Corn Response to Nitrogen Management under Fully-Irrigated vs. Water-Stressed Conditions

Characterizing corn (Zea mays L.) grain yield (GY) response to N is critical for maximizing profits, increasing N use efficiency and minimizing environmental impacts. Although a large database of GY response to N exists for highly productive soils, few data exist for less productive soils. While changes in precipitation are expected in the future, few studies have compared GY response to varying N management practices under conditions of varying water availability. We measured GY and basal stalk nitrate nitrogen (BSN) at harvest using split-applied urea at eight N rates under fully-irrigated (FI) and water-stressed (WS) conditions in a loamy sand over 2 yr (2009 and 2010). We also measured GY and BSN using single, pre-plant applications of urea, polymer-coated urea (PCU) and urea amended with urease and nitrification inhibitors (IU) at one or two N rates. The results showed that economic optimum nitrogen rate (EONR) and agronomic optimum nitrogen rate (AONR) did not vary by water management, in spite of significant increases in GY (up to 48%) under FI compared to WS. Modification of N fertilizer timing or N source was effective for increasing GY (by 18–41%) with FI, but did not affect GY under WS conditions. Averaged across years, BSN was greater with WS compared to FI at most N rates; however, BSN corresponding to AONR was within the optimal range for both water regimes. These findings may have important implications in areas where changes in irrigation practices or water availability are expected under future climate conditions

Denitrifying Bacteria Active in Woodchip Bioreactors at Low-Temperature Conditions

Woodchip bioreactor technology removes nitrate from agricultural subsurface drainage by using denitrifying microorganisms. Although woodchip bioreactors have demonstrated success in many field locations, low water temperature can significantly limit bioreactor efficiency and performance. To improve bioreactor performance, it is important to identify the microbes responsible for nitrate removal at low temperature conditions. Therefore, in this study, we identified and characterized denitrifiers active at low-temperature conditions by using culture-independent and -dependent approaches. By comparative 16S rRNA (gene) analysis and culture isolation technique, Pseudomonas spp., Polaromonas spp., and Cellulomonas spp. were identified as being important bacteria responsible for denitrification in woodchip bioreactor microcosms at relatively low temperature conditions (15°C). Genome analysis of Cellulomonas sp. strain WB94 confirmed the presence of nitrite reductase gene nirK. Transcription levels of this nirK were significantly higher in the denitrifying microcosms than in the non-denitrifying microcosms. Strain WB94 was also capable of degrading cellulose and other complex polysaccharides. Taken together, our results suggest that Cellulomonas sp. denitrifiers could degrade woodchips to provide carbon source and electron donors to themselves and other denitrifiers in woodchip bioreactors at low-temperature conditions. By inoculating these denitrifiers (i.e., bioaugmentation), it might be possible to increase the nitrate removal rate of woodchip bioreactors at low-temperature conditions

Global Research Alliance N2 O chamber methodology guidelines:Introduction, with health and safety considerations

Non-steady-state (NSS) chamber techniques have been used for decades to measure nitrous oxide (N₂O) fluxes from agricultural soils. These techniques are widely used because they are relatively inexpensive, easy to adopt, versatile, and adaptable to varying conditions. Much of our current understanding of the drivers of N₂O emissions is based on studies using NSS chambers. These chamber techniques require decisions regarding multiple methodological aspects (e.g., chamber materials and geometry, deployment, sample analysis, and data and statistical analysis), each of which may significantly affect the results. Variation in methodological details can lead to challenges in comparing results between studies and assessment of reliability and uncertainty. Therefore, the New Zealand Government, in support of the objectives of the Livestock Research Group of the Global Research Alliance on Agricultural Greenhouse Gases (GRA), funded two international projects to, first, develop standardized guidelines on the use of NSS chamber techniques and, second, refine them based on the most up to date knowledge and methods. This introductory paper summarizes a collection of papers that represent the revised guidelines. Each article summarizes existing knowledge and provides guidance and minimum requirements on chamber design, deployment, sample collection, storage and analysis, automated chambers, flux calculations, statistical analysis, emission factor estimation and data reporting, modeling, and “gap-filling” approaches. The minimum requirements are not meant to be highly prescriptive but instead provide researchers with clear direction on best practices and factors that need to be considered. Health and safety considerations of NSS chamber techniques are also provided with this introductory paper

