Nitrous oxide from incorporated crop residues and green manures

A series of field and laboratory experiments were undertaken to examine the effects of incorporation of plant material on emissions of N₂0 from agricultural soils. The overall aim was to increase understanding of that part of the agricultural N cycle, associated with the release of N after incorporation of crop residues and green manures into soil, and subsequent N₂0 emissions to the atmosphere. N20 emissions from growing crops and following addition of various residues and green manures to soil were measured and compared. The effects of crop type, fertiliser application, cultivation techniques, soil type, and climatic conditions, and also of the addition of high C substrate in the form of paper waste, on these emissions were investigated.Emissions of N₂0 were increased after cultivation of soil, attributed to increased accessibility of organic matter to soil microbes, and improved gaseous diffusion. Emissions were higher following incorporation of plant material than emissions from bare soil. Generally, fluxes were increased within a few hours or days after cultivation and/or incorporation, but the effect was short-lived. Most of the N₂0 was emitted during the first 2 weeks. The magnitude and timing of N₂0 released within this period was highly dependent on temperature and rainfall following incorporation, and the cultivation technique employed.The C:N ratio of the incorporated plant material had a considerable effect on rates of decomposition, and on subsequent N₂0 production during nitrification and denitrification. Higher emissions were typically measured after incorporation of material with a low C:N ratio, such as legumes, than when material with higher ratios, such as cereal straw, was involved. When material with a high C:N ratio was added, N was immobilised. Nevertheless, the presence of high C:N paper waste increased N₂0 emissions from incorporated vegetable crop residues. This was attributed to the creation of more anaerobic sites in the soil.Emissions of N₂0 increased within a few days of applying mineral N fertiliser to spring-sown cereal crops. Again, these fluxes were short-lived. Use of 15N-labelling in this experiment showed that approximately 50% of crop N at harvest was derived from applied fertiliser. In other experiments, the presence of a growing crop, particularly a legume, increased emissions, compared with those measured from bare soil

Substrate Induced Denitrification over or under Estimates Shifts in Soil N2/N2O Ratios

Funding: Funding was provided by the Biotechnology and Biological Sciences Research Council, BBSRC UK (http://www.bbsrc.ac.uk). Grant number BB/H013431/1. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Peer reviewedPublisher PD

Plant exudates improve the mechanical conditions for root penetration through compacted soils

ACKNOWLEDGEMENTS Funding for this project was provided by Tertiary Education Trust Funds (TETFund) and Ambrose Alli University. We wish to thank Annette Raffan for technical support. M. Naveed is funded by the Biotechnology and Biological Sciences Research Council (BBSRC) project ‘Rhizosphere by Design’ (BB/L026058/1). Open access via Springer Compact AgreementPeer reviewedPublisher PD

Inorganic nitrogen and glucose additions alter the short-term formation efficiency of mineral associated organic matter carbon

Carbon within mineral associated organic matter (MAOM) is an important persistent form of soil organic carbon (SOC). However, processes driving the retention of new labile C in MAOM are not fully understood. We investigated the effects of glucose and ammonium nitrate (AN) addition on the short-term (72 h) retention of applied 13C-glucose within MAOM. We found an interactive effect of AN addition with the glucose addition rate. Higher rates of glucose addition resulted in proportionally less glucose-C retained, indicating lower MAOM-C formation efficiency. Addition of AN only altered the proportional retention of glucose where glucose was applied at the lowest rate. In this instance glucose-13C recovery increased with AN addition. However, after 72 h there was no treatment difference in total MAOM-C, indicating that any changes in formation efficiency as a result of AN and glucose additions, did not result in differences in total MAOM-C in the short-term. Whether and how this affects the medium and longer-term dynamics of MAOM-C requires further investigation

Soil nitrate reducing processes drivers, mechanisms for spatial variation, and significance for nitrous oxide production

The microbial processes of denitrification and dissimilatory nitrate reduction to ammonium (DNRA) are two important nitrate reducing mechanisms in soil, which are responsible for the loss of nitrate (NO− 3 ) and production of the potent greenhouse gas, nitrous oxide (N2O). A number of factors are known to control these processes, including O2 concentrations and moisture content, N, C, pH, and the size and community structure of nitrate reducing organisms responsible for the processes. There is an increasing understanding associated with many of these controls on flux through the nitrogen cycle in soil systems. However, there remains uncertainty about how the nitrate reducing communities are linked to environmental variables and the flux of products from these processes. The high spatial variability of environmental controls and microbial communities across small sub centimeter areas of soil may prove to be critical in determining why an understanding of the links between biotic and abiotic controls has proved elusive. This spatial effect is often overlooked as a driver of nitrate reducing processes. An increased knowledge of the effects of spatial heterogeneity in soil on nitrate reduction processes will be fundamental in understanding the drivers, location, and potential for N2O production from soils

