INDIRECT LEAF-AREA INDEX MEASUREMENT AS A TOOL FOR CHARACTERIZING RICE GROWTH AT THE FIELD-SCALE

Indirect methods for determination of crop growth indices may be used as alternatives for measuring growth curves and/or growth variability of field crops. In this study, a commercially available optical sensor was tested for indirect measurement of leaf area index (LAI) of transplanted rice (Oryza sativa L., cv IR-72) under field conditions and compared with destructive crop sampling methods. The instrument was capable of measuring reliable crop growth curves, but may underestimate LAI at higher absolute values (LAI > 4-5). LAI measurements conducted in two 1 above-/4 below-canopy readings at 8 to 10 locations were sufficient to obtain a representative field mean. The sensor may be used to estimate above-ground dry matter yield (DMY) of rice for most of the growing season, but estimates may become erroneous after flowering and at maturity. In addition to destructive plant sampling, quick indirect techniques for characterizing canopy structure may provide information on within-field spatial variability of crop growth.