Maize performance in a kura clover living mulch under drought conditions

Abstract Row establishment is important to mitigate competition with maize (Zea mays L.) seedlings in a kura clover (Trifolium ambiguum Bieb.) living mulch (KCLM). This study investigated the effect of row‐establishment and fertilizer nitrogen (N) rate on maize yield and N uptake in a KCLM system in Arlington, WI, and Rosemount, MN, during the 2021 growing season. Row establishment treatments included rotary zone tillage (RZT), shank strip‐tillage (ST), and banded herbicides (BH), each evaluated at six N rates from 0 to 225 kg N ha−1. Extended periods of moderate and severe drought were experienced during the study period. The Arlington and Rosemount sites received 64 and 63% of the normal precipitation between 20 Apr. and 31 Oct. 2021, but poor distribution and higher temperatures at Rosemount elevated drought severity indices at that site. Grain yields at Rosemount were 3.6 Mg ha−1, whereas Arlington produced yields that matched expectations for the area (10 Mg ha−1). Row establishment affected maize grain yield differentially at each site, where, under severe drought conditions, BH maximized maize yield, whereas under moderate drought conditions, the higher level of tillage (RZT) maximized maize yield. These responses are most likely attributed to reduced moisture loss in the row‐zone of the BH treatment and the greater level of clover suppression in the RZT treatment and their interactions with specific weather conditions at the research sites. Results from this study indicate that row establishment methods in a KCLM cropping system should be considered with spring environmental conditions and the expected weather outlook

Urea Amendment Decreases Microbial Diversity and Selects for Specific Nitrifying Strains in Eight Contrasting Agricultural Soils

Application of nitrogen (N) fertilizers, predominantly as urea, is a major source of reactive N in the environment, with wide ranging effects including increased greenhouse gas accumulation in the atmosphere and aquatic eutrophication. The soil microbial community is the principal driver of soil N cycling; thus, improved understanding of microbial community responses to urea addition has widespread implications. We used next-generation amplicon sequencing of the 16S rRNA gene to characterize bacterial and archaeal communities in eight contrasting agricultural soil types amended with 0, 100, or 500 μg N g-1 of urea and incubated for 21 days. We hypothesized that urea amendment would have common, direct effects on the abundance and diversity of members of the microbial community associated with nitrification, across all soils, and would further affect the broader heterotrophic community resulting in decreased diversity and variation in abundances of specific taxa. Significant (P < 0.001) differences in bacterial community diversity and composition were observed by site, but amendment with only the greatest urea concentration significantly decreased Shannon indices. Expansion in the abundances of members of the families Microbacteriaceae, Chitinophagaceae, Comamonadaceae, Xanthomonadaceae, and Nitrosomonadaceae were also consistently observed among all soils (linear discriminant analysis score ≥ 3.0). Analysis of nitrifier genera revealed diverse, soil-specific distributions of oligotypes (strains), but few were correlated with nitrification gene abundances that were reported in a previous study. Our results suggest that the majority of the bacterial and archaeal community are likely unassociated with N cycling, but are significantly negatively impacted by urea application. Furthermore, these results reveal that amendment with high concentrations of urea may reduce nitrifier diversity, favoring specific strains, specifically those within the nitrifying genera Nitrobacter, Nitrospira, and Nitrosospira, that may play significant roles related to N cycling in soils receiving intensive urea inputs

Kura Clover Living Mulch Reduces Fertilizer N Requirements and Increases Profitability of Maize

Kura clover living mulch (KCLM) systems have been previously investigated for their incorporation into upper Midwestern row crop rotations to provide ecosystem services through continuous living cover. Reductions in soil erosion and nitrate loss to surface and groundwater have been reported, but factors affecting agronomic performance and nutrient management are not well defined. To achieve realized environmental benefits, research must develop agronomic management techniques, determine economic opportunities, and provide management recommendations for row crop production in KCLM systems. Two experiments were conducted in 2017 and 2018 to determine the response to N fertilizer application for maize production in KCLM. The first-year maize experiment followed forage management, and the second-year maize experiment followed maize after forage management. Eight fertilizer N treatments ranging from 0–250 kg N ha−1 were applied to each experiment and grain and stover yields were compared to conventionally managed maize hybrid trials that were conducted nearby. First-year maize did not need fertilizer N to maximize yield and profitability in either growing season, and second-year maize required a fertilizer N rate near local University guidelines for maize following soybean. The net economic return from maize grain and stover in the KCLM averaged over first and second-year maize experiments and 2017 and 2018 growing seasons were $138 ha−1 greater than the conventional comparison

