Although salinity and sodicity are worldwide problems, information on greenhouse gas (GHG) emissions from agricultural salt-affected soils is scarce. The CO 2 -C and N 2 O-N emissions were quantified from three zones intertwined within a single U.S.northern Great Plains field: a highly productive zone (electrical conductivity with 1:1 soil/water mass ratio [EC 1:1 ] = 0.4 dS m -1 ; sodium adsorption ratio [SAR] = 1.8), a transition zone (moderately salt-affected; EC 1:1 = 1.6 dS m -1 ; SAR = 4.99), and a saline/sodic zone (EC 1:1 = 3.9 dS m -1 ; SAR = 22). In each zone, emissions were measured every 4 h for 7 d in four randomly placed chambers that were treated with two N rates (0 and 224 kg N ha -1 ). The experiment was conducted in 2018 and 2019 during similar seasonal periods. Soil samples taken from treatments after GHG measurement were analyzed for soil inorganic N, and microbial biomass from different communities was quantified using phospholipid fatty acid analysis. Realtime polymerase chain reaction was used to quantify the number of copies of some specific denitrification functional genes. The productive zone had the highest CO 2 -C, the lowest N 2 O-N emissions, and the greatest microbial biomass, whereas the saline/sodic zone had the lowest CO 2 -C, the highest N 2 O-N emissions, and the lowest microbial biomass. Within a zone, urea application did not influence CO 2 -C emissions; however, N 2 O-N emissions from the urea-treated saline/sodic zone were 84 and 57% higher than from the urea-treated productive zone in 2018 and 2019, respectively. The copy number of the nitrite reductase gene, nirS, was 42-fold higher in the saline/sodic zone than in the productive soil, suggesting that the saline/sodic soil had a high potential for denitrification. These findings suggest N 2 O-N emissions could be reduced by not applying N to saline/sodic zones.

Weed presence early in the life cycle of maize (typically, from emergence through the 8 to 12 leaf growth stage) can reduce crop growth and yield and is known as the critical weed-free period (CWFP). Even if weeds are removed during or just after the CWFP, crop growth and yield often are not recoverable. We compared transcriptome responses of field-grown hybrid maize at V8 in two consecutive years among plants grown under weed-free and two weed-stressed conditions (weeds removed at V4 or present through V8) using RNAseq analysis techniques. Compared with weed-free plant responses, physiological differences at V8 were identified in all weed-stressed plants and were most often associated with altered photosynthetic processes, hormone signaling, nitrogen use and transport, and biotic stress responses. Even when weeds were removed at V4 and tissues sampled at V8, carbon: nitrogen supply imbalance, salicylic acid signals, and growth responses differed between the weed-stressed and weed-free plants. These underlying processes and a small number of developmentally important genes are potential targets for decreasing the maize response to weed pressure. Expression differences of several novel, long noncoding RNAs resulting from exposure of maize to weeds during the CWFP were also observed and could open new avenues for investigation into the function of these transcription units. K E Y W O R D Smaize, plant-plant interaction, transcriptome, weeds

Despite differences between the cover crop growth and decomposition phases, few greenhouse gas (GHG) studies have separated these phases from each other. This study's hypothesis was that a living cover crop reduces soil inorganic N concentrations and soil water, thereby reducing N 2 O emissions. We quantified the effects of a fall-planted living cereal rye (Secale cereale L.) cover crop (2017, 2018, 2019) on the following spring's soil temperature, soil water, water-filled porosity (WFP), inorganic N, and GHG (N 2 O-N and CO 2 -C) emissions and compared these measurements to bare soil. The experimental design was a randomized complete block, where years were treated as blocks. Rye was fall planted in 2017, 2018, and 2019, but mostly emerged the following spring. The GHG emissions were near-continuously measured from early spring through June. Rye biomass was 1,049, 428, and 2,647 kg ha -1 in 2018, 2019, and 2020, respectively. Compared to the bare soil, rye reduced WFP in the surface 5 cm by 29, 15, and 26% in 2018, 2019, and 2020 and reduced soil NO 3 -N in surface 30 cm by 53% in 2019 (p = .04) and 65% in 2020 (p = .07), respectively. Rye changed the N 2 O and CO 2 frequency emission signatures. It also reduced N 2 O emissions by 66% but did not influence CO 2 -C emissions during the period prior to corn (Zea mays L.) emergence (VE). After VE, rye and bare soils N 2 O emissions were similar. These results suggest that nitrous oxide (N 2 O-N) sampling protocols must account for early season impacts of the living cover.

The impact of interactions between management and climate on nitrous oxide (N2O), carbon dioxide (CO2), and ammonia (NH3) emissions are not well understood. This study quantified the effect of urea fertilizer application timing on inorganic N movement, immobilization, and the gaseous emissions of N2O‐N, CO2‐C, and NH3‐N. Urea was applied once, at two rates (0 and 224 kg ha−1) on six dates (early fall, 20 Sept. 2017; mid‐fall, 11 Oct. 2017; early winter, 1 Nov. 2017; early spring, 1 May 2018; mid‐spring, 22 May 2018; and early summer, 12 June 2018). Gaseous emissions, soil temperature, and soil moisture were measured every 4 h for 21 consecutive days following urea application. Changes in soil inorganic N contents were used to determine the amount of inorganic N remaining in the soil, nitrification, immobilization/fixation, and leaching. For all fertilizer application dates, the cumulative fertilizer derived N2O‐N emissions for the 21 days following application were <0.05% of the applied N. Fertilizer‐derived N2O‐N emission rates were higher than N2O‐N emission rates in the unfertilized soil in early fall and early summer. Even though the highest net N2O‐N emissions occurred in early spring, the application of fertilizer did not increase emissions. The highest net N2O‐N + NH3‐N emissions occurred in cool soils (early spring) in soils with water filled pore space (>60%). These findings indicate that intergovernmental panel on climate change (IPCC) default value of 1% of applied N for N2O emissions improved by considering the fertilizer application date.

Consumer demand for sustainably produced agricultural products is increasing. One approach that can be used to evaluate and compare product sustainability is to conduct a life cycle analysis (LCA). The term LCA is broadly used to describe a suite of analytical resources and standardized methods. Life cycle analyses are a transdisciplinary tool which can and are used by all professions but work best when conducted by teams with diverse skills and backgrounds. The objective of this paper is to provide a primer on LCAs for the agricultural community and for LCA practitioners unfamiliar with agronomy. Agricultural LCAs can differ greatly because agricultural products have multiple end uses, complex socioeconomic and environmental trade-offs, and can be generated using a variety of different practices, resources, and production systems. Through worldwide agricultural marketing, intricate agronomic supply chains and support systems have been developed to produce, store, and distribute agricultural products. In many situations, the production practices are not linked to the products consumers