Comparison of four nondestructive techniques for estimating standing crop in shortgrass plains

Nondestructive standing crop estimators are important for efficient monitoring of native and agronomic systems. This study evaluated plot and pasture estimates of standing crop using LAI-2000, visual obstruction, canopy height, and weighted plate measurements. Research was conducted in Lubbock County, Texas, in 1999 on areas dominated by Amarillo fine sandy loam (fine-loamy, mixed, thermic Aridic Paleustalfs). Five hundred plot estimation samples were collected for each method along 25 transects, and each transect mean was used for the pasture estimation trials. Coefficients of determination improved as we moved from plot (0.34, 0.85, 0.37, and 0.70) to pasture (0.67, 0.87, 0.59, and 0.83) estimation for LAI-2000, visual obstruction, canopy height, and weighted plate measurements, respectively. The LAI-2000 was the only purchased instrument ($4800), whereas the visual obstruction ($6), canopy height ($14), and weighted plate ($14) instruments were constructed from readily available materials. Each instrument provided fast measurements, especially when considering the time required to hand clip the respective measurement areas. Pasture estimation root mean square errors (RMSE) indicated the weighted plate and visual obstruction were the most accurate models (445 and 446 kg ha^-1) followed by LAI-2000 and canopy height models (613 and 691 kg ha^-1). Visual obstruction and weighted plate instruments both provided fast, inexpensive measurements with acceptable accuracy. We recommend visual obstruction for estimating standing crop (SC) in shortgrass plains because it is rapid, inexpensive, and accurate.