Digital Image Analysis of Old World Bluestem Canopy Cover and Leaf Area.

WW-B.Dahl old world bluestem [Bothriochla bladhii (Retz) Blake] is a well-adapted perennial forage grass in the semi-arid Texas High Plains. B.Dahl yields well with limited irrigation where Ogallala Aquifer levels are diminishing. The research aims to estimate leaf area index, percentage light interception, and ground cover from digital image analysis (DIA). Successful application of DIA will aid in refining a simulation model that predicts growth and water use of B.Dahl under limited irrigation conditions. This research used an established pasture of B.Dahl at the Texas Tech University research station at New Deal. Samples were taken biweekly from 12 randomly selected plots during two growing periods: Period 1 was May 22 to July 16, and Period 2 was July 31 to October 16. Field samplings included irradiance, measured above and below canopy for calculating light interception, and overhead photos, taken before clipping biomass at 8 cm stubble height for biomass and leaf area determination. Overhead photos were converted by ImageJ^® software into two color groupings corresponding to green tissue cover and non-green (dead) cover plus bare ground for ground cover simulation. Growth rate was greater in Period 1. Light interception was linearly related to green ground cover as determined from DIA with greater R² value in Period 1. Leaf area index was curvilinearly related to green ground cover in both periods. Grass growth in Period 1 consisted almost exclusively of leaves. Stem elongation and seedhead development introduced high variation in light interception and biomass yield in the latter part of the Period 2. Future study is needed to improve the relationship with DIA and green ground cover, and to evaluate its use under grazing.