Merle M. Anders

Reducing greenhouse gas emissions, water use and grain arsenic levels in rice systems

Agriculture is faced with the challenge of providing healthy food for a growing population at minimal environmental cost. Rice (Oryza sativa), the staple crop for the largest number of people on earth, is grown under flooded soil conditions and uses more water and has higher greenhouse gas (GHG) emissions than most crops. The objective of this study was to test the hypothesis that alternate wetting and drying (AWD--flooding the soil and then allowing to dry down before being reflooded) water management practices will maintain grain yields and concurrently reduce water use, greenhouse gas emissions and arsenic (As) levels in rice. Various treatments ranging in frequency and duration of AWD practices were evaluated at three locations over 2 years. Relative to the flooded control treatment and depending on the AWD treatment, yields were reduced by <1-13%; water-use efficiency was improved by 18-63%, global warming potential (GWP of CH4 and N2 O emissions) reduced by 45-90%, and grain As concentrations reduced by up to 64%. In general, as the severity of AWD increased by allowing the soil to dry out more between flood events, yields declined while the other benefits increased. The reduction in GWP was mostly attributed to a reduction in CH4 emissions as changes in N2 O emissions were minimal among treatments. When AWD was practiced early in the growing season followed by flooding for remainder of season, similar yields as the flooded control were obtained but reduced water use (18%), GWP (45%) and yield-scaled GWP (45%); although grain As concentrations were similar or higher. This highlights that multiple environmental benefits can be realized without sacrificing yield but there may be trade-offs to consider. Importantly, adoption of these practices will require that they are economically attractive and can be adapted to field scales.

Optimal fertilizer nitrogen rates and yield-scaled global warming potential in drill seeded rice

Drill seeded rice ( L.) is the dominant rice cultivation practice in the United States. Although drill seeded systems can lead to significant CH and NO emissions due to anaerobic and aerobic soil conditions, the relationship between high-yielding management practices, particularly fertilizer N management, and total global warming potential (GWP) remains unclear. We conducted three field experiments in California and Arkansas to test the hypothesis that by optimizing grain yield through N management, the lowest yield-scaled global warming potential (GWP = GWP Mg grain) is achieved. Each growing season, urea was applied at rates ranging from 0 to 224 kg N ha before the permanent flood. Emissions of CH and NO were measured daily to weekly during growing seasons and fallow periods. Annual CH emissions ranged from 9.3 to 193 kg CH-C ha yr across sites, and annual NO emissions averaged 1.3 kg NO-N ha yr. Relative to NO emissions, CH dominated growing season (82%) and annual (68%) GWP. The impacts of fertilizer N rates on GHG fluxes were confined to the growing season, with increasing N rate having little effect on CH emissions but contributing to greater NO emissions during nonflooded periods. The fallow period contributed between 7 and 39% of annual GWP across sites years. This finding illustrates the need to include fallow period measurements in annual emissions estimates. Growing season GWP ranged from 130 to 686 kg CO eq Mg season across sites and years. Fertilizer N rate had no significant effect on GWP; therefore, achieving the highest productivity is not at the cost of higher GWP.

An Economic Comparison of Alternative Rice Production Systems in Arkansas

ABSTRACT Weak farm prices, high production costs, and potential future regulation of sediment loadings in waterways force many Arkansas rice producers to consider adopting new management systems to maintain profitability. However, rice producers are reluctant to try new systems without information about the economic outcomes. This paper uses data from a long-term rice-based cropping systems study at Stuttgart, Arkansas to evaluate the profitability and economic risk associated with alternative rice production systems. Economic returns and costs are compared for 40 different rice production systems for the years 2000 and 2001, and statistical analysis is performed to determine which production components (rotation, tillage, fertility, and year) significantly impact rice system net returns. A safety-first criterion is used to identify production systems that would be preferred by risk-averse rice producers. All production components were found to significantly impact rice system net returns during the two-year period. However, the most profitable systems tended to be two-year rice-soybean conventional till systems. These systems exhibited cost savings relative to other systems due to lower production costs for soybeans when compared to rice or corn. Risk analysis indicated that risk-averse rice producers would also prefer using two-year rice soybean conventional till systems to other rice systems. No-till systems were generally less profitable than conventional till systems in 2000 but were generally more profitable than conventional till systems in 2001. No-till may become more economically competitive with conventional till as management improves and soil conditions stabilize over time.

