Project : USDA ARS

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Research Project: Preserving Water Availability and Quality for Agriculture in the Lower Mississippi River Basin

Location: Delta Water Management Research

2021 Annual Report

Objectives
Objective 1: Measure, model, and/or estimate the impact of current and innovative farming practices on water quantity and quality while sustaining crop yields and reducing environmental impacts in irrigated agroecosystems. Sub-objective 1a: Quantify changes in irrigation water use, water quality, and crop water productivity as a result of implementing innovative rice production practices. Sub-objective 1b: Quantify changes in irrigation water use, water quality, and crop water productivity as a result of implementing innovative row-crop production practices. Objective 2: Develop and/or enhance agronomically sound irrigation and drainage management tools, practices, and technologies that protect and/or increase available water resources. Sub-objective-2a: Evaluate alternative sources of irrigation water. Sub-objective-2b: Evaluate practices and technologies for managed recharge of the MRVA aquifer. Objective 3: Improve watershed management in irrigated agroecosystems of the Lower Mississippi River Basin. Sub-objective 3a: Develop an improved understanding of nutrient and sediment transport, transformations and the hydrology in an irrigated landscape.

Approach
To preserve the quantity and quality of irrigation water supplies in the Lower Mississippi River Basin, it is necessary to consider the range of crops, soils, and production systems; the types of irrigation and drainage systems employed; the level of runoff water recycling employed; and the different water sources available. This project will address ways to improve the sustainability of groundwater supplies by investigating alternative irrigation methods for the crops currently produced in the region. Production system evaluations will include on-farm research with active participation by crop producers and crop advisors. Data collected from on-farm evaluations will be used to inform, enhance and validate existing hydrology models. Findings from this research are expected to reduce agricultural reliance on groundwater and improve water resources management, inform decision makers of potential impacts of conservation practices, and arm producers with tools and technologies that conserve water resources while maintaining crop yield.

Progress Report
Objective 1: As part of the Lower Mississippi River Basin Long-Term Agroecosystem Research (LTAR), unit scientists are measuring water use, water quality, greenhouse gas (GHG) emissions, soil moisture, grain quality, and arsenic levels in rice grain at commercial rice fields. While climate change continues to become a threat to crop production and water resources, innovative technologies associated with rice resilience to high temperature and post-harvest assessment of grain are being investigated by ARS scientists using state-of-the-art infrastructure and instrumentation. Continued field validation of these advanced technologies facilitates the development of rice genomes resilient to climate change. Through collaboration with RiceTec, Dale Bumpers National Rice Research Center, and Arkansas State University (ASU), ARS scientists continue to build upon a database of greenhouse gas emissions by management and variety from the mid-south. Research on the automation of rice irrigation continues and is being conducted on 16 farm fields in NE Arkansas. This study compares water savings, yield, economics, and other parameters of fully-automated, partially automated, and fully-manual irrigation management. Irrigation research involving the use of winter cover crops in a furrow irrigated rice-soybean system continues at two farm locations while a soybean-maize system is being investigated at two other farm locations in cooperation with the University of Arkansas (U of A) and Natural Resources Conservation Service (NRCS). With the long-term research efforts in the study of water management in rice, a unit scientist received the 2020 Sustainability Award from USA Rice. ARS scientists were invited to present their findings at the National Conservation Systems Cotton and Rice Production Conference, Western Rice Belt Conference, Cereals & Grains Association: Connecting Rice Science and Production with Global Sustainability, Embrapa-clima temperado unit (Pelotas, Brazil), CottonWorks for Cotton Inc. Sustainability Webinar series: Pathways to Progress Measuring Improvements Towards the 10-year Sustainability Goals, Brazil Rice Growers Association and Nature Conservancy-ADM Agricultural Water Conservation Meeting. ARS scientists were invited to serve on the Technical Advisory Committee of the National Cotton Council, Field to Market, Arkansas Soil Health Alliance, and USA Rice; and a 5-year external research review panel for the National Agricultural Research Institute of Uruguay (INIA). Objective 2: Research in this objective has been expanded by the unit’s invited participation in the Natural Resources Conservation Service’s Arkansas Groundwater Initiative (AGWI). This NRCS-funded initiative is a 10-year effort whose overarching goal is to reduce aquifer decline in critical groundwater areas located in the Grand Prairie and Cache River Critical Groundwater Areas (CGA) of Arkansas. The program involves collaborations between farmers and ARS, NRCS and US Geological Survey (USGS) personnel. DWMRU scientists will measure irrigation use before and after a range of conservation practices are employed which USGS staff will try to correlate with any resulting changes in groundwater levels. These activities complement on-going efforts to inventory agricultural surface water resources and irrigation practices in the Cache River GCA that will be used to create potential scenarios for attaining groundwater use reductions. The unit has shifted managed groundwater recharge efforts to infiltration galleries (IG). Construction on two IG in the Cache River CGA was completed in February 2021 and plans to introduce water to the systems will begin in Fall of 2021 (recharge activities are limited to fall and winter months). Objective 3: Much of the work in this objective is at the farm- and field-scale, which requires collaboration. Collaboration to meet this objective continued with regional producers, organizations and universities (Arkansas State University, University of Arkansas, and North Carolina A&T State University). Data collection at the nine edge-of-field sites and ten in-stream CEAP sites continued. New funding was secured through U of A collaborators to continue research at four sites that were at the end of their six-year edge-of-field contract with Natural Resources Conservation Service, and to begin data collection at two new rice/soybean sites. The rice/soybean EOF sites now are both coupled with eddy covariance towers capable of measuring fluxes of CO2, H2O, and CH4 at the field scale.

