth. As a result, biological carbon (C) sequestration is driven by N availability. Large scale monitoring of photosynthetic processes are currently possible only with remote sensing systems that rely heavily on passive reflectance (R) information. Unlike R, fluorescence (F) emitted from chlorophyll is directly related to photochemical reactions and has been extensively used for the elucidation of the photosynthetic pathways. Recent advances in passive fluorescence instrumentation have made the remote acquisition of solar-induced fluorescence possible. The goal of this effort is to evaluate existing reflectance and emerging fluorescence methodologies for determining vegetation parameters related to photosynthetic function and carbon sequestration dynamics in plants. Field corn N treatment levels of 280, 140, 70, and 0 kg N / ha were sampled from an intensive test site for a multi-disciplinary project, Optimizing Production Inputs for Economic and Environmental Enhancement (OPE). Aircraft, near-ground, and leaf-level measurements were used to compare and contrast treatment effects within this experiment site assessed with both reflectance and fluorescence approaches. A number of spectral indices including the R derivative index D730/D705, the normalized difference of R750 vs. R705, and simple ratio R800/R750 differentiated three of the four N fertilization rates and yielded high correlations to three important carbon parameters: C:N, light use efficiency, and grain yield. These results advocate the application of hyperspectral sensors for remotely monitoring carbon cycle dynamics in terrestrial ecosystems.

Fluorescence techniques in agricultural applications

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