Seasonal Methane and Nitrous Oxide Emissions of Several Rice Cultivars in Direct-Seeded Systems

An understanding of cultivar effects on field greenhouse gas (GHG) emissions in rice ( L.) systems is needed to improve the accuracy of predictive models used for estimating GHG emissions and to evaluate the GHG mitigation potential of different cultivars. We compared CH and NO emissions, global warming potential (GWP = NO + CH), yield-scaled GWP (GWP = GWP Mg grain), and plant growth characteristics of eight cultivars within four study sites in California and Arkansas. Nitrous oxide emissions were negligible (<10% of GWP) and were not different among cultivars. Seasonal CH emissions differed between cultivars by a factor of 2.1 and 1.4 at one California and one Arkansas site, respectively. Plant growth characteristics were generally not correlated with seasonal CH emissions; however, the strongest correlations were observed for shoot and total plant (root + shoot) biomass at heading ( = 0.60) at one California site and for grain at maturity ( = -0.95) at one Arkansas site. Although differences in GWP and GWP were observed, there were inconsistencies across sites, indicating the importance of the genotype × environment interaction. Overall, the cultivars with the lowest CH emissions, GWP, and GWP at the California and Arkansas sites were the lowest and highest yielding, respectively. These findings highlight the potential for breeding high-yielding cultivars with low GWP, the ideal scenario to achieve low GWP, but environmental conditions must also be considered.

An economic risk analysis of no-till management and rental arrangements in Arkansas rice production

Rice is a major cash crop for eastern Arkansas and generally involves intensive cultivation. Sediment is the primary pollutant identified for most eastern Arkansas waterways, and conservation practices like no-till are commonly recommended as remedial mechanisms. The profitability of no-till rice has been investigated, but the main emphasis has been on comparing mean returns of no-till to conventional till without consideration for return variability. Profitability in these studies is also evaluated from the prospective of the producer only, despite the fact that most cropland is owned by someone other than the producer. This study evaluates the profitability and risk efficiency of no-till management in Arkansas rice production from both the perspective of the tenant and the landlord using simulation and stochastic efficiency with respect to a function. Crop yields and prices are simulated for a typical two-year rice-soybean rotation, and tenant and landlord net return distributions are constructed for popular rental arrangements used in eastern Arkansas rice production. The results indicate that both the tenant and the landlord can benefit monetarily from no-till management. Risk-neutral and risk-averse tenants would both benefit from no-till management as no-till increases mean (expected) returns for risk-neutral tenants and results in large risk premiums over conventional till for risk-averse tenants. Risk-neutral landlords would be indifferent between either no-till or conventional till management because mean returns are essentially the same for both tillage methods. Risk-averse landlords would have a slight preference for no-till, since no-till risk premiums tend to be positive with increasing levels of risk aversion. However, no-till risk premiums are modest for risk-averse landlords, implying that risk would play less of a role for the landlord than for the tenant when considering the use of no-till management on rented land.

Water management impacts rice methylmercury and the soil microbiome.

Rice farmers are pressured to grow rice using less water. The impacts of water-saving rice cultivation methods on rice methylmercury concentrations are uncertain. Rice (Oryza sativa L. cv. Nipponbare) was cultivated in fields using four water management treatments, including flooded (no dry-downs), alternating wetting and drying (AWD) (with one or three dry-downs), and furrow-irrigated fields (nine dry-downs) (n=16 fields). Anoxic bulk soil was collected from rice roots during the rice maturation phase, and rice grain was harvested after fields were dried. Total mercury and methylmercury concentrations were determined in soil and polished rice samples, and the soil microbiome was analyzed using 16S (v4) rRNA gene profiling. Soil total mercury did not differ between fields. However, compared to continuously flooded fields, soil and rice methylmercury concentrations averaged 51% and 38% lower in the AWD fields, respectively, and 95% and 96% lower in the furrow-irrigated fields, respectively. Compared to flooded fields, grain yield was reduced on average by <1% in the AWD fields and 34% in the furrow-irrigated fields. Additionally, using 16S (v4) rRNA gene profiling, the relative abundance of genera (i.e., highest resolution via this method) known to contain mercury methylators averaged 2.9-fold higher in flooded and AWD fields compared to furrow-irrigated fields. These results reinforce the benefits of AWD in reducing rice methylmercury concentrations with minimal changes in rice production yields. In the furrow-irrigated fields, a lower relative abundance of genera known to contain mercury methylators suggests an association between lower concentrations of soil and rice methylmercury and specific soil microbiomes.