Kura Clover Living Mulch: Spring Management Effects on Nitrogen

Kura clover living mulch (KCLM) systems have the potential to provide ecosystem services in intensively managed cropping systems while supplying soil mineral nitrogen (N) to the growing cash crop. Living mulch management relies on strong spring suppression to reduce competition between vigorous kura clover and emerging row crop seedlings, but standard suppression management practices utilize widely different modes of action. The objective of this research was to gain insight into the impact of common KCLM management practices on early season N dynamics. Kura clover was mowed, and residue was either harvested or returned before rows were established via strip tillage or banded herbicide. Soil and gaseous N pools were monitored for 12 weeks post initial application of suppression management treatments. An enrichment factor (EF) approach was utilized to compare N pools under managed treatments relative to an unmanaged clover control. Strip tillage increased soil N by 300%, while banded herbicide row establishment increased soil N by 220% relative to the unmanaged control. Pre-plant clover harvest reduced short term soil NO3⁻N, but during later time intervals there was no relationship between residue management and soil N. We conclude that, for the dual goals of maintaining clover perenniality while providing greater soil N enrichment, strip tillage is superior to band herbicide for row establishment. Additionally, pre-plant clover harvest may open opportunities for dual harvests in a single growing season, increasing economic return while maintaining in-season N contributions from the living mulch

Soil Water Dynamics and Nitrate Leaching Under Corn–Soybean Rotation, Continuous Corn, and Kura Clover

Improving water quantity and quality impacts of corn ( L.)- and soybean [ (L.) Merr.]-based cropping systems is a key challenge for agriculture in the US Midwest. Long-term field experiments are important for documenting those effects and exploring possible solutions. This study examines differences in soil water dynamics and nitrate-nitrogen (N) leaching among cropping systems and N fertilizer sources in a long-term experiment in southeastern Minnesota. Drainage and leachate concentrations were measured for 4 yr using automated equilibrium tension lysimeters installed below the root zone in replicated, large plots on a well-drained silt loam soil. Soil water storage was monitored using water content reflectometers. Corn–soybean and continuous corn cropping systems exhibited similar soil water dynamics, drainage rates (145–202 mm yr), leachate nitrate N concentrations (21.3–25.6 mg L), and nitrate N leaching loads (30–75 kg ha yr). Nitrate-N concentrations in the leachate were similar whether N was added as urea (21.2 mg L) or anhydrous ammonia (25.7 mg L). A perennial kura clover ( M. Bieb)-based cropping system with no N fertilizer significantly altered soil water dynamics and resulted in lower ( < 0.10) drainage rates (53 mm yr), nitrate N concentrations (7.1 mg L), and nitrate N leaching loads (2–5 kg ha yr) compared with corn–soybean or continuous corn, but also reduced corn grain yields. These impacts are generally consistent with a growing body of literature showing substantial environmental benefits of a kura clover living mulch system for corn production, but the economic viability of such a system is not yet proven

Data from: Identifying environmental drivers of greenhouse gas emissions under warming and reduced rainfall in boreal-temperate forests

1.Atmospheric concentrations of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) are predicted to increase as a consequence of fossil fuel emissions and the impact on biosphere-atmosphere interactions. Forest ecosystems in general, and forest soils in particular, can be sinks or sources for CO2, CH4, and N2O. Environmental studies traditionally target soil temperature and moisture as the main predictors of soil greenhouse gas (GHG) flux from different ecosystems; however, these emissions are primarily biologically driven. Thus, little is known about the degree of regulation by soil biotic vs. abiotic factors on GHG emissions, particularly under predicted increase in global temperatures, and changes in intensity and frequency of precipitation events. 2.Here we measured net CO2, CH4 and N2O fluxes after 5 years of experimental warming (+3.4°C), and 2 years of ≈45% summer rainfall reduction, in two forest sites in a boreal-temperate ecotone under different habitat conditions (closed or open canopy) in Minnesota, USA. We evaluated the importance of microbial gene abundance and climo-edaphic factors (soil texture, canopy, seasonality, climate and soil physicochemical properties) driving GHG emissions. 3.We found that changes in CO2 fluxes were predominantly determined abiotically by temperature and moisture, after accounting for bacterial abundance. Methane fluxes on the other hand, were determined both abiotically, by gas diffusivity (via soil texture) and microbially, by methanotroph pmoA gene abundance, whereas, N2O emissions showed only a strong biotic regulation via ammonia-oxidizing bacteria amoA gene abundance. Warming did not significantly alter CO2 and CH4 fluxes after 5 years of manipulation, while N2O emissions were greater with warming under open canopy. 4.Our findings provide evidence that soil GHG emissions result from multiple direct and indirect interactions of microbial and abiotic drivers. Overall, this study highlights the need to include both microbial and climo-edaphic properties in predictive models in order to provide improved mechanistic understanding for the development of future mitigation strategies