Nitrous oxide (N2O) is often the largest single component of the greenhouse‐gas budget of individual cropping systems, as well as for the US agricultural sector as a whole. Here, we highlight the factors that make mitigating N2O emissions from fertilized agroecosystems such a difficult challenge, and discuss how these factors limit the effectiveness of existing practices and therefore require new technologies and fresh ideas. Modification of the rate, source, placement, and/or timing of nitrogen fertilizer application has in some cases been an effective way to reduce N2O emissions. However, the efficacy of existing approaches to reducing N2O emissions while maintaining crop yields across locations and growing seasons is uncertain because of the interaction of multiple factors that regulate several different N2O‐producing processes in soil. Although these processes have been well studied, our understanding of key aspects and our ability to manage them to mitigate N2O emissions remain limited.

Globally, flooding is one of the most damaging abiotic stresses, besides drought, that affects 17 million km 2 of land surface annually. Recent research indicates that climate change is resulting in more extreme weather events, such as flooding or soil waterlogging, that negatively affect crop production. Therefore, it is imperative to understand how flooding stress affects crops and to develop improved production practices that make cropping systems more resilient and able to cope with extreme weather events. This review paper summarizes the current state of knowledge on the impacts of flooding or soil waterlogging on crop production losses, nitrogen (N) losses, and provides potential management strategies to reduce these losses. The factors affecting the extent of flooding injury in plants as well as plant adaptations under waterlogging stress are also discussed briefly. For the purpose of this review, "flooding" refers to the situation when all or part of the plant is submerged under water, whereas "soil waterlogging" refers to the situation where soil pores are saturated with water. Soil waterlogging also promotes soil N losses through runoff, leaching, and denitrification. Potential management practices that can be used to mitigate soil waterlogging stress include the use of flood-tolerant varieties, adjusting management practices, improving drainage, and practicing adaptive nutrient management strategies. However, these might be site-or crop-specific management practices and they should be validated for their economic viability before developing future management plans that promote sustainable crop yields from waterlogged soils.Abbreviations: BMP, Best Management Practice; CDSI, controlled drainage and subirrigation; EEF, enhanced efficiency fertilizer; ET, evapotranspiration; Fv/Fm, ratio of variable fluorescence to material fluorescence; GIS, Geographic Information System; NBPT, N-(n-butyl) thiophosphoric triamide; NI, nitrification inhibitor; NUE, nitrogen use efficiency; PCU, polymer-coated urea; UI, urease inhibitors.This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

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Improvement of N fertilizer recovery effi ciency (NRE) is necessary to reduce excess N entering the environment and to increase economic returns. A 2-yr fi eld trial was established in 2005 in Northeast Missouri to determine the eff ects of conventional and slow-release N fertilizer sources and landscape position (summit, sideslope, and low-lying) on crop growth and NRE in corn (Zea mays L.) in a claypan soil. Nitrogen fertilizer treatments at 168 kg N ha -1 consisted of pre-plant applied and incorporated polymer-coated urea (PCU), urea, 50% PCU/50% urea mix by weight, anhydrous ammonia (AA), and a nontreated control. Gravimetric soil water content data in 2005 and 2006 indicated that the low-lying position was oft en wetter than the summit and sideslope positions. Anhydrous ammonia and PCU treatments increased grain yield 1470 to 1810 kg ha -1 over urea in the lowlying position in 2005 and 2006. Corresponding increases in plant N uptake and NRE were observed in the low-lying position in 2005 with use of PCU and AA compared to urea, but not in 2006. Based on the grain yield results in this research and diff erent fertilizer cost and crop prices, gross profi t diff erences for use of PCU and preplant-applied AA compared with urea in the lowlying position could range from $50 to $642 ha -1 . Th ese results demonstrate that targeted use of diff erent N fertilizer sources in claypan landscapes may increase grain yields and profi tability.

Estimates of N, P, and K availability to corn (Zea mays L.) from injected dairy manure on three field sites in south central Wisconsin were made using a fertilizer equivalence approach. Nutrient uptake from treatments of a control, three rates of manure (approx. 53, 97, and 138 Mg ha−1 yr−1 on a wet basis), and three rates of broadcast fertilizer were evaluated. Crop nutrient recoveries of fertilizer N, P, and K were generally higher than crop recoveries of manure total N, P, and K. Estimates of first year N, P, and K availability showed substantial variability across rate, location, and year with standard deviations often about 50% of the mean. Ranges for N, P, or K availability were 12 to 63, 12 to 89, and 24 to 153%, respectively. These data do not identify those factors responsible for differences in nutrient availability from one site‐year to another. Biological or chemical availability indices of a 1‐wk anaerobic incubation at 40 °C or a 16‐h autoclaving in 0.01 M CaCl2 solution were evaluated as measures of N availability and compared with field results. Correlations between measured changes in NH4‐N from these indices, as well as total Kjeldahl N and inorganic N levels in the top 30 cm of soil 4 to 6 wk after treatment application, and N uptake indicated inorganic N levels to be a better index of N availability than the other indices examined. However, to determine nutrient availability on a routine basis, more reliable biological or chemical indices are necessary. A simple model may help to simulate environmental effects and the contribution of residual nutrients in the soil.