A HAND-HELD CROP MEASURING DEVICE FOR ASSESSING SPATIAL VARIABILITY OF HERBAGE BIOMASS AND LAI IN AN ITALIAN RYEGRASS FIELD

摘要

Understanding spatial and temporal distribution of herbage biomass (BM) and leaf area index (LAI) are important in refining agricultural management practice. This study investigated the use of a hand-held crop measuring device (EBARA Co. Ltd., Japan), which measures three wavebands (550, 650, and 880 nm), for estimating spatial and temporal variation of BM and LAI in an Italian ryegrass (Lolium multiflorum Lam.) meadow (1.8 ha). The field experiments were made at five times in a single growing season during October 2010 to April 2011. Using the device, canopy reflectance data was collected at randomly selected 72 plots with vegetation sampling, and BM and LAI were measured for calibration. For mapping purpose, separate spectral readings at 112 plots were conducted on six permanent lines with every 10 m interval in each time. Regression analysis showed that the normalized difference vegetation index (NDVI) was strongly correlated with BM (R~2 = 0.73) and LAI (R~2 = 0.87). The result of geostatistical analysis using semivariogram model represented that optimal sampling intervals were ranging from 8.3 to 11.1 m about BM and from 5.9 to 11.2 m about LAI over the sampling dates. These results suggested that suitable spatial resolutions should be less than 8 m for BM estimation and 6 m for LAI estimation. For estimation and mapping of BM and LAI in Italian ryegrassa, hand-held crop measuring device may thus be an easy and comparatively cloud-free method.