Crop Performance and Weed Suppression by Weed-Suppressive Rice Cultivars in Furrow- and Flood-Irrigated Systems under Reduced Herbicide Inputs

Abstract Weed control in rice is challenging, particularly in light of increased resistance to herbicides in weed populations and diminishing availability of irrigation water. Certain indica rice cultivars can produce high yields and suppress weeds in conventional flood-irrigated, drill-seeded systems in the southern United States under reduced herbicide inputs, but their response to reduced irrigation inputs in these systems in not known. Rice productivity and weed control by weed-suppressive cultivars and conventional nonsuppressive cultivars were evaluated in a nonflooded furrow-irrigated (FU) system and a conventionally flooded (FL) system under three levels of weed management (herbicide inputs) in a 3-yr field study. Rice yields across all weed management levels yielded ∼ 76% less in the FU system than in the FL system. The allelopathic indica cultivar, ‘PI 312777’, and commercial hybrid rice ‘CLXL729’ generally produced the highest grain yields and greatest suppression of barnyardgrass in both irrigation systems. ‘Bengal’ and ‘Wells’ were the top-yielding conventional cultivars whereas ‘Lemont’ and ‘CL171AR’ yielded the least. Weed suppression by PI 312777 and CLXL729 under “medium” weed management was equivalent to that of Lemont and CL171AR at the “high” management level, suggesting that the weed-suppressive cultivars may be able to compensate for suboptimal herbicide inputs or incomplete weed control. Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) Beauv; rice, Oryza sativa L., ‘Bengal’, ‘CLXL729’, ‘Lemont’, ‘PI 312777’, ‘Wells’.

Impact of production practices on physicochemical properties of rice grain quality

BACKGROUND Rice growers are interested in new technologies that can reduce input costs while maintaining high field yields and grain quality. The bed-and-furrow (BF) water management system benefits farmers through decreased water usage, labor, and fuel as compared to standard flood management. Fertilizer inputs can be reduced by producing rice in rotation with soybeans, a nitrogen-fixing crop, and with the use of slow-release fertilizers that reduce nitrogen volatilization and run-off. However, the influence of these cultural management practices on rice physicochemical properties is unknown. Our objective was to evaluate the influence of nitrogen fertilizer source, water management system, and crop rotation on rice grain quality. RESULTS Grain protein concentration was lower in a continuous rice production system than in a rice-soybean rotation. Neither amylose content nor gelatinization temperature was altered by fertilizer source, crop rotation, or water management. BF water management decreased peak and breakdown viscosities relative to a flooded system. Peak and final paste viscosities were decreased by all fertilizer sources, whereas, crop rotation had no influence on the Rapid Visco Analyser profile. CONCLUSION Sustainable production systems that decrease water use and utilize crop rotations and slow-release fertilizers have no major impact on rice physicochemical properties.

Whole-Farm Evaluation of No-Till Profitability in Rice Production using Mixed Integer Programming

Rice production in Arkansas usually involves intensive tillage. No-till rice has been studied, but the focus has been limited to impacts on yields and per acre returns. This study uses mixed integer programming to model optimal machinery selection and evaluate whole-farm profitability of no-till management, for rice-soybean farms. Results indicate that lower machinery ownership expenses combined with lower fuel and labor expenses do enhance the profitability of no-till management, but the monetary gains appear to be modest, implying that other incentives may be necessary to entice producers to use the practice.

Fall Rice Straw Management and Winter Flooding Treatment Effects on a Subsequent Soybean Crop

ABSTRACT The effects of fall rice (Oryza sativa L.) straw management and winter flooding on the yield and profitability of subsequent irrigated and dryland soybean [Glycine max (L.) Merr.] crops were studied for 3 years. Rice straw treatments consisted of disking, rolling, or standing stubble. Winter flooding treatments consisted of maintaining a minimum water depth of 10 cm by pumping water when necessary, impounding available rainfall, and draining fields to prevent flooding. The following soybean crop was managed as a conventional-tillage system or no-till system. Tillage system treatments were further divided into irrigated or dryland. Results indicated that there were no significant effects from either fall rice straw management or winter flooding treatments on soybean seed yields. Soybean seed yields for the conventional-tillage system were significantly greater than those for the no-till system for the first 2 yrs and not different in the third year. Irrigated soybean seed yields were significantly greater than those from dryland plots for all years. Net economic returns averaged over the 3 yrs were greatest (