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No-till agriculture represents a relatively widely adopted management system that aims to reduce soil erosion, decrease input costs, and sustain long-term crop productivity. However, its impacts on crop yields are variable, and an improved understanding of the factors limiting productivity is needed to support evidence-based management decisions. We conducted a global meta-analysis to evaluate the influence of various crop and environmental variables on no-till relative to conventional tillage yields using data obtained from peer-reviewed publications (678 studies with 6005 paired observations, representing 50 crops and 63 countries). Side-by-side yield comparisons were restricted to studies comparing conventional tillage to no-till practices in the absence of other cropping system modifications. Crop category was the most important factor influencing the overall yield response to no-till followed by aridity index, residue management, no-till duration, and N rate. No-till yields matched conventional tillage yields for oilseed, cotton, and legume crop categories. Among cereals, the negative impacts of no-till were smallest for wheat (−2.6%) and largest for rice (−7.5%) and maize (−7.6%). No-till performed best under rainfed conditions in dry climates, with yields often being equal to or higher than conventional tillage practices. Yields in the first 1–2 years following no-till implementation declined for all crops except oilseeds and cotton, but matched conventional tillage yields after 3–10 years except for maize and wheat in humid climates. Overall, no-till yields were reduced by 12% without N fertilizer addition and 4% with inorganic N addition. Our study highlights factors contributing to and/or decreasing no-till yield gaps and suggests that improved targeting and adaptation, possibly including additional system modifications, are necessary to optimize no-till performance and contribute to food production goals. In addition, our results provide a basis for conducting trade-off analyses to support the development of no-till crop management and international development strategies based on available scientific evidence. [ABSTRACT FROM AUTHOR]

Highlights: [•] On average, enhanced efficiency nitrogen fertilizers (EENF) led to a 5.7% increase in yield and 8.0% increase in N uptake. [•] The benefit of EENF was related to soil pH with no benefit being observed in acidic soils (pH≤6.0) and enhanced benefit with increasing soil pH. [•] Among the EENF products, NBPT and neem were the most effective while PPD and DCD were the least effective. [•] The effectiveness of EENF was not dependent on N rate, method of first N application, timing of first N application, or water management. [Copyright &y& Elsevier]

Abstract: Flooded rice systems emit both methane (CH4) and nitrous oxide (N2O). Elevated CH4 emissions in rice systems can lead to a high global warming potential (GWP) relative to other crops, thus strategies to reduce greenhouse (GHG) emissions, particularly CH4, are needed. Altering water, residue (carbon) and fertilizer management practices are commonly suggested as options for mitigating GHG emissions in rice systems. While the effects of water and residue management have been reported on elsewhere, the impact of fertilizer management on GHG emissions has not been reviewed quantitatively. We conducted an exhaustive search of peer-reviewed field studies that compared various side-by-side fertilizer management options. Where sufficient studies were available a meta-analysis was conducted to determine average treatment effects of management practices on both CH4 and N2O emissions. Results show that low inorganic fertilizer N rates (averaging 79kgNha−1) increased CH4 emissions by 18% relative to when no N fertilizer was applied, while high N rates (average of 249kgNha−1) decreased CH4 emissions by 15%. Replacing urea with ammonium sulfate at the same N rate significantly reduced CH4 emissions by 40%, but may increase N2O emissions. Overall, the fertilizer-induced emission factor for all inorganic N sources was 0.22%. Dicyandiamide (DCD), a nitrification inhibitor, led to lower emissions of both CH4 (−18%) and N2O (−29%). Limited field data suggest that deep placement of N fertilizer reduces CH4 emissions but increases N2O emissions. When compared to inorganic N fertilizers, farmyard manure (FYM) increased CH4 emissions by 26% and the green manure (GrM) Sesbania by 192%. Neither FYM nor GrM had a significant impact on N2O emissions when compared to an inorganic N treatment at the same N rate. Sulfate fertilizers reduced CH4 emissions by 28% and 53% at average rates of 208 and 992kgSha−1, respectively. These findings demonstrate that a variety of fertilizer management practices affect GHG emissions from rice systems. To develop effective GHG mitigation strategies future work is needed to (i) quantify the effects on GWP (accounting for both CH4 and N2O emissions), (ii) investigate options for combining mitigation practices (e.g. deep placement of ammonium sulfate), and (iii) determine the economic viability of these practices. [Copyright &y& Elsevier]

