Delta Water Management Research Unit

Abstract BackgroundThe development of alfalfa cultivars with improved digestibility may minimize the yield‐quality tradeoff, enabling higher quality with late‐harvested forage and possibly higher yields.MethodsAn irrigated experiment conducted over 4 years compared 28‐d harvest schedules with 35‐d harvest schedules and an alternating 21‐d and 35‐d schedule. Four conventional cultivars and four cultivars developed for higher digestibility were grown under each schedule.ResultsDelayed cutting (35‐d) yields were 16% greater and the staggered treatments were 6% higher than the 28‐d strategy. The nutritive value decreased significantly with the 35‐d schedule, but a “staggered” system provided nutritive value similar to the 28‐d schedule while achieving higher yields. The nutritive value of cultivars was in the order of HarvXtra>Hi‐Gest> conventional cultivars. The HarvXtra but not Hi‐Gest cultivars achieved similar digestibility under the 35‐d cutting schedule compared with conventional cultivars on a 28‐d schedule.ConclusionsThis study clearly demonstrates that higher nutritive value cultivars of fall dormancy 6–9 grown with staggered or late cutting schedules can increase yields while maintaining higher nutritive value. The combination of staggered or late schedules with improved cultivars can maximize yields while maintaining the nutritive value of alfalfa, potentially breaking the alfalfa yield‐quality tradeoff.

Long-term research is essential for guiding the development of agroecosystems to meet escalating production demands in a manner that is environmentally sound and socially acceptable. Research must integrate biophysical and socioeconomic factors to provide geographically scalable knowledge that involves stakeholders across the research-education-extension-policy spectrum. In response to this need, the Long-Term Agroecosystem Research (LTAR) network developed a "Common Experiment," which seeks to develop and disseminate multi-region, science-based information to enable implementation of visionary agricultural innovations while simultaneously promoting food security, well-being, environmental quality, and climate adaptation and mitigation. The core design of the Common Experiment contrasts prevailing and alternative/aspirational production systems, with the latter including novel innovations hypothesized to advance sustainable intensification in locally appropriate ways. Treatments in the Common Experiment represent a diversity of production systems under cropland, grazing land, and integrated crop/grazing land management. Where possible, treatments are evaluated at multiple spatial scales (e.g., from plot to enterprise) and are designed to evolve over the course of the experiment with stakeholder input. A common assessment framework guides data collection for the experiment and is complemented by metric-specific protocols and an emerging data management infrastructure. Currently, there are large differences among sites in the application of the experimental framework and degree of stakeholder engagement; differences largely grounded in pragmatic issues related to land access, site expertise, and resource availability. The full potential of the LTAR Common Experiment may be realized with strategic investments in network capacity.

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.

Rice paddies are one of the major sources of anthropogenic methane (CH4 ) emissions. The alternate wetting and drying (AWD) irrigation management has been shown to reduce CH4 emissions and total global warming potential (GWP) (CH4 and nitrous oxide [N2 O]). However, there is limited information about utilizing AWD management to reduce greenhouse gas (GHG) emissions from commercial-scale continuous rice fields. This study was conducted for five consecutive growing seasons (2015-2019) on a pair of adjacent fields in a commercial farm in Arkansas under long-term continuous rice rotation irrigated with either continuously flooded (CF) or AWD conditions. The cumulative CH4 emissions in the growing season across the two fields and 5 years ranged from 41 to 123kg CH4 -C ha-1 for CF and 1 to 73kg CH4 -C ha-1 for AWD. On average, AWD reduced CH4 emissions by 73% relative to CH4 emissions in CF fields. Compared to N2 O emissions, CH4 emissions dominated the GWP with an average contribution of 91% in both irrigation treatments. There was no significant variation in grain yield (7.3-11.9 Mg ha-1 ) or growing season N2 O emissions (-0.02 to 0.51kg N2 O-N ha-1 ) between the irrigation treatments. The yield-scaled GWP was 368 and 173kg CO2 eq. Mg-1 season-1 for CF and AWD, respectively, showing the feasibility of AWD on a commercial farm to reduce the total GHG emissions while sustaining grain yield. Seasonal variations of GHG emissions observed within fields showed total GHG emissions were predominantly influenced by weather (precipitation) and crop and irrigation management. The influence of air temperature and floodwater heights on GHG emissions had high degree of variability among years and fields. These findings demonstrate that the use of multiyear GHG emission datasets could better capture variability of GHG emissions associated with rice production and could improve field verification of GHG emission models and scaling factors for commercial rice farms.

The specialization and intensification of agriculture have produced incredible gains in productivity, quality, and availability of agricultural commodities but have resulted in the separation of crop and animal production. A by-product of this separation has been the accumulation of manure regions where animal production is concentrated. Enter the "manureshed," an organizing framework for integrating animal and crop production where budgeting of manure nutrients is used to strategically guide their recycling and reuse in agricultural production systems where manure resources are of highest value. To move beyond regional nutrient balance analyses into the transformational realm required to mitigate "wicked" manure problems, manureshed management requires recognition of the challenges to systematically reorganizing resource flows. In better integrating crop and livestock systems, manureshed management must account for the unique nature of managing manure nutrients within individual livestock industries, anticipate trade-offs in substituting manure for commercial fertilizer, promote technologies to refine manure, and engage extensive social networks across scales that range from the farmgate to nation and beyond.

