|Maas, Steve - TEXAS TECH UNIVERSITY|
Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: January 20, 2004
Publication Date: January 20, 2004
Citation: Wanjura, D.F., Upchurch, D.R., Maas, S. 2004. Spectral reflectance estimates of cotton biomass and yield. National Cotton Council Beltwide Cotton Conference [abstract]. p. 838-851 Interpretive Summary: Timely detailed information of yield determining factors in agricultural fields is needed to optimize crop production inputs. Remotely measured spectral reflectance is one of the primary technologies used to obtain information about crop conditions. Crop reflectance in 16 individual wavelengths was measured with a hand-held radiometer in a cotton irrigation study. Reflectance in the near infrared region at 750 and 880 nm made during the 2002 and 2003 growing seasons were highly correlated with plant water status, leaf area, and final lint yield. Reflectance correlations with final lint yield tended to increase in 2003 as the measurement date approached the time of crop maturity. While the reflectance correlations were statistically significant a higher level of accuracy is needed before direct measurements of crop characteristics can be replaced with spectrally-derived estimates. More accurate spectral estimates may be achieved by increasing the spatial concentration of spectral measurements.
Technical Abstract: Cotton was grown under three irrigation levels in 2002 and four irrigation levels in 2003 using subsurface drip irrigation. Multi-spectral reflectance measurements made periodically in both years were related to biomass, leaf water potential and final lint yield. Reflectance measurements were made with a hand-held CROPSCAN radiometer equipped with sensors that measured radiation in 16 wavelengths. The objective of this study was to determine the level of correlation of multi-spectral reflectance of cotton with leaf water potential, leaf area, and final yield. After an analysis that included the plotting of all bands for all measurement dates in both years high correlation was observed between several bands. Seven uncorrelated bands were selected to correlate with leaf water potential (LWP), leaf area index (LAI), and final lint yield. Among the individual bands wave lengths of 750 nm and 880 nm were highly correlated with LWP, LAI, and lint yield. The highest correlation with LWP and LAI was R2 = 0.80. The highest R2 values for final lint yield were between 0.7 and 0.8, which tended to increase as measurement date approached the time of crop maturity in 2003. Reflectance correlations in band 660 nm with final lint yield reached R2 values between 0.55 and 0.75. The highest NDVI(880,660) values were 0.70 with LWP in 2003, LAI was 0.75 in 2003, and lint yield reached 0.60 and 0.75 in 2002 and 2003, respectively. While reflectance was significantly correlated with each of the canopy factors, higher precision would be needed to replace measurement of the canopy factors with spectrally-based estimates. 1232456789012345678901234567890123456789012345678901234567890123456789012345