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Relative contributions of diverse, managed ecosystems to greenhouse gases are not completely documented. This study was conducted to estimate soil surface fluxes of carbon dioxide (CO(2)), methane (CH(4)), and nitrous oxide (N(2)O) as affected by management practices and weather. Gas fluxes were measured by vented, static chambers in Drummer and Raub soil series during two growing seasons. Treatments evaluated were corn cropped continuously (CC) or in rotation with soybean (CS) and fertilized with in-season urea-ammonium nitrate (UAN) or liquid swine manure applied in the spring (SM) or fall (FM). Soybean (SC) rotated with CS and restored prairie grass (PG) were also included. The CO(2) fluxes correlated (P 8 kg ha(-1) yr(-1) in CCSM; differences were driven by pulse emissions after N fertilization in concurrence with major rainfall events. These results suggest fall manure application, corn-soybean rotation, and restoration of prairies may diminish N(2)O emissions and hence contribute to global warming mitigation.

Concern over climate ciiange has stimuiated interest in the temperature and moisture dependence of sou organic matter decomposition. In particuiar, there has been intense debate in relation to the factors that determine the temperature dependence of C mineralization. We examined temperature and moisture responses of C and N mineralization in an 85-d laboratory incubation (factorial combination of four temperatures [5, 12, 18, 25°C] and five moisture treatments [matric potential from -5 to -1200 kPa]) using three agriculturaiiy important New Zealand sous (sous with a iiistory of pasture, arabie, or vegetable cropping). Mineralization was iinearly related to gravimetric moisture content, except in the high-C pasture soil where Oj suppiy apparentiy iimited mineraiization at high (25°C) temperature-moisture combinations. Temperature responses were adequately described by a Q^Q function (Q-¡Q values for C mineralization ranged 1.9-2.8). The pooi of mineraiizabie C, estimated using a first-order kinetic modei, increased as temperature and moisture increased, whereas the rate constant did not show a consistent trend witii either temperature or moisture. Part of the C mineralized during tiie incubation was from the microbial biomass (post-incubation biomass C decreased by an average of 0.22-0.31 mg kg~^ for each 1 mg kg~^ CO2-C evolved). Microbiai biomass C (MBC) was particuiariy sensitive to temperature (post-incubation biomass C decreased 18-35% between 5-25°C).Tiie deciine in MBC between 5 and 12°C represented an average of 40% of the C mineraiization increase in tiiat temperature intervai. Between 18 and 25°C, the decline in MBC was equivalent to only 20% (on average) of tiie C mineraiized in tiiat temperature interval. High Q^Q vaiues reported in iaboratory incubations at low temperature may be partly due to mineraiization of microbiai C.Abbreviations: DOM, dissolved organic matter; MBC, microbial biomass carbon; SOM, soil organic matter. S oil organic matter (SOM) plays a key role in the global C and N cycles. Soils contain more than twice as much C as the atmosphere and three times the amount stored in living plants (Schlesinger, 1997). Key factors determining the levels of SOM are inputs of plant and animal residues and losses via decomposition. Decomposition (mineralization) of SOM is microbially mediated, with the rate of mineralization being strongly dependent on temperature and soil moisture. Stanford and his coworkers (Stanford and Smith, 1972;Stanford and Epstein, 1974;Stanford et al., 1973) advanced the concept of a potentially mineraiizabie pool of organic matter and a related mineralization rate constant to characterize the temporal pattern of N mineralization. There is wide acceptance that each soil has a fixed quantity of mineraiizabie N (and C), which can be experimentally determined using incubation assays (Campbell et al., 1993;Motavalli et al., 1994). In theory, potentially mineraiizabie C is the amount of C that will mineralize in infinite time. In practice, it is estimated by incubating soil und...

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Improving N fertilization in croplands could minimize soil emissions of nitrous oxide (N2O) and mitigate climate change. This study investigated the effects of spring vs. fall N applications of conventional vs. enhanced‐efficiency N fertilizers (EENFs) on N2O emissions and N use efficiency in spring wheat (Triticum aestivum L.) over 2.5 yr in Alberta, Canada. Fertilizers were anhydrous ammonia and urea and the EENF formulations included urease and nitrification inhibitors and a polymer coating. We measured a fertilizer N2O emission factor of 0.31 ± 0.04%. Irrespective of N fertilizer and timing options peak N2O emissions were evident following soil thawing and major rainfalls. Because most of the annual N2O emissions were associated with soil thawing, spring‐applied N emitted half the N2O of the fall‐applied N during the second study year (P < .001). Conversely, the opposite was observed for the first study year when overall N2O emissions were 36% larger for spring‐ than fall‐applied N (P = .031) as major rainfalls occurred shortly after the spring N fertilization. Nevertheless, within this first study year, EENFs significantly reduced N2O emissions (by 26% on average; P = .019), with a tendency for 11% higher grain yield across springtime EENFs than for conventional fertilizers. Concomitantly, spring‐applied N doubled the fertilizer N recovery efficiency in the same year (P = .023). The soil at the study site inherently had high N availability (NH4 and NO3) and this probably moderated the beneficial effects of EENFs on N2O emissions and grain yields. Results suggest that spring EENFs can mitigate the risk for N2O emissions while sustaining high yields even under scenarios with high availability of native soil N.

Mitigating the greenhouse gas emissions that arise durin manure is a crucial environmental challenge. We evalu effects of liquid manure timing (fall vs. spring) and nitrifi [2-chloro-6-(trichloromethyl) pyridine (nitrapyrin) vs. 3 phosphate (DMpp)] on n 2 O emissions, soil mineral n ley (Hordeum vulgare L.) productivity, and n uptake. E established in an incomplete split-plot design in Laco AB, Canada. Repeated measurements included n 2 O flu chambers, and soil ammonium (nH 4 -n) and nitrate (nO Relative to the manured soils without nIs, the use of n significantly reduced annual n 2 O emissions by 81% w with nitrapyrin in our Lacombe site; however, this diffe in the comparable spring treatments applied during the These beneficial effects were discernable in Lacombe, wetter than Edmonton, indicating the overriding role o n dynamics and fluxes. Following a 5-mo freezing wi caused at least 64% of annual n 2 O emissions from the f these intense episodic fluxes also revealed that the effic still continued during the early spring. On average, fal the n 2 O direct emission factors by about threefold com sponding spring treatments. Thus implementing liquid m nIs at the right timing has the potential opportunity to crops and simultaneously diminish global warming effect Abbreviations: CT, control treatment where the soil was disturb without soil disturbance); DM, dry matter; DMPP, 3, 4-dimethyl direct emission factors; FMD, fall-manured soil with DMPP, FMN nitrapyrin; FMW, fall-manured soil with no nitrification inhibitors; SMD, spring-manured soil with DMPP; SMN, spring-manured so spring-manured soil with no nitrification inhibitors.

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