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Figure 1. Effect of different KNO3 concentrations on A) soil N turnover and emission rates (mg N kg-1 dry soil h-1), and
B) the N2O/(N2O+N2) product ratio of denitrification in long-term limed (pH 7) and non-limed control (pH 4) soils in Exp.1. The course of C) N2O/(N2O+N2) product ratios of denitrification at N level of 15 mM KNO3 in long-term limed (pH 7) and non-limed control (pH 4) soils in Exp. 2 In Exp. 2, denitrification rates were about two fold higher in HpH than in LpH. However, denitrification rates decreased gradually in HpH, whereas in LpH, they remained almost constant during the 450 hours of the experiment. The N2O/(N2O+N2) product ratio of denitrification increased sharply with the start of anoxic period (Fig. 1B). In HpH the N2O/(N2O+N2) product ratio decreased rapidly while in LpH it remained almost constant for around 100 hours and then decreased gradually towards zero. The results illustrate that the length of an anoxic spell is a third factor affecting the N2O/(N2O+N2) product ratio of denitrification. This means that short anoxic spells will result in high N2O/(N2O+N2) product ratio even in high pH soil. In low-pH soil however, the product ratio will be high for longer periods of anoxia.
4. Conclusion The higher N2O/(N2O+N2) product ratio of denitrification in acid soil compared to limed soil with low NO3- content, may be explained by lacking demand for electron acceptor. In addition, the effect of pH on N2O/(N2O+N2) product ratio of denitrification is weakened by increasing nitrate concentration and long anoxic spells.
References Cuhel, J. and Simek, M. 2011. Proximal and distal control by pH of denitrification rate in a pasture soil. Agriculture Ecosystem and Environment. 141, 230-233.
Liu, B., Morkved, P.T., Frostegard, A. and Bakken L.R. 2010. Denitrification gene pools, transcription and kinetics of NO, N2O and N2 production as affected by soil pH. FEMS Microbiology Ecelogy 72, 407-417.
Senbayram, M., Chen, R., Budai, A., Bakken, L. and Ditert, K. 2012. N2O emission and the N2O/(N2O+N2) product ratio of denitrification as controlled by available carbon substrates and nitrate concentrations. Agriculture Ecosystem and Environment 147, 4-12.
Simek, M. and Cooper, J.E. 2002. The influence of soil pH on denitrification: progress towards the understanding of this interaction over the last 50 years. European Journal of Soil Science 53, 345-354.
Nitrogen Workshop 2012
Spatiotemporal variation in groundwater nitrate-N concentrations in two agricultural catchments Mellander, P-E.a, Melland, A.R.a, Murphy, P.N.C.a, Wall, D.a, Shortle, G.a, Jordan, P.b a Agricultural Catchments Programme, Teagasc, Johnstown Castle, Environmental Research Centre, Co Wexford, Rep.
of Ireland b School of Environmental Sciences, University of Ulster, Coleraine, N. Ireland
1. Background & Objectives In order to mitigate anthropogenic nutrient transfers to surface waters in agricultural catchments there is a need to identify and quantify the transfer pathways and their influence on nutrient delivery to streams. It is further useful to understand how those pathways may vary in time and space and in their connection to nutrient sources, and the effect of temporal changes in water recharge and land management. The Agricultural Catchments Programme (ACP) aims to provide scientific evidence needed to support Irish agriculture in meeting the requirements of the Water Framework Directive (WFD). A ‘nutrient transfer continuum’ from source, through pathways, to delivery and impact in a water body receptor is used as a framework for evaluation of the European Union Nitrates Directive regulations and the Surface and Groundwater regulations. In agricultural river catchments with permeable soils nitrogen (N) loads tend to reflect that of near stream groundwater N concentrations of different strata, during both event and baseflow conditions, and sub-surface pathways are considered to be the major N transfer pathways throughout the year. In this paper we investigate possible links between N sources, groundwater and surface water as well as the implication of spatiotemporal variation for mitigation measures.
2. Materials & Methods We present two years of N concentration data in streamwater and groundwater of different strata in two c. 10 km2 agricultural catchments with permeable soils; one with arable land overlying slate bedrock (Co. Wexford, Ireland) and the other with intensively managed grassland on sandstone (Co.