• Directly-measured percolation in California rice fields ranged from 0.04 to 6.95 cm season-1. • Combined percolation and lateral seepage was 4.4–17.1 cm or 3.4–13.2 % of water inputs. • Reduced flooding (e.g. AWD) has limited potential to reduce water inputs (0.7–2.7 cm season−1). • The rice field water requirement with no surface drainage averages 108 cm season−1. Rice (Oryza sativa) has one of highest applied water footprints of any crop, due in many cases to high percolation and lateral seepage rates in flooded rice fields. Better understanding the magnitude and variability of these subsurface water flows and their contribution to the rice field water balance is critical for efforts to reduce the water footprint of rice production and to limit the transport of pollutants to surface water and groundwater. Percolation was directly measured in eight direct-seeded California rice fields that ranged from 20 to 61% clay and a complete water balance was developed for three of these fields. For these latter fields, directly measured percolation rates were compared to percolation calculated with Darcy's law, and combined percolation and lateral seepage calculated as the residual of a water balance was compared to directly measured values. Across eight fields, cumulative percolation over the growing season ranged from 0.04 to 6.95 cm season−1. The mean cumulative percolation for the three water balance fields was 2.1 cm based on direct measurements compared to 3.2 cm based on Darcy's law calculations. Combined percolation and lateral seepage calculated as the residual term of a water balance for the three fields was 17.1 cm, compared to 4.4 cm based on direct measurements, corresponding to 13.2 % and 3.4 % of water inputs, respectively (inputs were 98–99 % from irrigation). Based on these results, water management strategies that remove floodwater (e.g. alternate wetting and drying) would have limited potential to reduce water inputs in California rice production (0.7–2.7 cm season-1). Furthermore, using the most conservative (largest) estimates for each component of the water balance, we conclude that the average water requirement for California rice fields is approximately 108 cm season-1. [ABSTRACT FROM AUTHOR]

Soil microorganisms are considered a sensitive indicator of soil health and quality. In cropping systems, soil microorganisms are strongly affected by crop management, including the application of fertilizers. While studies in natural ecosystems have generally found that increased nitrogen (N) inputs decrease microbial biomass, microorganisms in soils under upland crops often benefit from mineral fertilizer input. Paddy rice soils, being flooded for part of the season, are dominated by different carbon (C) and N cycle processes and microbial communities than soils under upland crops. The objective of this study was to explore the effect of fertilizer on soil microorganisms in paddy rice systems in a meta-analysis of the peer-reviewed literature. Across all studies (n = 55), the addition of mineral fertilizer significantly increased microbial biomass carbon content (MBC) by 26% in paddy rice soils. Mineral fertilizer applications also increased soil organic carbon content (SOC) by 13%. The higher crop productivity with fertilization likely led to higher organic C inputs, which in turn increased SOC and MBC contents. The time of sampling within a season (pre-plant rice, in-season rice, post-harvest rice, or post-harvest rotational crop) did not significantly affect the response of MBC to mineral fertilizer. The positive effect of mineral fertilizer on MBC content did not differ between cropping systems with continuous rice and systems where paddy rice was grown in rotation with other crops. However, compared with upland cropping systems, the increase in the microbial biomass due to mineral fertilizer application is more pronounced in rice cropping systems, even when rice is grown in rotation with an upland crop. Differences in climate and soil oxygen availability likely explain the stronger response of soil microorganisms to mineral fertilizer input in paddy rice systems. Our analysis suggests that fertilization does not consistently select for specific microbial groups (e.g. gram positive or negative bacteria, fungi, actinomycetes) in paddy rice systems; however, it affects microbial community composition through changes in soil properties. How specific groups of microorganisms respond to mineral fertilization likely depends on environmental factors. Overall, our results suggest that in paddy rice systems the application of inorganic fertilizers increases SOC and MBC contents, both of which are important indicators of soil health. [ABSTRACT FROM AUTHOR]

Rice systems provide a major source of calories for more than half of the world’s population; however, they also use more water than other major crops. Alternate wetting and drying (AWD) is an irrigation practice (introduction of unsaturated soil conditions during the growing season) that can reduce water inputs in rice, yet it has not been widely adopted, in part, due to the potential for reduced yields. We conducted a meta-analysis to: 1) quantify the effect of AWD on rice yields and water use; and 2) to identify soil properties and management practices that favor AWD yields and promote low water use relative to continuous flooding (CF- control). We analyzed 56 studies with 528 side-by-side comparisons of AWD with CF. Overall, AWD decreased yields by 5.4%; however under Mild AWD (i.e. when soil water potential was ≥ −20 kPa or field water level did not drop below 15 cm from the soil surface), yields were not significantly reduced in most circumstances. In contrast, Severe AWD (when soils dried beyond −20 kPa) resulted in yield losses of 22.6% relative to CF. These yield losses were most pronounced in soils with pH ≥ 7 or carbon < 1% or when AWD was imposed throughout the season. While water use was lowest under Severe AWD, under Mild AWD water use was reduced by 23.4% relative to CF. Our findings both highlight the potential of AWD to reduce water inputs without jeopardizing yield as well as the conditions under which these results can be realized. [ABSTRACT FROM AUTHOR]

