A wireless device for continuous frond elongation measurement

Growth rate is one of the indicators for a plant's physiological condition. Date palms are characterized by high frond elongation rates, which are mainly subjected to drought and salinity stresses. Thus, continuous measurement of these rates can provide real-time growth information, for assessing water status within the soil-plant-atmosphere continuum of cultivated date palms. This study introduces a novel device, the Palmeter, which continuously measures real-time date palm frond elongation. The Palmeter was calibrated in the laboratory and tested in a date palm orchard with a measurement resolution of 0.52 mm. A field test indicated that the Palmeter could wirelessly transmit acquired data to a signal receiver over a distance of 100 m with a success rate of more than 98%, facilitating the establishment of wireless sensor networks in date palm orchards. Neither temperature nor wind affected the Palmeter measurement within the orchard. The temporal patterns of the frond elongation measured by the Palmeter were found to be sensitive to various cultivation treatments, such as fruit load regimes, applied within a field study. Additionally, a six-volt power supply is recommended in order to reduce the Palmeter's power consumption. The feasibility and robustness of the Palmeter system guaranteed the accurate measurement of the frond elongation under harsh field conditions. Therefore, the Palmeter can be potentially applied to measure the frond elongation of date palms and perhaps other palms, such as oil palms and coconut palms, for irrigation scheduling and cultivation management in large orchards.