Prospects for Monitoring Cotton Crop Maturity with Normalized Difference Vegetation Index

Cotton ( Gossypium hirsutum L.) producers monitor crop maturity during the season to determine when to terminate inputs and to defoliate. COTMAN monitors crop maturity based on time for plants to reach five nodes above white flower (NAWF = 5). Normalized difference vegetation index (NDVI) estimates crop biomass and condition from canopy reflectance of near‐infrared and visible radiation. We conducted a 4‐yr study at Jackson, TN to evaluate the suitability of NDVI for monitoring cotton crop maturity, relative to COTMAN. Maturity was altered by combinations of winter cover crop and N fertilization. Flowering was monitored to determine the date of NAWF = 5 for COTMAN, which predicted later maturity with higher N rates. Relative to zero N, boll opening was delayed by 100 kg N ha −1 in 3 yr. Cover crop effects on NAWF = 5 and maturity were inconsistent. Canopy NDVI data were collected weekly after mid‐bloom with a hand‐held GreenSeeker red/near‐infrared sensor. Significant date × treatment interactions for NDVI indicated the potential to detect maturity differences with NDVI. However, dissimilar time courses of NDVI were obtained in different years, complicating efforts to develop an empirical model of NDVI attenuation with crop maturity. Late‐season NDVI was correlated with degree‐days to open boll in 3 yr, but differences in NDVI corresponding to crop maturity differences occurred later in the season than NAWF = 5 used by COTMAN. Relationships between changes in NDVI and crop maturity did not provide a simple basis for predicting readiness for defoliation similar to COTMAN. Improved multispectral sensors are needed for monitoring row crop condition and maturity.