Remote sensing (RS) technologies provide a diagnostic tool that can serve as an early warning system, allowing the agricultural community to intervene early on to counter potential problems before they spread widely and negatively impact crop productivity. With the recent advancements in sensor technologies, data management and data analytics, currently, several RS options are available to the agricultural community. However, the agricultural sector is yet to implement RS technologies fully due to knowledge gaps on their sufficiency, appropriateness and techno-economic feasibilities. This study reviewed the literature between 2000 to 2019 that focused on the application of RS technologies in production agriculture, ranging from field preparation, planting, and in-season applications to harvesting, with the objective of contributing to the scientific understanding on the potential for RS technologies to support decision-making within different production stages. We found an increasing trend in the use of RS technologies in agricultural production over the past 20 years, with a sharp increase in applications of unmanned aerial systems (UASs) after 2015. The largest number of scientific papers related to UASs originated from Europe (34%), followed by the United States (20%) and China (11%). Most of the prior RS studies have focused on soil moisture and in-season crop health monitoring, and less in areas such as soil compaction, subsurface drainage, and crop grain quality monitoring. In summary, the literature highlighted that RS technologies can be used to support site-specific management decisions at various stages of crop production, helping to optimize crop production while addressing environmental quality, profitability, and sustainability.

Spray deposition and coverage within soybean canopies remain critical challenges for achieving effective pesticide applications, particularly under windy conditions. This research investigated the influence of wind speed, boom travel direction relative to wind direction, and nozzle type on droplet deposition, coverage uniformity, canopy penetration, and airflow distributions inside soybean canopies under controlled wind-tunnel airflow. Spray deposition, analyzed using a fluorometric tracer, and coverage, quantified with water-sensitive papers, were assessed in R3-stage soybeans in an 18-m wind tunnel using XR (perpendicular spray) and 3D (38° angle) flat fan nozzles under varying air speeds and boom travel directions in the wind tunnel. Potted plants were placed in the wind tunnel to mimic soybeans grown in field conditions. Droplet sizes of the nozzles were measured using a laser imaging particle sizing system. Airflow velocity and turbulence within the soybean canopy were investigated with a 3-D hot-film anemometer system. The results indicated that wind and boom direction were the main influential factors for spray coverage and deposition. The top canopy position, exposed to the highest air-turbulence intensity, received the greatest deposition, whereas the middle and bottom positions, characterized by lower turbulence, exhibited sharp declines in both deposition and coverage regardless of treatment. The 3D nozzle provided greater coverage and deposition than the XR nozzle only under no-wind conditions; however, under wind conditions, equivalent performance was observed from both nozzles. Therefore, it was essential to incorporate wind conditions and canopy structures into consideration when choosing nozzles to maximize spray penetration and achieve efficient and effective spray applications for soybeans.

Although a pulse-width modulation (PWM) technique controls nozzle flow rate with minimal pressure variation, its effects on droplet size distribution and flow regulation when combined with low-drift nozzle designs are still not well documented. Therefore, the objective of this research was to investigate the effects of PWM on droplet size distribution and flow rate of low-drift nozzles used in pesticide application systems. Experiments were conducted under controlled laboratory conditions to evaluate eight flat-fan nozzles with different designs to increase spray droplet sizes. Each nozzle was coupled with a PWM valve, and tested at duty cycles (DUC) from 20% to 100% in 20% increments, and operating pressures of 276 and 414 kPa. Droplet size distribution was determined using a laser diffraction technique, and nozzle flow rate was evaluated to assess the effects of DUC on spray characteristics. PWM operation showed a strong linear relationship between DUC and flow rate (R² ≥ 0.99). In addition, measured flow rates showed good agreement with theoretical values at DUCs ≥ 60%, whereas substantial deviations were observed at lower DUCs. The effects of DUC on droplet size characteristics varied by nozzle design, pressure, and the parameter evaluated. Low DUCs tended to increase droplet size heterogeneity and the proportion of drift-prone droplets (<150 µm), although these effects were dependent on nozzle type and operating pressure and were not observed consistently across all nozzles. Overall, excessively low DUCs may compromise flow accuracy and spray quality in PWM systems.