Accomplishments
1. Irrigation innovation in the Lower Mississippi River Basin (LMRB). ARS researchers in Jonesboro, Arkansas, were invited to review the state of surface water irrigation in the LMRB. Between 1950 and 2017, there was a 12-fold increase in irrigated area in Arkansas and a doubling in Louisiana. Groundwater provides over 90% of the irrigation water applied to the 4Mha of cropland in the LMRB. A multi-faceted response to resulting groundwater declines in the region include producers, public and private organizations. Irrigation water management innovations are part of the solution and include precision grading, alternate wetting and drying (AWD) rice irrigation, and automation. Researchers found, in a separate study, that AWD showed no significant difference in measured cumulative evapotranspiration (ET) or yield when compared to the typical delayed flooding (DF) practice. Even during drying events, the AWD elicited no change in ET compared to DF, suggesting the AWD treatment did not induce drought stress in the plants. Other research highlighted the potential opportunity of water savings when implementing automation using a wireless sensor network that tracks water depth in rice fields. The automated system tracked water depth well at nearly all sites. However, in a few instances some logistical challenges of installation of the sensors remain. This information is important to land managers, consultants, and state and federal entities interested in water resources management.

2. Non-continuous flooding practice reduced seasonal methane emissions by >50% but increased cumulative nitrous oxide emissions by 3 to 37% relative to conventional continuous flooding practice. Paddy rice has a higher global warming potential (GWP) among the major cereal crops, mainly due to the methane emissions associated with continuous flooding. Nitrous oxide is mainly produced in rice paddies during drained periods. ARS researchers in Jonesboro, Arkasnas, have proven that rice paddy field aeration practices such as alternate wetting and drying (AWD) and furrow irrigation are a viable approach to mitigate methane emissions in direct seeded rice. The AWD practice reduced methane emissions by 41 to 73%. Drying the field for up to 13 days before re-flooding did not affect the grain yield. However, implementation of cover cropping in furrow rice irrigation reduced grain yield by 29%. While methane emissions were reduced by 77 to 95% in furrow irrigation, nitrous oxide emissions increased 25-fold when compared to conventional flooded rice. The decrease in methane emissions was offset by an increase in nitrous oxide emissions, hence there was no benefit in greenhouse gas emissions from the non-flooding practice relative to conventional flooded rice. This information can benefit extension workers, rice breeders, crop consultants, and importantly rice growers on adopting field aeration practice to save water use, protect the yield and trading of carbon emissions. However, further studies on non-flooding practice focusing on water and fertilizer N management to reduce nitrous oxide emissions are needed to increase water and N use efficiencies with minimal or zero impact on producers’ economic returns.

