Evaluation of AccuPAR LP 80 in Estimating Leaf Area Index of Soybeans Canopy in Ile-Ife, Nigeria

Rapid and reliable measurements of leaf area index (LAI) of soybeans are important for modelling biophysical processes, energy and water flux and management of weeds in the plant communities. AccuPAR LP 80 and central leaflet width method were used in computing green LAI (gLAI) of two varieties of row spaced rainfed soybeans: TGX 1448 2E and TGX 1440 1E for two seasons. There were five levels of soil fertility which generated 2 by 5 factorial experiments that were arranged in a randomised complete block design. The gLAI estimated during the initial, development, reproductive and maturity of the crop was compared using regression analysis. The gLAI obtained by the methods was significantly correlated (0.77 ≤ r2 ≤ 0.99, p < 0.0001; standard error of estimate, 0.05 ≤ SEE ≤ 0.67) in the two seasons. Pooled over the seasons and dataset, the two methods were linearly correlated (r2 = 0.89, p < 0.0001; SEE = 0.53). Degree of agreement ranged from 0.96 to 1.00 in the seasons. Regression coefficients ranged from 0.50 to 1.21, while the intercepts were between − 0.15 and 0.78 which indicates deviation from 1:1 line. Mean biased error ranged from − 1.74 to 0.19. AccuPAR LP 80 underestimated LAI from flowering or LAI ≥ 1.11 m2 m−2 and overestimated it during initial and late seasons. Considering the overall performance of the sensor and the rapid measurements, the sensor gave reliable and useful LAI for row spaced rainfed soybeans.