Resilience of soil functions to transient and persistent stresses is improved more by residue incorporation than the activity of earthworms

The development of soil sustainability is linked to the improved management of soil biota, such as earthworms, and crop residues to improve soil physical structure, enhance microbial activities, and increase nutrient cycling. This study examined the impacts of maize residue (65.8 C/N ratio, dry biomass 0.75 kg m-2) incorporation and earthworms (70 g Metaphire guillelmi m-2) on the resistance and resilience of soil C and N cycling to experimentally applied stresses. Field treatments were maize residue incorporation, maize residue incorporation with earthworm addition, and an unamended control. Resistance and resilience of C mineralization, ammonia oxidation, and potential denitrification were investigated over 28 days following a persistent stress of Cu (1 mg Cu soil g-1) or a transient heat stress (50 ℃ for 16 hours). The results indicated that C mineralization was more resistant and resilient than ammonia oxidation and denitrification to either a persistent Cu or a transient heat stress. The application of maize residues significantly increased soil microbial biomass, C mineralization, ammonia oxidation and potential denitrification compared with the unamended control. Maize residues significantly improved the resistance and resilience of N processes to Cu and heat stress. The presence of earthworms significantly increased potential denitrification but had limited positive effect on functional resistance and resilience. This study suggested crop residue incorporation would strongly increase soil functional resistance and resilience to persistent and transient stresses, and thus could be a useful agricultural practice to improve soil ecosystem sustainability

Do soil depth and plant community composition interact to modify the resistance and resilience of grassland ecosystem functioning to drought?

While the effect of drought on plant communities and their associated ecosystem functions is well studied, little research has considered how responses are modified by soil depth and depth heterogeneity. We conducted a mesocosm study comprising shallow and deep soils, and variable and uniform soil depths, and two levels of plant community composition, and exposed them to a simulated drought to test for interactive effects of these treatments on the resilience of carbon dioxide fluxes, plant functional traits, and soil chemical properties. We tested the hypotheses that: 1) shallow and variable depth soils lead to increased resistance and resilience of ecosystem functions to drought due to more exploitative plant trait strategies; 2) plant communities associated with intensively managed high fertility soils, will have more exploitative root traits than extensively managed, lower fertility plant communities. These traits will be associated with higher resistance and resilience to drought and may interact with soil depth and depth heterogeneity to amplify the effects on ecosystem functions.Our results showed that while there were strong soil depth/heterogeneity effects on plant driven carbon fluxes, it did not affect resistance or resilience to drought, and there were no treatment effects on plant available carbon or nitrogen. We did observe a significant increase in exploitative root traits in shallow and variable soils relative to deep and uniform, which may have resulted in a compensation effect which led to the similar drought responses.Plant community compositions representative of intensive management were more drought resilient than more diverse “extensive” communities irrespective of soil depth or soil depth heterogeneity. In intensively managed plant communities, root traits were more representative of exploitative strategies. Taken together our results suggest that reorganisation of root traits in response to soil depth could buffer drought effects on ecosystem functions.<br/

Complex controls on nitrous oxide flux across a large elevation gradient in the tropical Peruvian Andes

Acknowledgements The authors would like to acknowledge the agencies that funded this research; the UK Natural Environment Research Council (NERC; joint grant references NE/H006583, NE/H007849 and NE/H006753). Patrick Meir was supported by an Australian Research Council Fellowship (FT110100457). Javie Eduardo Silva Espejo, Walter Huaraca Huasco and the ABIDA NGO provided critical fieldwork and logistical support. Angus Calder (University of St.Andrews) and Vicky Munro (University of Aberdeen) provided invaluable laboratory support. Thanks to Adrian Tejedor from the Amazon Conservation Association, who provided assistance with site access and site selection at Hacienda Villa Carmen. This publication is a contribution from the Scottish Alliance for Geoscience, Environment and Society (http://www.sages.ac.uk).Peer reviewedPublisher PD