A semi-empirical approach based on surface-renewal theory for estimating the friction velocity is tested for measurements taken in the inertial sublayer. For unstable cases, the input requirements are the mean wind speed and the high-frequency trace (10 or 20 Hz) of the air or sonic temperature. The method has been extended to traces of water vapour (H2O) and carbon dioxide (CO2) concentrations. For stable cases, the stability parameter must also be considered. The method’s performance, taking the direct friction velocity measured by sonic anemometry as a reference, was tested over a growing cotton field that included bare soil with some crop residues at the beginning of the season. In general, the proposed friction-velocity estimates are reliable. For unstable cases, the method shows the potential to outperform the wind logarithmic-law computation. Discarding cases with low wind speeds (e.g., < 0.3 m s−1 and mean wind shear < 1 Hz), the proposed approach may be recommended as an alternative method to estimating the friction velocity. There is the potential, based on the input requirements, that the proposed formulation may offer significant advantages in the estimation of the friction velocity in some marine environments.

HighlightsDeployed a wireless sensor network to track flood irrigation management in ~255 ha production scale rice fieldsUltrasonic sensors were installed in rice fields and water level data were wirelessly transmitted for the growing seasonStudy found significant relationship between automated and manual measurement methodsPotential benefits of using wireless sensor networks are described Abstract. The inclusion of automation in agricultural irrigation may improve crop management by providing organized, site-specific, and real-time information to producers. The objective of this study was to develop a rugged, wireless sensor network (WSN) and infrastructure to retrieve, process, and disseminate sensor data installed in remote rice fields. The study took place during the 2018 rice production season in eastern Arkansas. A working prototype WSN (consisting of 24 sensor nodes) was assembled and field-tested in sixteen production-sized (approximately 16 ha each) irrigated rice fields. Data were collected during the growing season and included water depth and soil water. The WSN retrieved, processed, and disseminated in-situ data from the production fields to a remote computer server. Data were made viewable via a web browser on internet-connected computers and mobile devices. The analysis quantified the benefits, costs, and practical usability of the system to assist with field condition monitoring and irrigation management in production-sized rice farming operations. Water level measurements using the WSN unit were significantly related to the actual measurements in Multiple-inlet rice irrigation (MIRI), Row rice (ROW), and Alternate wetting and drying (AWD) irrigation treatments (r = 0.453 to 0.946, p = &amp;lt;0.0001). However, the reliability of this equipment was challenged by field installation and maintenance. Several in-house troubleshooting methods are discussed to ensure accurate usage of this automated system in future deployments. The results of the study indicated the use of the ultrasonic sensor for estimating water level in MIRI, ROW and AWD irrigation to be a viable solution for future WSN development. The functional WSN supported sensors for automated water level and soil water measurements that could, in future, provide real-time knowledge of the field condition, and enhance resource management for the producer. Keywords: Field condition monitoring, Production scale field monitoring, Remote sensor, Wireless sensor, Wireless sensor network.

Abstract Background and objectivesCurrent global concerns about water scarcity present a need to investigate more water‐efficient rice production methods. Alternate wetting and drying (AWD) is fast emerging as a water‐saving irrigation practice, but its effects on rice quality are largely unknown. To ascertain the impact of water‐saving irrigation practices on rice quality, three irrigation treatments, namely continuous flooding with cascade delivery (four fields); continuous flooding with multiple‐inlet delivery (four fields); and AWD with multiple‐inlet delivery (four fields), were established on 12 production‐sized (16.2 ha) fields in 2017.FindingsResults of rice quality evaluations showed that irrigation treatment had a significant (p &lt; 0.05) effect on chalkiness. Samples harvested from the AWD fields had slightly greater mean chalkiness (5.6%) than samples harvested from the two continuously flooded fields (5.1–5.2%). Milling yields were not affected (p &gt; 0.05) by irrigation treatments. The average milled rice and head rice yields across irrigation treatments were 73% and 59%, respectively. Regarding pasting properties, while peak and breakdown viscosities were not affected (p &gt; 0.05) by the irrigation treatments, setback viscosity (SB), which is often linked with cooked rice texture, was impacted. Among the irrigation treatments, mean SB was least for the AWD treatment (146 cP), while the mean SB for the continuously flooded fields was similar at 168–169 cP.ConclusionsIn summary, the use of AWD with multiple‐inlet delivery did not impact milling yields of rice relative to the conventional practices of continuous flooding. However, rice harvested from the AWD treatment fields had slightly greater chalkiness and lesser SB.Significance and noveltyThis study addresses a gap in literature concerning the impact of emerging water‐saving irrigation techniques, especially AWD as it involves subjecting rice to a certain level of water stress, on rice grain quality characteristics.

Winter cover crops might reduce nutrient loss to leaching in the Upper Midwest. New oilseed-bearing cash cover crops, such as winter camelina ( L.) and pennycress ( L.), may provide needed incentives. However, the abilities of these crops to sequester labile soil nutrients are unknown. To address this unknown, N in shoot biomass, plant-available N and P in soil, and NO-N and soluble reactive P in soil water collected from lysimeters placed at 30, 60, and 100 cm were measured in cover crop and fallow treatments established in spring wheat ( L.) stubble and followed through a cover crop-soybean [ (L.) Merr.] rotation. Five no-till cover treatments (forage radish [ L.], winter rye [ L.], field pennycress, and winter camelina) were compared with two fallow treatments (chisel till and no-till). Pennycress and winter camelina were harvested at maturity after relay sowing of soybean. Winter rye and radish sequestered more N in autumn shoot biomass, ranging from 26 to 38 kg N ha, but overwintering oilseeds matched or exceeded N uptake in spring, ranging 28 to 49 kg N ha before soybean planting. Nitrogen uptake was reflected by reductions in soil water NO-N during cover crop and intercropping phases for all cover treatments (mean = 4 mg L), compared with fallow treatments (mean = 31 mg L). Cash cover crops like pennycress and winter camelina provide both environmental and potential economic resources to growers. They are cash-generating crops able to sequester labile soil nutrients, which protects and promotes soil health from autumn through early summer.