Abstract
Abstract: The objective of this work was to evaluate the use of plant height as a calibration variable for improving indirect measurements of the leaf area index (LAI). Three experiments were conducted with different crops - corn (Zea mays), soybean (Glycine max), and sugarcane (Saccharum officinarum) -, to compare the performance of the LAI measured indirectly (LAIind) and corrected by the calibration variable with the LAI measured directly (LAIref). Without the proposed correction, the LAIind tended to be overestimated by 20%, on average, compared with the LAIref, for the three crops. After crop height was used to adjust the LAIind, a strong positive relationship was observed between the LAIref and the corrected LAIind (R2 = 0.96); overestimation was reduced to 4% and the root-mean-square error decreased to 0.35 m2 m-2. The variable canopy height is promising for the correction of the LAI of the soybean, corn, and sugarcane crops.
Highlights
Several commercial instruments may be used for the indirect measurement of the leaf area index (LAI), including the Accupar LP-80 Ceptometer (Meter Group, Inc., Pullman, WA, USA), LAI-2200C Plant Canopy Analyzer (LI-COR, Inc., Lincoln, NE, USA), SunScan Canopy Analysis System (Delta-T Devices Ltd, Cambridge, United Kingdom), and Demon (CSIROpedia, Canberra, Australia) (Adeboye et al, 2019)
The LAIind was overestimated by about 20% compared with the LAIref for soybean, corn, and sugarcane (Figure 1), but it expressed well the time variation of the LAI for the three crops (Table 2)
As in the study of Malone et al (2002), the results probably indicate that the estimates of LAIs with defoliation below 2.0 were likely skewed by a greater proportion of pods, stems and petioles, resulting in higher values than those obtained for the directly measured LAI
Summary
Several commercial instruments may be used for the indirect measurement of the LAI, including the Accupar LP-80 Ceptometer (Meter Group, Inc., Pullman, WA, USA), LAI-2200C Plant Canopy Analyzer (LI-COR, Inc., Lincoln, NE, USA), SunScan Canopy Analysis System (Delta-T Devices Ltd, Cambridge, United Kingdom), and Demon (CSIROpedia, Canberra, Australia) (Adeboye et al, 2019). Of these optical instruments, the LAI-2200C Plant Canopy Analyzer and its predecessor, the LAI‐2000, are among the most used worldwide (Kobayashi et al, 2013; LI-COR, Inc., 2015), and their algorithms are based on the approaches proposed by Miller (1986). In the case of the LAI-2000 analyzer, the manufacturer alerts that there may be divergences in LAI estimates when the plants have a large amount of dead and/or senescent material and recommends that calibrations be made using direct LAI determinations to improve the results (Sbrissia & Silva, 2008)
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