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HighlightsBetween 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 4 Mha of cropland in the LMRB.Ongoing efforts to address aquifer declines have been multi-faceted and include those of producers, public (local, state, and federal) institutions, and private organizations.Irrigation water management innovations include precision grading, reduced-flood or no-flood rice irrigation, pump automation, computerized hole selection, flowmeter requirements, and permit-based water use limitations.Abstract. The Lower Mississippi River Basin (LMRB) is an agricultural region of national and international significance. The basin relies heavily on the Mississippi River Valley alluvial aquifer to provide over 90% of the irrigation water applied to over four million hectares of cropland, with Arkansas using approximately 70% of the water and Mississippi and Missouri using approximately 15% each. Surface methods predominate, especially furrow irrigation using plastic lay-flat tubing in corn, cotton, peanut, and soybean and flood methods in rice. Irrigation extent has steadily increased by approximately 2% per year, such that irrigation withdrawals, combined with the region’s geology, have led to considerable aquifer declines in portions of Arkansas and Mississippi. Attempts to address these declines have been multi-faceted and include innovations in crop management and source water management, and programs in water resources management. Crop management innovations are focused on soybean and rice production and include precision grading, reduced-flood or no-flood rice irrigation, pump automation, and computerized hole selection. Adoption of these practices remains heavily reliant on field demonstrations and extension outreach. Source water management innovations include on-farm reservoirs, managed aquifer recharge, and regional-scale river diversions. Due to the concerted efforts of producers participating in regional and state programs, progress has been made in making surface irrigation more efficient and less reliant on groundwater. However, aquifer decline remains a challenge to the LMRB’s economy, ecology, and culture. Keywords: Aquifer decline, Irrigation, Lower Mississippi River Basin, Mississippi River Valley alluvial aquifer, Surface water.

Research was conducted to help rice (Oryza sativa L.) farmers increase rainfall capture to offset groundwater use in the Lower Mississippi River Valley (LMRV). The LMRV is where a majority ...

(1) Background: Elevated atmospheric CO2 concentration affects the growth and development of the rice crop. In Southern Brazil, rice is traditionally produced with continuous irrigation, implying a significant amount of water used. Besides, continuous flooding favors the uptake of toxic elements such as arsenic (As) and cadmium (Cd). In this work, one Brazilian rice cultivar (IRGA 424) was tested for the effects of elevated CO2 concentration and different water regimes on rice yield, and As and Cd accumulation in grain. (2) Methods: Rice was grown in two CO2 concentrations (400 and 700 µmol mol−1) and two irrigation regimes (continuous and intermittent). It was evaluated the number of tillers, plant height, aboveground dry weight (ADW), water use efficiency (WUE), rice yield components, and As and Cd concentration in rice grain. (3) Results: Rice plants were taller and had a higher WUE when cultivated at e[CO2]. The ADW and the rice yield component were not affected by CO2 levels nor water regimes. Intermittent flood regimes had a lower average As concentration. The Cd concentration in the samples in both growing seasons and all treatments was below the limit of quantitation (8.76 μg kg−1). (4) Conclusions: Enhanced CO2 concentration did not affect rice yield, increased the WUE, and reduced As concentration in grains. Regarding water management, the intermittent regime enhanced WUE and promoted a reduction in As concentration in grains.

Use of furrow irrigation in row crop production is a common practice through much of the Midsouth US and yet, nutrients can be transported off-site through surface runoff. A field study with cotton (Gossypium hirsutum, L.) was conducted to understand the impact of furrow tillage practices and nitrogen (N) fertilizer placement on characteristics of runoff water quality during the growing season. The experiment was designed as a randomized complete block design with conventional (CT) and conservation furrow tillage (FT) in combination with either urea (URN) broadcast or 32% urea ammonium nitrate (UAN) injected, each applied at 101 kg N ha− 1. Concentrations of ammonium (NH4-N), nitrate (NO3-N), nitrite (NO2-N), and dissolved phosphorus (P) in irrigation runoff water and lint yields were measured in all treatments. The intensity and chemical form of nutrient losses were primarily controlled by water runoff volume and agronomic practice. Across tillage and fertilizer N treatments, median N concentrations in the runoff were