The temporal and spatial variations in greenhouse gas (GHG) emission estimates in wetlands impede our ability to predict and upscale total emissions; thus, a scalar parameter is needed to predict GHG emissions. We investigated the importance of soil organic carbon (SOC) in the prediction of methane (CH 4 ) and nitrous oxide (N 2 O) emissions in rewetted agricultural peatlands, positing that both CH 4 and N 2 O production are explained by the quantity and turnover of SOC. Field CH 4 and N 2 O fluxes, along with other edaphic and environmental variables, were monitored in rewetted peatlands with a range of SOC (6%, 11%, and 23%) that were recently converted from row crops to flooded rice cultivation to reverse soil subsidence. Nitrogen (N) fertilization reduced annual CH 4 emission by 77.2% in the 6% C field, but this effect was not found in other fields. Annual N 2 O emissions were not affected by N fertilization and averaged 8.9, 5.2, and 1.9 kg N 2 O-N ha −1 for the 6%, 11%, and 23% C fields, respectively. SOC was the dominant factor controlling both CH 4 and N 2 O emissions. The annual emission for both CH 4 and N 2 O was accurately described by a decaying power regression with increasing SOC contents ( R 2 > 0.49). This relationship was also observed after splitting total annual emission of CH 4 and N 2 O into growing and fallow seasons. Nitrogen fertilization and the seasonality in CH 4 and N 2 O emissions did not change the relationships. The inverse correlation between SOC and CH 4 and N 2 O emissions was likely caused by different chemical composition of SOC in various soils. Our results suggest that SOC can be a potential proxy to predict CH 4 and N 2 O emissions in rewetted peatlands to better define GHG predictions of wetland restoration efforts. [ABSTRACT FROM AUTHOR]

Conservation agriculture (CA) has been promoted as a method of sustainable intensification and climate change mitigation and is being widely practiced and implemented globally. However, no-till (NT), a fundamental component of CA, has been shown to reduce yields in many cases. In order to maintain yields following adoption of CA, it has been recently suggested that fertilizer application should be an integral component of CA. To determine the contribution of nitrogen (N) fertilizer in minimizing yield declines following NT implementation, we assessed 2759 paired comparisons of NT and conventional tillage (CT) systems from 325 studies reported in the peer-reviewed literature between 1980 and 2013. Overall, we found that NT yields decreased −10.7% (−14.8% to −6.5%) and −3.7% (−5.3% to −2.2%) relative to CT in tropical/subtropical and temperate regions, respectively. Among management and environmental variables that included: the rate of N fertilization; the duration of the NT/CT comparison; residue, rotation, and irrigation practices; the crop type; and the site aridity, N rate was the most important explanatory variable for NT yield declines in tropical/subtropical regions. In temperate regions, N fertilization rates were relatively less important. NT yield declines were most consistently observed at low rates of N fertilization during the first 2 years of NT adoption in tropical/subtropical regions. Applications of N fertilizer at rates of up to 85 ± 12 kg N ha −1 yr −1 significantly reduced NT yield declines in these scenarios. While this result should not be viewed as a rate recommendation, it does suggest that farmers applying rates of N fertilizer that are low for their specific system will, on average, see higher NT yields if they increase application rates. In addition, when crop rotation was not practiced or residues were removed from the field, NT yield declines were magnified by low rates of N fertilization in tropical/subtropical regions. These results, based on a global data set and across a broad range of crops, highlight the importance of N fertilization in counteracting yield declines in NT systems, particularly in tropical/subtropical regions. [ABSTRACT FROM AUTHOR]

• Midseason drainage decreased CH 4 emissions by 38–66% compared to CF. • High soil-drying severity reduced CH 4 emissions and GWP by 64% compared to CF. • For every 1% reduction in soil GWC, CH 4 emissions were reduced by 2.5%. • N 2 O emissions accounted for only 0.5% of seasonal GWP across drainage treatments. • Drainage did not significantly affect grain yield compared to CF within each year. Rice (Oryza sativa L.) cultivation is an important part of global food security, yet it is also responsible for a significant portion of agricultural greenhouse gas (GHG) emissions, particularly methane (CH 4). Midseason drainage of flooded rice fields can decrease CH 4 emissions, but the magnitude of CH 4 reduction and its effect on grain yield are variable due to variation in the timing and soil-drying severity of drainage across studies. Therefore, in this two-year study, we aimed to quantify the effect of timing and severity of a single midseason drainage event on seasonal GHG emissions and grain yields, compared to a continuously flooded (CF) control. Treatments varied in terms of soil-drying severity (low, medium, and high, corresponding to approximately 5, 8, and 12 days of drying, respectively) and the timing of when drainage events occurred (between 34–49 and 45–59 days after seeding, or roughly between tillering and panicle initiation). Soil moisture parameters (perched water table, volumetric water content, gravimetric water content (GWC), and soil water potential), soil mineral nitrogen, CH 4 and nitrous oxide (N 2 O) emissions, grain yield, and yield components were all quantified. Midseason drainage reduced seasonal CH 4 emissions by 38–66%, compared to the CF control. Seasonal CH 4 emissions decreased with increasing drain severity, and for every 1% reduction in soil GWC during the drainage period, seasonal CH 4 emissions were reduced by 2.5%. The timing of drainage had no significant impact on CH 4 emissions. Emissions of N 2 O were low (average = 0.035 kg N 2 O-N ha−1) and accounted for only 0.5% of the seasonal global warming potential (GWP) across all drainage treatments. Within each year, drainage did not significantly affect grain yield compared to the CF control. Additionally, midseason drainage reduced both GWP and yield-scaled GWP by approximately the same amount as seasonal CH 4 emissions, as N 2 O emissions were minimal and yields were similar across treatments. These results indicate that midseason drainage may be a viable GHG mitigation practice in flooded rice systems with limited risk for yield reduction, however, this practice should also be further tested under a broad range of soil types and different environments to determine its widespread adoptability. [ABSTRACT FROM AUTHOR]

