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Title: MULTISPECTRAL REFLECTANCE CHARACTERISTICS OF COTTON RELATED TO SOIL WATER, TEXTURE, AND TOPOGRAPHY.

Author
item LI, H - TEXAS A&M UNIV
item LASCANO, R - TEXAS A&M UNIV
item BARNES, EDWARD
item BOOKER, J - TEXAS A&M UNIV
item WILSON, L - TEXAS A&M UNIV
item BRONSON, K - TEXAS A&M UNIV
item SEGARRA, E - TEXAS TECH UNIV

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2001
Publication Date: N/A
Citation: N/A

Interpretive Summary: Many agricultural producers are adopting a new management practice called precision farming where crop needs are determined at a very fine spatial resolution (sometimes as fine as every three to four feet). Determining crop needs at this scale can be very difficult using traditional approaches such as soil or plant samples. In this study it was determined that remotely-sensed measurements of cotton could be related to plant size. This relationship was then used to demonstrate that plant size was affected by field elevation, irrigation treatments, and soil characteristics. Therefore, an agricultural producer could use an image of his field to determine where the crop is growing at different rates and then take samples at only those locations to determine why the differences exist. This has the potential to significantly decrease the number of samples farmers or agricultural consultants need to collect in order to practice precision farming, saving them both time and money.

Technical Abstract: Variability in plant and soil reflectance and crop yield may be attributed to impact of topography and soil texture on water and fertilizer N use. A two-year (1998-1999) multispectral remote sensing study was conducted in a center pivot-irrigated field on the semiarid South Texas High Plains to investigate cotton (Gossypium hirsutum L.) spectral and agronomic response to irrigation and N fertilization and to determine cotton reflectance characteristics, water and N uptake, and lint yield related to topography and soil texture. The treatments consisted of irrigation at 50% and 75% calculated cotton potential evapotranspiration (ET) and N application at rates of 0, 90 and 135 kg ha-1 arranged in an incomplete block design. The multispectral plant and soil reflectance properties were investigated for a wavelength range of 447-1752 nm. Near infrared (NIR) reflectance increased with increasing N uptake and plant biomass. Reflectance in the visible red and mid- infrared bands increased with site elevation and clay content. The mixed model analysis showed that cotton NIR reflectance, normalized difference vegetation index (NDVI), soil and plant water content, N uptake, and lint yield were significantly affected by irrigation (P >0.0012-0.0421). The N treatment had no effect on plant reflectance. Each year, interaction between irrigation and N fertilizer was significant to NIR reflectance (P > 0.0027-0.0152). All measured spectral and agronomic parameters were strongly associated with site elevation and sand content. NIR and red reflectance and NDVI were cross-correlated with soil water, sand, clay, and elevation across a lag distance of ñ 30-40 m. Characterization of spectral plant and soil properties and their