Tuesday, November 14, 2006 - 9:00 AM

Crop Reflectance as an Indicator of Cotton Growth and Leaf Nitrogen Status.

Jac Varco, Mississippi State Univ, Mississippi State University, PO Box 9555 Plnt Soil Science, Mississippi State, MS 39762 and Robert Earnest, Mississippi State University, "PO Box 9555, Plnt Soil Science", "PO Box 9555, Plnt Soil Science", Mississippi State, MS 39762, United States of America.

Crop reflectance could serve as a surrogate measurement of crop growth and leaf N status when standardized with in-field point measurements. Thus,  field variability in cotton plant height and leaf N could be mapped and used to provide decision support for spatial agrochemical applications. The objectives of this research were to establish relationships between canopy reflectance and leaf N concentrations and plant height using an on-the-go tractor mounted spectrometer.  A field experiment consisting of four fertilizer N rates to establish differences in plant height, leaf N concentrations, and yield was conducted in 2005. Plant height was measured in conjunction with canopy reflectance and leaf N was measured at early square, early flower, peak flower, and early senescence. The Green Normalized Vegetation Index (GNDVI) was used to determine relationships between reflectance and plant height and leaf N. On-the-go sensing of crop reflectance was strongly related to leaf N and plant height following the 3rd week of squaring through early senescence. The GNDVI appears to be a strong indicator of dry matter and total N accumulation.