Multispectral Reflectance of Cotton Related to Plant Growth, Soil Water and Texture, and Site Elevation.

Li, H¹.  R.J. Lascano¹, E.M. Barnes², J. Booker¹, L.T. Wilson³, K.F. Bronson¹, and E. Segarra^1,4

¹Texas A&M University, Texas Agricultural Experiment Station, Lubbock , Texas

²USDA-ARS, Phoenix, AZ³Texas A&M University, Texas Agricultural Experiment Station, Beaumont , Texas

⁴Texas Tech University, Lubbock , Texas

Abstract

Radiometric data can be useful to determine the impact of field heterogeneity, irrigation and fertilizer application on plant water and N use. A 2-year (1998-99) study was conducted on the South Texas High Plains (USA) to investigate cotton (Gossypium hirsutum) spectral and agronomic responses to irrigation and N fertilizer application and to determine the simple and cross correlation among cotton reflectance, plant growth, N uptake, lint yield, site elevation (SE) and soil water and texture. The treatments were irrigation at 50 and 75% of calculated cotton evapotranspiration (ET) and N rates of 0, 90, and 135 kg/ha arranged in an incomplete block of size-2 design. Plant and soil spectral properties were investigated within a wavelength of 447 to 1752 nm. Near-infrared (NIR) reflectance was positively correlated with plant biomass and N uptake. Reflectance in the red and mid-infrared band increased with SE. The mixed-model analysis showed that cotton NIR reflectance, normalized difference vegetative index (NDVI), soil water, N uptake and lint yield were significantly affected by irrigation (P<0.0012). The N treatment had no effect on spectral parameters, and interaction between irrigation and N fertilizer was significant on NIR reflectance (P<0.0027). All spectral and agronomic parameters measured were associated with SE. The red and NIR reflectance and NDVI were cross-correlated with soil water, sand, clay and SE across a distance of 60 to 80 m. Characterization of plant and soil reflectance and their spatial structure can be the basis for variable N application on heterogeneous fields to increase N use efficiency.

Reference:  Li, H.  R.J. Lascano, E.M. Barnes, J. Booker, L.T. Wilson, K. F. Bronson, and E. Segarra.  2001.  Multispectral reflectance of cotton related to plant growth, soil water and texture, and site elevation.  Agron. J. 93: 6, 1327-1337.