Highlights • A meta-analysis on GHG emissions and rice yield as affected by water management. • Non-continuous flooding reduced CH 4 emissions by 53%, but it increased N 2 O emissions by 105%. • Severe soil drying reduced rice yield, but mild soil drying did not. • Non-continuous flooding reduced GWP by 44% and yield-scaled GWP by 42%. • IPCC underestimates the impact of multiple (i.e. ≥ 2) drying events on CH 4 emissions. Abstract Rice is a main staple food for roughly half of the world's population, but rice agriculture is also a main source of anthropogenic greenhouse gas (GHG) emissions. Many studies have reported that water management (e.g. alternate wetting and drying, intermittent irrigation, mid-season drain, aerobic rice) affects rice yields and methane (CH 4) and nitrous oxide (N 2 O) emissions from rice paddies. However, these studies span a variety of practices and vary in experimental design and results, making it difficult to determine their global response from individual experiments. Here we conducted a meta-analysis using 201 paired observations from 52 studies to assess the effects of water management practices on GHG emissions and rice yield. Overall, compared to continuous flooding, non-continuous flooding practices reduced CH 4 emissions by 53%, increased N 2 O emissions by 105%, and decreased yield by 3.6%. Importantly, N 2 O emissions were low, contributing, on average, 12% to the combined global warming potential (GWP; CH 4 + N 2 O). As a result, non-continuous flooding reduced GWP (-44%) and yield-scaled GWP (-42%). However, non-continuous flooding practices stimulated N 2 O emissions to a greater degree in soils with high organic carbon or with manure additions. The reduction in CH 4 emissions increased with the number of drying events, soil drying severity, and the number of unflooded days. Currently, Intergovernmental Panel on Climate Change (IPCC) scaling factors for single and multiple (≥ 2) drying events are 0.6 and 0.52. Based on this analysis using actual side-by- side field studies, we suggest changing these to 0.67 for a single event and 0.36 for multiple events. [ABSTRACT FROM AUTHOR]

Highlights • Safe AWD does not mitigate As accumulation in rice compared to CF. • AWD25 and AWD35 similarly lead to a 41-68% decrease in grain As compared to CF. • AWD25 and AWD35 are effective in reducing the late season accumulation of As. • AWD35 can minimize Cd and As uptake simultaneously in this study. Abstract Alternate wetting and drying (AWD) irrigation can be used to promote oxic soil conditions and decrease arsenic (As) mobility and uptake into rice plants. However, scant information is available quantifying plant As speciation and uptake at the field scale for AWD with different soil drying severities. It is hypothesized that as the severity of soil drying increases, plant uptake and subsequent accumulation of both inorganic and organic As in the grain will decrease. However, since AWD can increase cadmium (Cd) bioavailability, Cd concentrations in rice grains should be evaluated concomitant to As. In this two-year field study, As and Cd uptake were examined, with routine plant and water sampling during the growing seasons, under three AWD practices varying in soil drying severity (from most to least severe: AWD25: drying to 25% volumetric water content at the root zone; AWD35: to 35%; AWDS: Safe AWD, drying to perched water table 15 cm below the soil surface), compared to a continuous flooding (CF) control. Arsenic speciation was also analyzed in grain and vegetative tissues. AWD25 and AWD35 decreased As accumulation in roots and straws by a similar amount compared to CF, leading to a 41-68% decrease in grain total As concentration. Speciation analysis revealed that AWD25 and AWD35 decreased grain concentration of organic As by 70-100% and inorganic As by 14-61% compared to CF. In contrast, AWDS did not decrease As uptake by rice compared to CF. Grain Cd levels were 6.5 μg kg−1 in CF, 16.6 μg kg−1 in AWD35, and 27.4 μg kg−1 in AWD25, suggesting AWD35 could serve as a mitigation option for As, while minimizing Cd accumulation. [ABSTRACT FROM AUTHOR]

