Submitted to: Agronomy Abstracts
Publication Type: Abstract only
Publication Acceptance Date: 11/10/2002
Publication Date: 11/11/2002
Citation: Zhao, D., Reddy, K.R., Kakani, G., Read, J.J. 2002. Canopy spectral reflectance to estimate cotton growth and yield [abstract]. Agronomy Abstracts. CD-ROM. Interpretive Summary: None required.
Technical Abstract: Field experiments were conducted in 2001 to investigate relationships between spectral reflectance (280-2500 nm) and growth and yield in cotton (cv. NuCOTN 33B). Biweekly measurements of canopy reflectance (R), plant height, mainstem nodes, dry weight, and leaf area index were made, and seed cotton yield was obtained by mechanical harvest in September. Seed cotton ranged from 2750 to 4310 kg/ha across 56 plots (15 x 8 m) treated with four rates of nitrogen or a plant growth regulator (PIX; mepiquat chloride), or two levels of furrow irrigation. We calculated 14 previously published reflectance ratios that included wavebands in the near infrared to red (NIR/R) range, as well as a normalized difference vegetation index (NDVI)(R935-R661)/(R935+R661). These reflectance indices were used in simple linear regression to determine if reflectance is related to cotton growth and yield parameters. Results indicated plant height and mainstem nodes could be estimated using NIR/R (R750/R550) by either a logarithmic or linear function (R2 = 0.63-0.67***). Leaf area index and biomass could be estimated using the NIR/R ratios of R935/R650, R750/R550, R935/R661, and using NDVI by an exponential function (R2 = 0.56-0.78***). Seed cotton yield was highly correlated with NDVI around the first flower stage (R = 0.82**). A linear model could be used to estimate cotton yield by the NDVI at the first flower stage. Studies are ongoing in 2002.