A HAND-HELD CROP MEASURING DEVICE FOR ESTIMATING HERBAGE BIOMASS AND LAI STATUS IN AN ITALIAN RYEGRASS FIELD

摘要

In practical agricultural managements, timely and accurate assessments of plant biophysical parameters such as herbage biomass (BM) and leaf area index (LAI) are required to develop a management strategy especially throughout a growing season. This study investigated the use of a cloud-free hand-held crop measuring device which measures three wavebands (550, 650, and 880 nm) (EBARA Co. Ltd., Japan) as an assessing tool for estimating BM and LAI in an Italian ryegrass (Lolium multiflorum Lam.) meadow field (1.8 ha). The data were collected at randomly selected 132 plots for BM and 120 plots for LAI with vegetation sampling through 11 times in two cool growing seasons during October 2010 to March 2011 and December 2011 to March 2012. Eight vegetation indices (Vis) such as normalized difference vegetation index (NDVI) and soil adjustment vegetation index (SAVI) were examined to estimate BM and LAI. The relationship between Vis and parameters were examined using linear regression analyses and significant correlation coefficient (R~2) was observed in most Vis. NDVI showed the highest correlation for both BM (R~2 = 0.77) and LAI (R~2 = 0.81). The robustness of the prediction was examined using cross-year validation. NDVI showed the highest performance for BM (R~2 = 0.77) and SAVI (R~2 = 0.70).