The use of terrestrial LiDAR to monitor crop growth and account for within-field variability of crop coefficients and water use

Monitoring the spatio-temporal distribution of crop height and biomass is important for crop management in terms of applying irrigation, fertilizers and pesticides. This paper reports the performance of a terrestrial laser scanner (TLS) for measuring crop height and biomass of a bean crop (Phaseolus vulgaris., cv. ‘Contender’); and crop height for barley (Hordeum vulgare., cv. ‘Carfields CKS1′), and pea (Pisum sativum., cv. ‘Massey’) crops, grown under field conditions. In addition, a method is presented that improves spatio-temporal estimates of crop coefficient (Kc) and crop evapotranspiration (ETc) using TLS data combined with NDVI data (“TLVI method”), compared with standard FAO56 model estimates. Evidence is provided to show that the TLVI method gives accurate estimates of crop growth patterns due to spatial variations in soil, microclimate and plant health, providing a valuable tool for precision crop management. The TLS-derived canopy height method showed a significantly high correlation and low biases and errors with the manually measured canopy height (R2 = o.95, RMSE = 5.85 for barley; R2 = 0.93, RMSE = 3.01 for pea; R2 = 0.91, RMSE = 1.82 for bean). The TLS method also showed potential to estimate bean biomass (R2 = 0.70, RMSE = 37.56). In-field sensor measurements of canopy height and NDVI were used to estimate site specific crop factors required for accurate estimation of daily evapotranspiration losses. These estimates showed general agreement with those predicted by standard dual FAO56 crop coefficients, but in addition were able to detect the spatial variability in crop growth and water requirements which were largely controlled by soil differences. Overall, the results showed that the TLS method has the potential to measure crop height surface and that the TLVI method provides estimates of ETc with a high spatio-temporal resolution for different crops. This approach can be considered a very promising tool for site-specific management.