3. High night air temperature research in rice production. The expected changes in surface air temperature by the end of the 21th century are predicted to be in the range of 0.3 to 4.8oC. Significant warming of air temperature may lead to crop yield reductions. ARS researchers in Jonesboro, Arkansas, looked at temperature trend analysis using actual weather station data during the recent 67-year period and showed a significant increase of 1.12oC and 0.53oC in seasonal night air temperature occurred in California and Arkansas, while Louisiana and Texas showed no increase in night air temperature. These results may impact the rice, a high value crop in Arkansas. It has been reported that each 1°C increase in night-time air temperature led to deterioration of crop yields. In a separate study, researchers used 173 rice accessions and a gene mapping study called genemo-wide association, to identify genes that are strongly associated with the grain width trait under high night air temperature. These genes are involved in the grain development of the rice plant that potentially influences yield. These discoveries will advance the breeding of rice varieties tolerant to heat stress and enable breeders to develop resilient rice genomes under changing climate. Also, these results are highly relevant to crop growers, plant breeders and policy makers in developing climate smart crops and farming systems that are resilient to temperature changes that are happening in some US rice regions.

4. Improving soil drainage and crop irrigation gives farmers more cropping options. Owing to the heavy, clay soils in southern Brazil and Uruguay, the traditional crop rotation involves one year of rice followed by three or more years of cattle grazing. However, farmers in these areas seek to include soybeans in their rice rotations to provide greater cropping flexibility and economic returns. ARS researchers in Jonesboro, Arkansas, conducted research to test precision-grading and furrow-irrigation on lowland soils. When precision grading is coupled with the use of raised seedbeds, drainage improvements required for successful soybean production were achieved. Similarly, the periodic drying of flooded rice soil increased irrigation water use efficiency and reduced the arsenic content in rice grain grown on a lowland soil of southern Brazil, reducing potential health risks associated with this naturally occurring substance.

5. Improved understanding on-farm storage reservoir water availability and water quality. Currently groundwater constitutes 90% of irrigation water in the mid-South, a shift toward using more surface water is a key component to sustainable water resources in the region. ARS researchers in Jonesboro, Arkansas, provided validation data that was used to compare to two Landsat inundation datasets to identify on-farm reservoirs (OFR) in the area. It was determined that both datasets could be used effectively to enhance hydrological assessments, especially those in poorly monitored basins with a high concentration of OFRs. In a separate study, researchers characterized water quality of a select number of these systems. They found that the reservoirs demonstrate a vital role in reducing downstream nutrient contribution of excess nutrients measured (nitrate and dissolved inorganic orthophosphate). Protection of the reservoir banks also contributed to the water quality of the system, with a vegetated bank having lower sediment and nutrient concentrations than those protect with concrete rubble. These findings contribute to the knowledge base of water resources management of the region.

6. Remote sensing advances in the mid-South. New opportunities with Synthetic Aperture Radar (SAR) exist with recent and planned launches. SAR offers a valuable means of monitoring the land surface through cloud layers, which are common to the mid-South. ARS researchers in Jonesboro, Arkansas, worked with collaborators using data acquired with the PALSAR-2 mission estimate soil moisture over agricultural fields in the mid-South. Independent ground measurements were used to test decomposition and machine learning algorithms. The level of accuracy for both algorithms merit further development. Researchers also contributed to the development of L-band SAR prototype products aimed at identifying crop type at four sites in the southern United States. Ground truth data was used to verify remotely sensed data with accuracy consistently over 90% for crop type by late growth stages. Researchers also contributed to the advancement of model-based decomposition and machine learning using to map inundation of rice fields using time-series polarimetric L-band SAR products. These findings are of interest to land managers, consultants, and state and federal agencies interested in understanding water resources of the region.

U.S. DEPARTMENT OF AGRICULTURE

Delta Water Management Research: Jonesboro, AR