Cropland observatory nodes (CRONOS): Proximal, integrated soil-plant-atmosphere monitoring systems

Abstract

Soil-plant-atmosphere conditions in crop fields can differ substantially from those at the nearest weather station, creating uncertainty in crop management decisions and scientific analyses. To reduce this uncertainty, CRopland Observatory NOdeS (CRONOS) were developed to monitor soil water content, green canopy cover (GCC), and atmospheric conditions in crop fields. Here we evaluate the accuracy and reliability of first-generation CRONOS systems and compare CRONOS data to data from the nearest permanent weather station. CRONOS stations were installed in three winter wheat (Triticum aestivum) fields across Oklahoma, USA. Each was equipped with a cosmic-ray neutron sensor to measure soil water content, a camera to monitor GCC, and an all-in-one weather station. Validation sampling showed that CRONOS stations accurately determined field-scale average soil water content, with a mean absolute difference (MAD) of 0.025 cm³cm^-3 and a Nash-Sutcliffe Efficiency (NSE) of 0.742. Greater discrepancies existed between CRONOS GCC estimates and field-scale average GCC, with an MAD of 11% and NSE of 0.67. There was generally strong agreement between CRONOS atmospheric data and data from a collocated, high quality weather station, with NSE values ≥ 0.95 for measurements of air temperature and atmospheric pressure, but slightly poorer agreement for precipitation, solar radiation, relative humidity, and wind speed (NSE values ≥ 0.73). The reliability of the CRONOS cameras needs to be improved because 43% of the scheduled images were missing or unsuitable for GCC analysis, but the reliability of the other sensors was high with ≥ 98% valid observations. Overall, CRONOS stations show good potential to improve monitoring of the soil-plant-atmosphere continuum in cropland.