SUGARCANE Near-Infrared Reflectance Spectroscopy Analysis of Phosphorus in Sugarcane Leaves

fore be helpful to develop sugarcane cultivars that produce high yields with less P fertilizer or cultivars that Rapid screening for high leaf P concentration may help sugarcane take up more soil P. Sugarcane in the EAA obtains 30 (interspecific hybrids of Saccharum spp.) growers in the Everglades Agricultural Area reduce P in discharge water, an important compoto 85% of its total P from soil P that was originally in nent of Everglades restoration. The purpose of this study was to the organic form but is mineralized to a plant-available evaluate near-infrared reflectance spectroscopy (NIRS) as a potential form during the sugarcane growth cycle (Anderson, tool to analyze sugarcane leaf P concentration. Local calibrations for 1990). Under well-drained conditions, cultivated Histosamples with similar spectral characteristics were calculated using sols mineralize 6 to 87 kg P ha 1 yr 1 (Diaz et al., 1993). modified partial least-squares regression for the following categories: Phosphorus fertilizer rates are recommended to optiparents, offspring, fertilizer rate, and water table. Additionally, global mize sugarcane yields according to foliar analysis using calibrations were calculated for 11 groupings of these local categories. wet chemistry digestion, coupled with proper interpretaAnalyses for much of the study found that the most accurate local tion of soil testing (Elwali and Gascho, 1984; Anderson, calibration was that of fertilizer rate, with R 2 0.90 and ratio of 1990; Glaz et al., 1997). Using traditional chemical digesstandard deviation (s ) to standard error of cross validation 2.17. However, further multiplicative scatter correction of spectral data and tion and analytical procedures for plant P concentration, the elimination of unneeded wavelength segment points by Martens however, is time consuming and expensive (Malley et Uncertainty regression with software that became available later in al., 2000; Gillon et al., 1999). Perhaps foliar diagnosis the study resulted in nearly perfect prediction equations, with r 2 of leaf P would be more widely used if results were 0.99 and ratio of s to standard error of prediction 32.0 for the more rapidly available so that corrective measures could offspring local equation and the parents fertilizer rate water table be taken before P deficiencies caused yield losses. global equation. These results show that researchers not obtaining Near-infrared reflectance spectroscopy is a rapid anacalibrations at desired levels of accuracy with NIRS should try to lytical method for measuring the chemical composition eliminate unneeded wavelength segments. Use of NIRS is proposed of materials and requires only simple sample preparaas a tool to provide rapid, accurate measurements of sugarcane leaf tion. Covalent bonds between light atoms such as C, N, P content for characterizing commercial cultivars and for screening for high-P cultivars in breeding programs. H, O, and P generally absorb energy in the infrared region where they have fundamental vibrational frequencies and combination overtones detectable in the near-infrared region (400–2500 nm) (Malley et al., 2000; S is the primary crop of the Everglades Gillon et al., 1999). Agricultural Area (EAA) in South Florida, grown Calibration of a near-infrared spectrometer is an inon approximately 134 000 ha of Histosols (Glaz, 2000). ferential process of deriving models that relate spectral Phosphorus deficiency of sugarcane in the EAA may readings of samples to values determined by reference result in reduced cane tonnage, particularly in ratoon chemistry. Calibration involves the selection of reprecrops (Gascho and Kidder, 1979; Glaz et al., 2000). Consentative samples, acquiring spectra and reference analtrarily, excessive P increases cane tonnage, with a correyses, data preparation, and statistical modeling and valilated decrease in sugar concentration, or simply dedation. To minimize interference from the spectra of creases sugar concentration (Gascho and Kidder, 1979; strongly overlapping constituents and from light scatter Glaz and Ulloa, 1994; Glaz et al., 2000). Excessive P variations, spectral data from many different waveapplication also may contribute to P enrichment of surlengths are combined by various methods, including face water (Coale et al., 1994). Most virgin Florida Hismultiple stepwise linear regression, partial least squares, tosols contain from 50 to 1360 mg P kg 1 (Chen and and principal-component analysis (De Boever et al., Ma, 2001), with a majority of the P tied up in organic 1994; Givens and Deaville, 1999). compounds. Differences in P uptake among sugarcane Two broad categories of calibration equations have cultivars could lead to the annual removal of 8.5 kg P been used by researchers: local and global equations. ha 1 from EAA soils (Glaz et al., 1997). It would thereLocal equations are models developed for sample populations expected to have similar spectral characteristics, M. Chen, R.A. Gilbert, and S.H. Daroub, Everglades Res. and Educ. Cent., Univ. of Florida, 3200 E. Palm Beach Rd., Belle Glade, FL whereas global equations are progressively more univer33430; B. Glaz, USDA-ARS Sugarcane Field Stn., 12990 U.S. Highway 441, Canal Point, FL 33438; F.E. Barton II, USDA-ARS Quality Abbreviations: EAA, Everglades Agricultural Area; NIRS, nearAssessment Res., 950 College Station Rd., Athens, GA 30605; and infrared reflectance spectroscopy; RPD, ratio of standard deviation of Y. Wan, South Florida Water Manage. District, 3301 Gun Club Rd., the prediction set to standard error of prediction; s, standard deviation; West Palm Beach, FL 33416. Received 4 Sept. 2001. *Corresponding SEC, standard error of calibration; SECV, standard error of cross author ([email protected]). validation; SEP, standard error of prediction; SNV-D, standard normal variant and detrend. Published in Agron. J. 94:1324–1331 (2002).