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Changes in forage utilization have been difficult to measure non-destructively without some level of subjectivity. This subjec tivity, combined with a lack of reproducibility of visual estimates, has made forage utilization measurement techniques a topic of considerable discussion. The objective of this study was to devel op and test the accuracy and repeatability of an objective, com puter-based technique for measuring changes in plant biomass. Digital photographs of target plants acquired before and after partial defoliation were analyzed using readily available image analysis software. Resulting data were used to develop a simple linear random coefficient model (RC) for estimation of plant bio mass removed based on the area of the plant in the photo. Sample collection took approximately 20 minutes/plant for alfal fa (Medicago sativa L.). Analysis of images took another 60 to 90 minutes. Regression analysis gave an R 2 of 0.969 for predicted vs. observed plant weights. Testing this model using 10 alfalfa plants yielded weight estimates of defoliated plants accurate to within +/‐ 8.5%. The advantage of the RC model is its ability to use easily obtained coefficients from simple linear regression models developed from each plant in a way that accounts for the lack of independence between samples within an individual plant. The technique described here offers an objective and accurate method for measuring changes in plant biomass with possible applications in ecology, botany, and range science. In particular, application of this technique for estimating forage utilization may improve accuracy of estimates and, thereby, improve range management practices.

Studies were conducted in the Sacramento Mountains, New Mexico, to determine the intluence of juniper (Juniperus monosperma [Engelm.] Sarg.) canopy on understory vegetation. The basal area of grass species was estimated at 6 locations beneath the canopies of 50 one-seed junipers. Other parameters measured were litter depth, canopy height, canopy cover, canopy closure, tree height, trunk diameter, north-south crown diameter, and east-west crown diameter. Locations adjacent to the trunk had the greatest juniper canopy cover and litter depths, and the lowest height to canopy. Locations at the end of the canopy had the least crown cover and litter depths, and the greatest height to canopy. All but one of the grass species had greater basal areas at the edge locations and the least at the interior locations beneath juniper canopies. Pinyon ricegrass(Piptochuetiumfimbriatum [H.B.K.] Hitch.) was the exception; it was never found at the exterior locations. Regression models indicated that shading influenced the basal areas of most grass species. Litter depth was negatively correlated with grass basal cover in only 4 models and positively correlated in 1. Basal area of pinyon ricegrass was positively correlated with trunk diameter, a reflection of tree age, indicating that the grass requires time to become established. Also, basal area of pinyon ricegrass was positively correlated with canopy cover, indicating that this species requires the modified microenvironment afforded by shading.

Highlight: Fertilization with 40 lb of nitrogen per acre generally increased crude protein content of blue grama plants during the growing season but not during the dormant season. However, because of increased dry matter yield under fertilization, total protein on the fertilized area exceeded that on the unfertilized area by 37 lb/acre during the dormant season. Fertilization decreased content of ash, silica and acid detergent fiber and had little effect on ether extract, cell wall constituents, acid detergent lignin, carotene content or in vitro dry matter digestibility or content of individual mineral elements of blue grama. Results indicated very little improvement in nutritive quality of blue grama during early spring stress period when cows are lactating and forage quality and quantity are low.