Abstract The accumulation of arsenic (As) in rice grain is a public health concern since As is toxic to humans; in particular, inorganic As can cause many chronic diseases including cancer. Rice crops are prone to accumulating As, in part, due to the anaerobic soil conditions triggered by the traditional continuously flooded irrigation practice. The objective of this study was to determine how the severity and the timing (i.e. crop stage) of a single soil drying period impact total As concentration and As speciation within the rice (both white and brown) grain, compared to a continuously flooded (CF) control. Drying the soil until the perched water table reached 15 cm below the soil surface (same severity as in the "Safe Alternate Wetting and Drying"), which in this study corresponded to a soil (0–15 cm) water potential of ~0, did not decrease grain As concentrations, regardless of timing. Drying the soil to Medium Severity [MS: soil (0–15 cm) water potential of −71 kPa] or High Severity [HS: soil (0–15 cm) water potential of −154 kPa] decreased total As by 41–61%. However, inorganic As did not always decrease because the severity and the timing of soil drying affected As speciation within the grain. Overall, the soil had to be dried to HS and/or late in the growing season (i.e., at booting or heading instead of at panicle initiation) to decrease inorganic As concentration in the rice grain. This study indicates that the imposition of a single soil drying period within the growing season can mitigate As accumulation in rice grain, but it depends on the severity and timing of the drying period. Further, irrigation management affects As speciation within the rice grain and this must be considered if regulations on inorganic As are based on a percentage of total As measured. Graphical abstract Unlabelled Image Highlights • Continuously flooded irrigation favors the accumulation of arsenic in rice grain. • Treatments with one soil drying period differing in timing and severity were tested. • Across all timings, severe soil drying (≤−71 kPa) decreased total As concentration. • However, inorganic As (the most toxic to humans) not always decreased. • Irrigation management affects both total As and As speciation within rice grain. [ABSTRACT FROM AUTHOR]

Continuously flooded rice systems are a major contributor to global rice production and food security. Allowing the soil to dry periodically during the growing season (such as with alternate wetting and drying irrigation - AWD) has been shown to decrease methane emissions, water usage, and heavy metal accumulation in rice grain. However, the effects of AWD on rice yields are variable and not well understood. A two-year study was established to quantify the impacts of a range of treatments differing in AWD severity (degree of soil drying between flooding events) on yield (as well as factors that may affect yields), soil hydrology in the soil profile, and grain arsenic (As) concentrations relative to a continuously flooded control (CF). Three AWD treatments of increasing severity were imposed between full canopy cover (around 45 days after sowing) and 50% heading: AWD-Safe (field was reflooded when the perched water table reached 15 cm below the soil surface) and AWD35 and AWD25 (field was reflooded when the soil volumetric water content at 0–15 cm depth reached 35% and 25%, respectively). During the drying periods, the 0–15 cm soil layer in the AWD-Safe remained saturated, whereas in AWD35 and AWD25 the soil dried to the desired volumetric water contents. In contrast, soil moisture at 25–35 cm below the soil surface was similar across all treatments. Yield was not reduced in any of the AWD treatments, compared to the CF control. There were no consistent differences in yield components, 13 C discrimination, and N dynamics. Results suggest that the availability of water and the presence of roots at the 25–35 cm soil depth during the drying periods ensured that the crop did not suffer drought stress and thus yields were maintained. Grain As concentration in the AWD-Safe treatment was similar to that in the CF control but decreased by 56–68% in AWD35 and AWD25. AWD-Safe is often promoted as a means of practicing AWD without reducing yields; however, in this study this practice did not reduce grain As concentration because the soil did not reach an unsaturated state. These findings demonstrate that knowledge of surface and subsurface hydrology, and the root system are important for understanding the potential of AWD. [ABSTRACT FROM AUTHOR]

Meeting the challenge of feeding a growing population with limited resources will require increasing the yield potential of staple crops, such as rice. Yet many high-yielding, intensive production systems have experienced slow rates of yield improvement in recent years despite a demonstrated increase in the yield potential of new crop cultivars. We analyzed experimental data from one such cropping system, i.e., California (CA) rice, in order to quantify improvements made in the genetic yield potential obtained through plant breeding. California rice systems are among the highest in the world and close to maximum yield potential. Specifically, the hypothesis was tested that if rice cultivar yields decline over time then apparent yield increases in side-by-side yield comparison tests will not reflect increases in yield potential. This hypothesis was tested using 33 years of experimental yield data from the California Cooperative Rice Research Foundation Rice Experiment Station. Based on side-by-side comparisons of old and new rice cultivars which do not consider yield decline over time, there was an apparent increase in yield. However, the yields of older cultivars were found to decline at an estimated rate of 29.3 kg ha −1 year −1 (90% credible interval −4.4 to −53.3) after initial selection. Once this effect was considered, the yield advantage of newer cultivars over old was uncertain (−3.3 kg ha −1  year −1 , 90% credible interval −36.1 to 31.5). These results highlight (1) the importance of continuous crop improvement and deployment of new cultivars simply to maintain existing yields, and (2) to increase the genetic yield potential, higher yield targets are needed. Importantly, when breeding near the yield potential, despite the limited yield gains, significant advances in improving quality and reducing crop duration have been made. [ABSTRACT FROM AUTHOR]

