Post-processed data and graphical tools for a CONUS-wide eddy flux evapotranspiration dataset.

Large sample datasets of in situ evapotranspiration (ET) measurements with well documented data provenance and quality assurance are critical for water management and many fields of earth science research. We present a post-processed ET oriented dataset at daily and monthly timesteps, from 161 stations, including 148 eddy covariance flux towers, that were chosen based on their data quality from nearly 350 stations across the contiguous United States. In addition to ET, the data includes energy and heat fluxes, meteorological measurements, and reference ET downloaded from gridMET for each flux station. Data processing techniques were conducted in a reproducible manner using open-source software. Most data initially came from the public AmeriFlux network, however, several different networks (e.g., the USDA-Agricultural Research Service) and university partners provided data that was not yet public. Initial half-hourly energy balance data were gap-filled and aggregated to daily frequency, and turbulent fluxes were corrected for energy balance closure error using the FLUXNET2015/ONEFlux energy balance ratio approach. Metadata, diagnostics of energy balance, and interactive graphs of time series data are included for each station. Although the dataset was developed primarily to benchmark satellite-based remote sensing ET models of the OpenET initiative, there are many other potential uses, such as validation for a range of regional hydrologic and atmospheric models.

Inter-annual variability of land surface fluxes across vineyards: the role of climate, phenology, and irrigation management.

Irrigation and other agricultural management practices play a key role in land surface fluxes and their interactions with atmospheric processes. California's Central Valley agricultural productivity is strongly linked to water availability associated with conveyance infrastructure and groundwater, but greater scrutiny over agricultural water use requires better practices particularly during extended and severe drought conditions. The future of irrigated agriculture in California is expected to be characterized neither by perpetual scarcity nor by widespread abundance. Thus, further advancing irrigation technologies and improving management practices will be key for California's agriculture sustainability. In this study, we present micrometeorological observations from the Grape Remote Sensing Atmospheric Profile and Evapotranspiration eXperiment (GRAPEX) project. Daily, seasonal, and inter-seasonal surface flux patterns and relationships across five vineyards over three distinct California wine production regions were investigated. Vineyard actual evapotranspiration showed significant differences at the sub-daily and daily scale when comparisons across wine production regions and varieties were performed. Water use in vineyards in the Central Valley was about 70% greater in comparison to the vineyards at the North Coast area due to canopy size, atmospheric demand, and irrigation inputs. Inter-annual variability of surface fluxes was also significant, even though, overall weather conditions (i.e., air temperature, vapor pressure deficit, wind speed, and solar radiation) were not significantly different. Thus, not only irrigation but also other management practices played a key role in seasonal water use, and given these differences, we conclude that further advancing ground-based techniques to quantify crop water use at an operational scale will be key to facing California's agriculture present and future water challenges. Supplementary Information: The online version contains supplementary material available at 10.1007/s00271-022-00784-0.

Increasing nitrogen use efficiency of corn in midwestern cropping systems.

Nitrogen (N) loss from agricultural systems raises concerns about the potential impact of farming practices on environmental quality. N is a critical input to agricultural production. However, there is little understanding of the interactions among crop water use, N application rates, and soil types. This study was designed to quantify these interactions in corn ( Zea mays L.) grown in production-size fields in central Iowa on the Clarion-Nicollet-Webster soil association. Seasonal water use varied by soil type and N application rate. Yield varied with N application rate, with the highest average yield obtained at 100 kg ha(-1). N use efficiency (NUE) decreased with increasing N application rates, having values around 50%. Water use efficiency (WUE) decreased as N fertilizer rates increased. Analysis of plant growth patterns showed that in the low organic matter soils (lower water-holding capacities), potential yield was not achieved because of water deficits during the grain-filling period. Using precipitation data coupled with daily water use throughout the season, lower organic matter soils showed these soils began to drain earlier in the spring and continued to drain more water throughout the season. The low NUE in these soils together with increased drainage lead to greater N loss from these soils. Improved management decisions have shown that it is possible to couple water use patterns with N application to increase both WUE and NUE.

Preliminary Tests of a Laboratory Chamber Technique Intended to Simulate Pesticide Volatility in the Field.

Pesticides volatilize into the atmosphere in measurable quantities and concentrations; however, reliable methods of trapping pesticide vapors are not readily available. Laboratory simulations of field pesticide volatilization can provide information from which inferences can be made regarding actual field-scale volatilization. The objective of this study was to evaluate a simple laboratory technique that can be used to simulate field volatilization of pesticide vapor, in this particular case metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] vapor. In addition, this study was also used to evaluate the trapping efficiency of XAD-8 sorbent resin for metolachlor. A custom-designed volatilization chamber consisting of a 1.5-L bell-shaped jar was fitted with a vacuum air check valve. The chamber was connected to an air sampling tube that was filled with a polymeric resin, XAD-8, to trap metolachlor vapor. The air sampling tube was connected to a computerized air sampling pump, which could be programmed to sample air from the chamber at a variety of different flow rates and sampling intervals. The volatilization chamber was used inside of a controlled environment chamber to measure metolachlor volatilization from a glass surface over a 24-h period. Total metolachlor recovery averaged 102%. Total metolachlor volatilized under the controlled conditions of this study averaged 84%. Metolachlor trapped by the XAD-8 sorbent averaged 65%. The chamber design performed satisfactorily and when used inside a controlled-environment chamber provides a means of evaluating the effects of various microclimate parameters that influence pesticide volatilization.