RESIDUE EFFECTS ON RADIOMETRIC REFLECTANCE MEASUREMENTS OF NORTHERN GREAT-PLAINS RANGELANDS

The diversity of rangeland ecosystems makes application of remote sensing data difficult. This study was conducted to determine the effects of plant surface residue on rangeland canopy radiometric measurements. Measurements were made on moderately and heavily grazed native rangeland pastures. Standing senesced plant residue was collected and spread in the autumn to establish treatments of 0%, 33%, 66%, and 100% ground cover. Canopy radiometric measurements were made weekly the following grazing season using the red (RED) (0.63-0.69 mu m) and near infrared (NIR) (0.76-0.90 mu m) wavebands of a Mark II radiometer. We examined relationships between wavebands, ratio vegetation index (R = NIR / RED), the normalized difference vegetation index [ND = (NIR - RED) / (NIR + RED)] and forage dry matter accumulation and surface plant residue. All wavebands and indices were significantly related to dry matter accumulation on both moderately and heavily grazed pastures. Separation of residue treatments by radiometric measurements was more evident on moderately grazed than on heavily grazed pastures. Red reflectance was most sensitive to surface residue treatments and separated residue from no residue plots until early June when green growth became dominant. Vegetation indices R and ND tended to be lower for the 100% surface residue treatment for both pastures and higher for the 0% treatment for the moderately grazed pasture. Results suggest that different amounts of surface residue would not greatly interfere with using radiometric measurements to predict dry matter accumulation on Northern Great Plains native rangeland.