Worldwide, rice systems are faced with the challenge of producing higher yields with less water. Water savings practices such as aerobic system and alternate wetting and drying (AWD) are being evaluated in lowland rice systems. However, few studies have been conducted on this subject in tropical South America where soils are highly weathered. Thus, a three-year field experiment was conducted in Brazil on a lowland Plinthaquults to investigate crop performance, water input productivity (WP in ) and N recovery under five irrigation regimes: continuous flooding (CF); AWD with short cycle (AWDS); AWD with long cycle (AWDL); saturated soil without ponded water (SS); and aerobic (AR). The drying events in AWDS occurred more frequently than in AWDL. The experimental design was a split-plot with irrigation regimes in the main plot and N fertilizer rate, 0 or 150 kg N ha −1 , in the subplot. 15 N micro-plots were set up to examine the fate of N fertilizer. The highest grain yields for 150N and 0N treatments resulted from the AR irrigation regime and averaged 9.1 and 6.5 mg ha −1 , respectively. Yields among the others irrigations regimes varied from year to the next, but the average was 8.5 and 5.4 mg ha −1 in the 150N and 0N treatments, respectively. Higher yields are attributed to higher N uptake and greater N recovery in the AR treatment. Apparent N recovery averaged 58% in the AR treatment compared to 34% in the other treatments. Similarly, total recovery (plant and soil) of 15 N in the AR treatment was 82%, compared to 62, 61, 56, 56% in SS, AWDS, AWDL, CF respectively. Higher N recovery in the AR was likely the result of lower N losses. Irrigation inputs ranged from 15 mm in the AR to 1337 mm in the CF treatment. The WP in (kg m −3 ) averaged 0.8 in AR, and 0.5, 0.4, 0.5 and 0.4 in SS, CF, AWDS, AWDL and CF. Thus, in this environment, rice productivity, water productivity, and N use efficiency were all enhanced in aerobic systems relative to continuous flooding or any alternative irrigation regime. [ABSTRACT FROM AUTHOR]

The scarcity of high quality irrigation water is a global issue facing rice growers, forcing many to adopt water management systems that may result in increased salinity and yield reductions. While salt concentrations in field water have been shown to vary depending on water management, the distribution and build-up patterns of dissolved salts are unclear. This study was conducted to elucidate the within field spatial and temporal salinity dynamics in water-seeded rice cropping systems, and to assess current salinity thresholds for rice yield reduction. In this two-year study, water and soil salinity concentrations of eleven field sites were monitored weekly, with three sampling points being established in the top, middle and bottom basins of each field. There was a consistent spatio-temporal water salinity pattern among all fields: the maximum water salinity within a field occurred during week 2 to week 7 after planting, and was greatest farther from the irrigation inlet and where soil salinity was high. A model developed to predict water salinity within a field indicates that, averaged over an entire growing season, the position within a field contributed to 82% of the variation explained by the model, while preseason soil salinity contributed to 18%. Importantly, field water salinity was determined to be the most sensitive salinity metric for rice yield, as preseason soil salinity was a poor predictor of yield loss. The threshold field water salinity concentration was estimated at 0.88 dS m −1 , lower than the previous report of 1.9 dS m −1 . These results illustrate the ability to predict water salinity in a rice field with few parameters, while highlighting the importance of field water salinity as the main salinity metric for rice cropping systems. [ABSTRACT FROM AUTHOR]

Many assessments of crop yield gaps based on comparisons to actual yields suggest grain yields in highly intensified agricultural systems are at or near the maximum yield attainable. However, these estimates can be biased in situations where yields are below full yield potential. Rice yields in the US continue to increase annually, suggesting that rice yields are not near the potential. In the interest of directing future efforts towards areas where improvement is most easily achieved, we estimated yield potential and yield gaps in US rice production systems, which are amongst the highest yielding rice systems globally. Zones around fourteen reference weather stations were created, and represented 87% of total US rice harvested area. Rice yield potential was estimated over a period of 13–15 years within each zone using the ORYZA(v3) crop model. Yield potential ranged from 11.5 to 14.5 Mg ha −1 , while actual yields varied from 7.4 to 9.6 Mg ha −1 , or 58–76% of yield potential. Assuming farmers could exploit up to 85% of yield potential, yield gaps ranged from 1.1 to 3.5 Mg ha −1 . Yield gaps were smallest in northern California and the western rice area of Texas, and largest in the southern rice area of California, southern Louisiana, and northern Arkansas/southern Missouri. Areas with larger yield gaps exhibited greater annual yield increases over the study period (35.7 kg ha −1 year −1 per Mg yield gap). Adoption of optimum management and hybrid rice varieties over the study period may explain annual yield increases, and may provide a means to further increase production via expanded adoption of current technologies. [ABSTRACT FROM AUTHOR]

