Allometric Method to Estimate Leaf Area Index for Row Crops

Abstract

Core Ideas A new allometric method was developed to estimate LAI for row crops. Good agreement resulted for four crops over multiple seasons. Best agreement resulted using GDD, plant population, and canopy height. Leaf area index (LAI) is critical for predicting plant metabolism, biomass production, evapotranspiration, and greenhouse gas sequestration, but direct LAI measurements are difficult and labor intensive. Several methods are available to measure LAI indirectly or calculate LAI using allometric methods (i.e., exploiting relationships between LAI and more easily measured plant variables), but these depend on other measurements not widely available, and have limited transferability to different seasons. A new allometric method using a log normal function was developed to calculate LAI. Input variables were normalized cumulative growing degree days (CGDD), canopy height (CH), and plant population (PP), which were usually more widely available in crop production datasets. Destructive LAI measurements were obtained over multiple growing seasons for corn (Zea mays L.), cotton (Gossypium hirsutum L.), sorghum (Sorghum bicolor L.), and soybean [Glycine max (L.) Merr.] at USDA‐ARS, Bushland, TX. Log normal functions were calibrated to LAI measurements from a single season of each crop, and tested using independent LAI measurements from all remaining crop seasons. For all crops, discrepancies between calculated and measured LAI resulted in coefficients of determination from 0.23 to 0.85, model indices of agreement from 0.52 to 0.84, root mean square errors from 0.76 to 1.4, mean absolute errors from 0.57 to 1.2, and mean bias errors from ‐0.46 to 0.60. The new allometric method can mitigate missing or sparse LAI data, which will enhance the value of large ecological datasets.

Crop evapotranspiration calculation using infrared thermometers aboard center pivots

“…5). Overall, discrepancies were very similar to a previous study for cotton and grain sorghum, where the allometric model used to calculate LAI was developed and tested (Colaizzi et al, 2017). In the previous study, LAI measurements were also obtained at Bushland, Texas, but for crops planted in straight rows and usually irrigated by lateral move sprinklers.…”

“…However, only canopy width (w C ), canopy height (h C ), and plant population measurements were available in the present study, and LAI measurements were available only in a few seasons and in a limited number of plots. Therefore, LAI was estimated by an allometric method that used plant population, h C , and cumulative growing degree days (Colaizzi et al, 2017).…”

“…Calibration of the meter was checked with a 0.005 m 2 reference disk. Measured LAI was compared to calculated LAI using an allometric method based on h C , plant population, and CGDD (Colaizzi et al, 2017). Because LAI measurements were not available for most of the crop seasons used in the present study, the allometric method was required to calculate LAI for plots used to test the TSEB model.…”

An Overview of Global Leaf Area Index (LAI): Methods, Products, Validation, and Applications

“… where a and b are regression coefficients derived from field measured LAI and DBH for different species, height, and management practices. In many studies, LAI is estimated as a product of the leaf length and width for different plant types and ages (Baret et al, ; Colaizzi et al, ; Homem Antunes et al, ).…”

“…As an alternative, Turner et al () suggested estimating LAI from the sapwood cross‐sectional area, because of their strong physiological relationship. Climatic variables, such as growing degree days and air temperature, have also been added to improve the model performance (Colaizzi et al, ; Yoshida et al, ). Although the approach is more commonly used for forests (Law et al, ; Vyas, et al, ), it has also been explored for crops (Colaizzi et al, ; Yoshida et al, ).…”