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

Nondestructive standing crop estimators are important for efficient monitor ing of native and agronomic systems. This study evaluated plot and pasture estimates of standing crop using LAI-2000, visual obstruction, canopy heigh t, and weighted plate measurements. Research was conducted in Lubbock Count y, Texas, in 1999 on areas dominated by Amarillo fine sandy loam (fine-loam y, 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 i mproved 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 th e only purchased instrument ($4800), whereas the visual obstruction ($6), c anopy height ($14), and weighted plate ($14) instruments were constructed f rom 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) indic ated the weighted plate and visual obstruction were the most accurate model s (445 and 446 kg ha(-1)) followed by LAI-2000 and canopy height models (61 3 and 691 kg ha(-1)). Visual obstruction and weighted plate instruments bot h provided fast, inexpensive measurements with acceptable accuracy. We reco mmend visual obstruction for estimating standing crop (SC) in shortgrass pl ains because it is rapid, inexpensive, and accurate.