Rice ( Oryza sativa L.) cultivation is critically important for global food security, yet it also represents a significant fraction of agricultural greenhouse gas (GHG) emissions and water resource use. Alternate wetting and drying (AWD) of rice fields has been shown to reduce both methane (CH 4 ) emissions and water use, but its effect on grain yield is variable. In this three-year study we measured CH 4 and nitrous oxide (N 2 O) emissions, rice grain total arsenic (As) concentrations, yield response to N rate, and grain yield from two AWD treatments (drill-seeded and water-seeded) and a conventionally managed water-seeded treatment (control). Grain yields (average = 10 Mg ha −1 ) were similar or higher in the AWD treatments compared to the control and required similar or lower N rates to achieve these yields. Furthermore, AWD reduced growing season CH 4 emissions by 60–87% while maintaining low annual N 2 O emissions (average = 0.38 kg N 2 O–N ha −1 ); N 2 O emissions accounted for <15% of the annual global warming potential (GWP) in all treatments. Fallow season emissions did not vary by treatment and accounted for 22–53% of annual CH 4 emissions and approximately one third of annual GWP on average. The AWD treatments reduced annual GWP by 57–74% and growing season yield-scaled GWP by 59–88%. Milled grain total As, which averaged 0.114 mg kg −1 in the control, was reduced by 59–65% in the AWD treatments. These results show that AWD has the potential to mitigate GHG emissions associated with rice cultivation and reduce rice grain total As concentrations without sacrificing grain yield or requiring higher N inputs; however future research needs to focus on adapting AWD to field scales if adoption of this technology is to be realized. [ABSTRACT FROM AUTHOR]

Accurate estimation of a crop’s yield potential (Yp) is critical to addressing long-term food security via identification of the exploitable yield gap. Due to lack of field data, efforts to quantify crop yield potential typically rely on crop models. Using the ORYZA rice crop model, we sought to estimate Yp of irrigated rice for two widely used rice varieties (M-206 and CXL745) in three major US rice-producing regions that together represent some of the highest yielding rice regions of the world. Three major issues with the crop model had to be addressed to achieve acceptable simulation of Yp; first, the model simulated leaf area index (LAI) and biomass agreed poorly for all direct-seeded systems using default settings; second, cold-induced sterility and associated yield losses were poorly simulated for environments with a large diurnal temperature variation; lastly, simulated Yp was sensitive to the specified definition of physiological maturity. Except for the simulation of cold-induced sterility, all issues could be remedied within the existing model structure. In contrast, simulation of cold-induced sterility posed a continuing challenge to accurate simulation—one that will likely require changes to ORYZA's formulation. Estimates of Yp from the modified model were validated against large multi-year data sets of experimental yields covering the majority of US rice production areas. Validation showed the adjusted model simulated Yp well, with most top yields falling within 85% of Yp for both varieties (77% and 78% observed yields within 15% of Yp for CXL745 and M-206 respectively). Maximum estimated Yp was 14.3 (range of 8.2–14.5) and 14.5 (range of 8.7–15.3) t ha ‐1 for the Southern US and CA, respectively. [ABSTRACT FROM AUTHOR]

The nexus of climate change and food security challenges currently facing humanity requires better understanding of how to balance food production needs with climate change mitigation. Life cycle assessment methods provide a way to quantify the climate impacts of a food product by accounting for all greenhouse gas (GHG) emissions associated with its production, including upstream and downstream from the farm. This study modeled life cycle GHG emissions for one kg of milled, unpackaged rice produced in California, USA, a state that achieves some of the highest rice yields in the world. The goal was to (1) provide an assessment of life cycle GHG emissions of a comparatively intensive production system, using local field emissions data, (2) identify emissions hotspots, and (3) create a model that elucidates the life cycle-wide consequences of potential changes in field management practices. Study parameters are based on an annual cropping cycle, with continuous flooding during the growing season and soil incorporation of straw post-harvest, and yields of 9.3 Mt ha −1 dried paddy rice. Field emissions (growing and fallow seasons) were estimated with empirical data while other emissions were calculated using an engineering model coupled with life cycle inventory datasets and vehicle emission models. The 100-year global warming potential (GWP, based on CO 2 , CH 4 and N 2 O) was 1.47 kg CO 2 -equivalent (CO 2 e) kg −1 of milled rice; of which field emissions contributed 69%. These results are relatively low when compared to life cycle studies in other parts of the world, due in large part to higher grain yields and lower field emissions. When using IPCC Tier 1 estimates of field emissions, the GWP increased to 3.60 CO 2 e kg −1 rice, highlighting the importance of using direct field measurements as we have in this study. Due to their large contributions to life cycle GWP, reducing field CH 4 emissions through different field management practices, optimizing N fertilizer use, and increasing fuel efficiency or reducing use of farm machinery present the greatest opportunities to reduce life cycle emissions. Because of high variability and uncertainty in estimating field emissions, they should also be targeted for improved measurement and modeling. [ABSTRACT FROM AUTHOR]