Cork, Ireland). Both catchments have two focused study sites (hill slope transects) chosen to represent the land use, soil type, geology and topography following conceptual modelling of existing data layers and geophysical surveying (including ground conductivity [EM 31 and EM 38], ground penetrating radar, 2D-resistivity and seismic refraction). Each site is equipped with three multilevel monitoring wells from which piezometric water levels are monitored and monthly water quality samples taken. In-stream N concentrations at the catchment outlet are measured in-situ on a sub-hourly basis using bankside analysers and discharge is monitored at rated non-standard flat-v weirs. Rainfall and weather parameters for estimating potential evapotranspiration are also being measured and nutrient and farm management practices are recorded at the field level.
3. Results & Discussion Belowground hydrological pathways dominated in both catchments. In the grassland/sandstone catchment, hydrological pathways were mostly within the shallow bedrock, whereas the arable/slate had a relatively quick flow within the transition zone and shallow bedrock consisting of highly permeable weathered rock overlying competent rock and, therefore, showed a quicker response to rainfall in terms of water recharge and streamflow generation. Relatively high concentrations of N were found in groundwater, attributed to leaching of surplus soil nitrate-N (Figure 1). During a large flow event (summer, 2010) 95% of the total oxidised nitrogen was delivered to the stream by belowground pathways in both catchments. The grassland/sandstone catchment had higher nitrate-N concentrations and showed more seasonal and spatial variability. The highest nitrate-N
Nitrogen Workshop 2012
concentrations were found in the shallow strata of the near-stream zone. That zone was also more stratified in the grassland/sandstone than in the arable/slate and also more stratified compared to the uplands. In one hillslope of the grassland/sandstone catchment N was buffered in the near-stream zone, but this zone was bypassed with high nitrate-N content water from the uplands via subsurface drains. Effects of pasture reseeding (including mineralization of soil N) and slurry spreading in August 2010 were observed in the groundwater N concentration of the grassland/sandstone catchment but with a delay of c. five months (Figure 1). Effects of spatial and temporal differences in recharge were also observed in the groundwater N concentration due to localised more permeable subsoils (lenses of gravel) and due to seasonal difference in rainfall and evapotranspiration.
Transport time will have an important role in determining the exposure time to biogeochemical processes that can attenuate N and the pathway will determine both the time-lag and biogeochemical processes that N is exposed to.
Figure 1. Nitrate-N concentration in groundwater of different strata in the upslope, midslope and near-stream of the grassland/sandstone catchment (left) and the arable/slate catchment (right).
Irish drinking water standards (NO3-N = 8.5 mg L-1) and MAC (NO3-N = 11.3 mg L-1) are marked with horizontal red and blue dashed lines. Vertical red line marks a reseeding and slurry spreading event in August 2010.
4. Conclusion Nutrient sources were connected to surface water via groundwater in both catchments. Land management, geology and weather were seen to influence the observed concentrations of N in groundwater, both spatially and temporarily. In selecting mitigation options it is important to understand the integrated effects on groundwater quality of spatiotemporal variability in recharge and land management. For effective characterization of nutrient transfer pathways in catchments with permeable soils we suggest including a chemical groundwater signature that represents the catchment for each geological strata.
Nitrogen Workshop 2012
Strategies to reduce nitrous oxide emissions after spread of pig slurry in no-till corn and wheat Aita, C.a, Schurman, J.a, Giacomini, S.J.a, Gonzatto, R.a, Olivo, J.a, Giacomini, D.A.a a Department of Soil Science, Federal University of Santa Maria, Santa Maria, RS, Brazil.
1. Background & Objectives It is relatively well documented in the literature that pig slurry may increase N2O emissions because it contains inorganic N, microbial available sources of carbon, and water (Rochette et al., 2004;
Chadwick et al., 2011). Additionally, the presence of straw in no-till conditions enhances availability of soluble carbon to heterotrophic decomposers that may create anoxic conditions, contributing to microbial production of N2O after slurry spreading. In the South of Brazil, almost all of pig slurry is applied under no-till conditions. Therefore, it is necessary to quantify N2O emissions in this situation and to develop strategies for its mitigation. The objective of this study is to evaluate the effect of split application of pig slurry and use of nitrification inhibitor as strategies to reduce N2O emissions in no-till corn and wheat.
