Near-infrared reflectance spectroscopy analysis of phosphorus in sugarcane leaves

Rapid screening for high leaf P concentration may help sugarcane (interspecific hybrids of Saccharum spp.) growers in the Everglades Agricultural Area reduce P in discharge water, an important component of Everglades restoration. The purpose of this study was to evaluate near-infrared reflectance spectroscopy (NIRS) as a potential tool to analyze sugarcane leaf P concentration. Local calibrations for samples with similar spectral characteristics were calculated using modified partial least-squares regression for the following categories: parents, offspring, fertilizer rate, and water table. Additionally, global calibrations were calculated for It groupings of these local categories. Analyses for much of the study found that the most accurate local calibration was that of fertilizer rate, with R-2 = 0.90 and ratio of standard deviation (s) to standard error of cross validation = 2.17. However, further multiplicative scatter correction of spectral data and the elimination of unneeded wavelength segment points by Martens Uncertainty regression with software that became available later in the study resulted in nearly perfect prediction equations, with r(2) = 0.99 and ratio of s to standard error of prediction greater than or equal to 32.0 for the offspring local equation and the parents + fertilizer rate + water table global equation. These results show that researchers not obtaining calibrations at desired levels of accuracy with NIRS should try to eliminate unneeded wavelength segments. Use of NIRS is proposed as a tool to provide rapid, accurate measurements of sugarcane leaf P content for characterizing commercial cultivars and for screening for high-P cultivars in breeding programs.