Referencing laser and ultrasonic height measurements of barley cultivars by using a herbometre as standard

Assessment of plant height is an important factor for agronomic and breeder decisions; however, current field phenotyping, such as visual scoring or using a ruler, is time consuming, labour intensive, costly and subjective. For agronomists and plant breeders, the most common method used to measure plant height is still a meter stick. In a 3-year study, we have adopted a herbometre similar to a rising plate meter as a reference method to obtain the weighted plant height of barley cultivars and to evaluate vehicle-based ultrasonic and laser distance sensors. Sets of 30 spring barley cultivars and 14 and 60 winter barley cultivars were tested in 2013, 2014 and 2015, respectively. The herbometre was well suited as a reference method allowing for an increased area and was easy to handle. The herbometre measurements within a plot showed very low coefficients of variation. Good and close relationships (R-2 = 0.59, 0.76, 0.80) between the herbometre and the ultrasonic distance sensor measurements were observed in the years 2013, 2014 and 2015, respectively, demonstrating also increased values of heritability. Hence, both sensors were able to differentiate among barley cultivars in standard breeding trials. For the sensors, we observed a 4-fold faster operating time and 6-fold increase of measurement points compared with the herbometre measurement. Based on these results, we conclude that distance sensors represent a powerful and economical high-throughput phenotyping tool for breeders and plant scientists to estimate plant height and to differentiate cultivars for agronomic decisions and breeding activities potentially being also applicable in other small grain cereals with dense crop stands. Particularly, ultrasonic distance sensors may reflect an agronomically and physiologically relevant plant height information.