Information on the dissipation of clomazone, imazapyr, and imazapic in paddy water under different irrigation system is not available in the literature. The objective of this study was to investigate the effect of two irrigation systems (intermittent (IF) and continuous (CF) flood) on the dissipation of clomazone, imazapyr, and imazapic in paddy water. Imazapic was the least persistent herbicide in paddy water, with DT50-values of approximately 3 and 5d under CF and IF, respectively. Imazapyr required a two-fold increase in time to reach its half-life in water in contrast to imazapic, with DT50-values of approximately 6 and 11d under CF and IF, respectively. Clomazone showed the highest DT50-values, varying between 7 to 21d under CF and IF, respectively. Imazapyr and imazapic dissipation was faster under CF, while clomazone was not affected. This investigation found that the dissipation behaviors of herbicides vary under different rice irrigation regimes. Thus changes in irrigation management, as will be required to produce more rice grain with less water to avoid future scarcity, should consider impacts of flood management on herbicide persistence and environmental behavior.

Inconsistent control of barnyardgrass with bispyribac may be alleviated through adjuvant technology. Experiments were conducted to determine the effect of adjuvant and urea ammonium nitrate (UAN) on absorption and translocation of bispyribac in barnyardgrass. Additional experiments were conducted to determine when maximum absorption and translocation occurred with the use of a methylated seed oil/organosilicone adjuvant (MSO/OSL) plus UAN (0.37 L ha−1and 2% v/v). In the initial experiment,14C-bispyribac–treated leaves, nontreated leaves, and roots were collected 6 and 24 h after application. Absorption was greatest with tank-mixed MSO/OSL (0.37 L ha−1) plus UAN (2% v/v) and the proprietary blend of MSO/OSL/UAN (2% v/v) at 80 and 74% of applied14C-bispyribac, respectively. Translocation to nontreated leaves and roots was also highest with these treatments. Increased translocation appeared to be due to greater herbicide absorption, not an increase in translocation rate. The addition of 32% UAN to MSO/OSL and nonionic organosilicone (OSL/NIS) adjuvant systems resulted in a four to fivefold increase in absorption compared with treatments without UAN. Recovery of14C-bispyribac in additional experiments generally decreased as time after application increased; however, recovery was 86% or greater for all time intervals. By 12 h after application, 68% of applied14C-bispyribac was absorbed. At this time,14C-bispyribac was partitioned within the plant in the following manner: 48% in the treated area, 10% in leaf tissue from treated area to tip of the treated leaf, 1.9% in leaf tissue from treated area to collar region of the treated leaf, 1.6% in remaining leaves from collar of treated leaf upward, 5.3% in remaining leaves from collar of treated leaf downward to soil line, and 0.7% in the roots. These data indicate that maximum absorption was achieved within 12 h with a tank mix of MSO/OSL and UAN or the MSO/OSL/UAN blend.

Discoloration of bermudagrass often results from application of MSMA herbicide used to control southern crabgrass and other weeds. However, when products containing iron sulfate (FeSO4) are tank-mixed with MSMA, this discoloration is reduced. Experiments investigated the effect of tank-mixing organic arsenical herbicides with FeSO4or a chelated iron source (Sprint 330) in terms of southern crabgrass control and injury to bermudagrass. Tank-mixing MSMA with FeSO4reduced bermudagrass injury. However, southern crabgrass control was also reduced by at least 50% with the addition of ≥0.38 kg Fe2+ha−1. Neither antagonism nor safening of bermudagrass was observed when the chelated Fe2+source was used. Applying FeSO4as a separate treatment 1 to 4 d before or after MSMA application did not reduce visual burmudagrass injury 1 wk after treatment. Solution pH and FeSO4concentration controlled the extent of complexation and level of antagonism observed in the field; inorganic Fe2+reacted with MSMA to form a complex having reduced herbicidal activity. Potentiometric and spectrophotometric investigations found that methylarsonate, the parent acid of MSMA and other organic arsenical herbicides, reacts with inorganic Fe2+to form a stable 1:1 Fe2+-methylarsonic acid chelate having two points of metal coordination and a stability constant log10(β) = 2.77 ± 0.04. Tank-mixing MSMA with FeSO4to protect against bermudagrass injury negates the benefit of applying the herbicide for weed control, and therefore is not a recommendable practice for turf managers.