Highlights: [•] Significant responses to N fertilization were observed for all crops in all years. [•] Miscanthus and switchgrass achieved the highest fertilized and unfertilized yields. [•] Miscanthus and switchgrass had the highest fertilizer responses and FUE. [•] Miscanthus and switchgrass have most potential as dedicated energy crops. [ABSTRACT FROM AUTHOR]

Highlights: [•] Annual yield-scaled GWP of water-seeded rice assessed in on-farm study. [•] Nonlinear increase in seasonal N2O emissions in response to N rate observed. [•] Seasonal CH4 emissions increased with fertilizer N addition (except at 260kgNha−1). [•] Annual GWP increased with N rate up to 140kgNha−1. [•] Yield-scaled GWP was minimized at N rates that produced optimal yields. [ABSTRACT FROM AUTHOR]

Abstract: In water-seeded rice systems, cyanobacteria (Nostoc spongiaeforme) hinder early-season crop growth by dislodging and reducing light to seedlings. Since algae are often phosphorus (P) limited, we investigated whether changing the timing of P fertilizer application could reduce algal growth without reducing crop yields or increasing mid-season water P concentrations to levels of concern for water quality. Water P and algae were monitored in 10 and 12 (respectively) side-by-side fields (16–60ha in size) where P fertilizer was applied pre-plant or where P application was delayed until after rice plants had emerged above the surface of the floodwater (2–5 weeks after seeding). Early-season water P concentration and algal occurrence were higher (P <0.001 and P =0.018, respectively) when P fertilizer was applied pre-plant as opposed to delayed. In fields receiving a delayed P application, water P increased to as high as 1.68mgL−1 immediately following application and subsequently declined by 0.054mgL−1 day−1 (P =0.029). A separate study evaluated the effect of P fertilizer timing on crop productivity and P uptake. Triple-super-phosphate was either not applied or was applied to the soil surface in the fall prior to the cropping season, immediately prior to planting, 35 days after seeding (DAS) and 49 DAS at a rate of 25kgha−1 P. P uptake and agronomic P use efficiency (APUE) were similar when P was applied at seeding or 35 DAS. However, relative to P application at seeding, yields were reduced by 6% and there was lower APUE when P was applied after harvesting the previous crop or at 49 DAS (P <0.05). These results indicate that correctly timed, delayed fertilizer P applications can maximize rice yield while reducing early-season interference from algae. However, because delayed applications of P fertilizer also increased water P concentrations, drainage water must be managed carefully following application. [Copyright &y& Elsevier]

Growing public concern over agricultural nitrogen (N) pollution is now reflected in consumers' food choices and shareholders' resolutions, causing rapid changes in global food supply chains. Nitrate (NO 3) leaching represents the primary N source for groundwater contamination and freshwater ecosystem degradation. However, simplified science-based indicators are still lacking to facilitate improved N management practices at the farm-level. We conducted a global analysis of published field studies to evaluate N balance (N inputs minus N outputs) as a robust predictor for NO 3 losses. Using 82 studies (1110 observations) for rainfed cereal crops in temperate regions, we 1) quantified the response of NO 3 losses to changes in N balance for major rainfed cereal crops while accounting for environmental and management variables; and 2) assessed the feasibility of improving water quality through lower N balance under different scenarios using the case study of maize (Zea mays L.) data from the US Corn Belt. Observations were grouped in studies from the US and non-US regions. Results show that NO 3 losses increased exponentially as N balance increases for both the US and non-US regions, though they were 60% higher in the US at a given N balance. Scenario analysis revealed that reducing the N rate from the agronomic optimum to the lower point within the economic optimum N rate range decreased NO 3 losses by 13% without impacting economic returns. The case study for maize showed that improvements in N use efficiency that increase grain yield at a given fertilizer rate can substantially reduce N balance and mitigate NO 3 losses. This study provides an evidence-based foundation for food supply chain companies to mitigate global NO 3 pollution, specifically by using the generalized relationships presented here to track progress in NO 3 leaching mitigation. To further resolve uncertainties and improve region-specific estimates for NO 3 losses, we propose a tiered monitoring and assessment framework similar to the IPCC (Intergovernmental Panel on Climate Change) methodology for N 2 O emissions, widely implemented in science and used for policy. • A global analysis was conducted to evaluate N balance (N inputs minus N outputs) as a predictor for NO 3 losses. • The response of NO 3 losses to changes in N balance were quantified for the US as compared to non-US cropping systems. • NO 3 losses increased exponentially as N balanced increased, for both the US and non-US regions. • This study provides an evidence-based foundation for food supply chain companies to mitigate and track NO 3 pollution. [ABSTRACT FROM AUTHOR]