Evaluation of pasture biomass from cool-season pastures in the Midwestern USA with satellite imagery, compared to an electronic plate meter and herbage clippings.

Abstract

Evaluation of pasture biomass measurements aids producers in knowing the availability of cool season grass in pasture for cattle grazing. The objective of this study was to compare satellite technology with the rising plate meter and forage biomass clippings as a method of pasture monitoring in the Upper Midwest of the USA. The study was conducted at the University of Minnesota West Central Research and Outreach Center, Morris, MN grazing dairy from May 2021 to October 2021 and May 2022 to September 2022. The pasture system was composed of cool-season perennials and included mixtures of meadow bromegrass (Bromus riparius Rehmann), meadow fescue (Schedonorus pratensis (Huds.) P. Beauv.), orchardgrass (Dactylis glomerata L.), alfalfa (Medicago sativa L.), red clover (Trifolium pratense L.), and white clover (T. repens L.), and intermediate wheatgrass (Thinopyrum intermedium). Grazing height and forage availability were measured weekly in 9 pastures with a Jenquip pasture plate meter (Jenquip, Feilding, New Zealand). Pastures ranged in size from 2.55 ha to 9.7 ha. Satellite images were from Planet Labs PBC (San Francisco, CA) and average normalized difference vegetation index (NDVI) values were calculated weekly for the area inside each pasture. Pearson correlations were from PROC CORR of SAS 9.4 and determined associations of forage biomass from the plate meter and satellite imagery. Across the summer grazing season, mean forage biomass was 3,267 kg DM/ha (range was 2,864 to 3,622 kg DM/ha) from the plate meter and 2,325 kg DM/ha (range was 985 to 3,321 kg DM/ha) from NDVI satellite images. The correlations for specific pastures of the rising plate meter and the satellite image NDVI ranged from 0.074 to 0.91 and the average correlation was 0.58. Correlations were greater with greater forage availability in the pastures. Alternative methods to calculate the biomass of pastures may provide more advantages for farmers to determine the grazing management of pastures.