2. Materials & Methods The study was conducted at the Research Farm of Soil Department, Federal University of Santa Maria, Brazil (29º43’S; 53º43’W; altitude: 105 m). The soil texture was loam consisting of 223 g clay, 379 g silt and 398 g sand kg-1 in 0-20 cm layer, respectively. The experiment was carried out under no-till conditions for one year. The treatments used for both crops i.e. corn (Zea mays L.) (planting date: 12/11/2010) and wheat (Triticum aestivium L.) (planting date: 01/06/2011) were:
without slurry (control), pig slurry fully applied before planting with and without Agrotain Plus (AP, containing 81% of the nitrification inhibitor dicyandiamide-DCD), pig slurry split (1/3 before planting and 2/3 in post emergence) with and without AP, and N-urea (1/3 before planting and 2/3 in post emergence). In pre-planting (no-split slurry application) the amounts of total N added was 168 kg ha-1 (120 kg ha-1 as N-NH4+) in corn and 152 kg ha-1 (102 kg ha-1 as N-NH4+) in wheat. In post-emergence (split application) the amounts of total N added was 109 kg ha-1 (99 kg ha-1 as NNH4+) in corn and 104 kg ha-1 (71 kg ha-1 as N-NH4+) in wheat. Randomized complete block design with four replications was used. In situ N2O fluxes were measured periodically by the static closed chamber technique. Gas samples were analyzed for N2O concentration using a gas chromatograph (Shimadzu GC-2014 Greenhouse model).
3. Results & Discussion Episodes of higher N2O emission were transient and coincided with periods of no-split (preplanting) and split (post-emergence) corn and wheat slurry application (Figure 1). Higher N2O fluxes were observed in split slurry in corn and in no-split slurry in wheat, both without nitrification inhibitor. Accumulated N2O emission was not affected by the split application of pig slurry in corn, but this strategy of slurry use significantly reduced N2O emission in wheat (Table 1). The use of dicyandiamide (DCD) with pig slurry reduced N2O emission in 14.2 % in corn and 125 % in wheat.
4. Conclusion This work showed that split application of pig slurry and the use of the nitrification inhibitor diciandyamide (DCD) are potential strategies to reduce N2O emissions in no-till corn and wheat.
References Chadwick, D., Sommer, S., Thorman, R., Fangueiro, D., Cardenas, L., Amon, B., Misselbrook, T. 2011. Manure management: Implications for greenhouse gas emissions, Animal feed Science and Technology 166-167, 514-531.
Rochette, P., Angers, D.A., Chantigny, M.H., Bertrand, N., Côté, D. 2004. Carbon dioxide and nitrous oxide emissions following fall and spring applications of pig slurry to an agricultural soil, Soil Science Society of America Journal 68, 1410–1420
Nitrogen Workshop 2012
Study of the key factors which influence N2O and CO2 emissions in a fertigation cropping system under Mediterranean climate Ábalos, D.a, Sánchez-Martín, L.a, Garcia-Torres, L.a, Téllez, A.a, García-Marco, S.a, Sanz-Cobeña, A.a, Vallejo, A.a a ETSI Agrónomos, Technical University of Madrid, Ciudad Universitaria, 28040 Madrid, Spain
1. Background & Objectives For a summer crop in the Mediterranean climate, irrigation management and type of fertilizer are two of the most important factors influencing emissions of greenhouse gases (GHG) from irrigated agricultural soils. Localized irrigation techniques such as drip irrigation (DI) influence soil moisture, producing wet and dry areas and, therefore, influence the processes responsible for the production and consumption of GHG (Sanchez-Martin et al., 2008). Irrigation frequency, together with high evapotranspiration during summer season, influence soil microbial activity and, therefore, emissions of GHG. A targeted combination of N fertilizer and irrigation frequency could help decrease GHG emissions, leading to a more sustainable cropping system. A field experiment was carried out in summer 2011 under a melon crop in order to evaluate the emissions of two of the most important GHG, nitrous oxide (N2O) and carbon dioxide (CO2), in relation to irrigation frequency and type of fertilizer.
2. Materials & Methods A field experiment was carried out at ‘El Encín’ field station in Madrid (40º 32’N; 3º 17’ W) on a melon crop. Eighteen plots (20 m2) were selected and arranged in a randomized complete block design with 3 N treatments x 2 irrigation frequencies x 3 repetitions. Nine of them were irrigated 1 day per week (low frequency; LF) and the other nine were irrigated 7 days per week (high frequency; HF). N treatments were applied under both irrigation frequencies: calcium nitrate (NLF;
NHF), urea (ULF; UHF) and control plots without any N application (CLF; CHF). N fertilisers were applied weekly from 19th July to 19th September by fertigation, at a total rate of 125 kg N ha-1.