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«International 17 Workshop th Nitrogen The was jointly organised by Teagasc and AFBI Printed by Print Depot Suggested citation Authors, 2012. Title ...»

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Based on the response of the tuber N yield it could be derived that for the pre plant application the NFRV of the liquid fractions was 78-81% for the clay soil location and 78-86% for the sandy soil location (Table 2). In order to assess whether ammonia volatilisation may have played caused the lower NFRV compared to CAN, in 2010 we also applied an acidified liquid fraction. For the clay soil no differences with the not acidified liquid fraction were found but on the sandy soil NFRV was significantly increased indicating that ammonia losses may have affected NFRV. As fertilisation with other nutrients than nitrogen was kept at the same level for all treatments this could not explain the observed differences. When applied at the start of tuber set, large differences in NFRV were observed between years. In 2009 NFRV was 0.40-0.44 while in 2010 values were 1.04-1.12. It must be emphasized that for the post plant application the calculated NFRV was based on one N rate while for the pre plant application the NFRV was based on 3 N rates. This makes it more difficult to assess the NFRV for the post plant application. The NFRV of the solid fraction was 32-34% on the clay soil and 34-55% on the sandy soil. Based on the composition of the solid fraction a value of about 60% was expected. As a substantial part of the total N is present in the form of ammonium (45-60%), ammonia volatilisation may have played a role. Although the solid fraction was incorporated in the soil this done quite superficially, so, part of the N may have been lost due to ammonia losses.

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4. Conclusion The results show that the NFRV of pre plant application of RO liquid fractions are lower than 100% ranging from 78-86%. No significant differences between soil types were observed.

References Van Geel, W.C.A., Van Dijk, W. and Van den Berg, W. 2011. Stikstofwerking van mineralenconcentraten bij aardappelen. Verslag van veldonderzoek in 2009 en 2010. Applied Plant Research, Lelystad, report 3250131600, pp.


Velthof, G.L. 2011. Synthesis of the research within the framework of the Mineral Concentrates Pilot. Alterra, Wageningen, report 224, pp. 72.

Nitrogen Workshop 2012

N2O and N2 production, and quantification of denitrifying populations, in various aquifer systems Barrett, M.a, Jahangir, M.M.R.b, c, Richards, K.G.b, O’Flaherty, V.a a Microbial Ecology Laboratory, Microbiology, School of Natural Sciences & Ryan Institute, National University of Ireland Galway, University Road, Galway, Ireland b Teagasc, Johnstown Castle, Environmental Research Centre, Co Wexford, Ireland c Department of Civil, Structural & Environmental Engineering, Trinity College Dublin, Ireland

1. Background & Objectives The rate of transport of nitrates to underlying groundwater systems is determined by soil type, porosity and water content (Stark and Richards, 2008). The study of microbial populations in groundwater is further complicated by the inadvertent transport to groundwater of soil microbes from the overlying soils and the continuous natural flow through aquifers. This study examined the relationship between the abundance and activity of bacterial denitrifiers in groundwater at four sites, differing with respect to overlaying land management. Groundwater was sourced from 36 multilevel piezometers, which were installed to target different groundwater zones: sub-soil, sub-soil to bedrock interface and bedrock (Jahangir et al., 2011). The gene copy concentrations (GCC) of bacterial 16S rRNA and the denitrifying functional genes, nirK, nirS, and nosZ, were determined using quantitative polymerase chain reaction assays.

2. Materials & Methods Piezometers were installed in 3 seperate zones: 1. subsoil (c. 5 m below ground level [bgl]) 2.

subsoil-bedrock interface (c.10 m bgl) and bedrock (c.20 m bgl) in three grazed grasslands (Solohead [SH], Johnstown Castle [JC] and Dairygold [DG]) and under spring barley (Oakpark [OP]). In Dairygold [DG] only bedrock was investigated at c. 40 m bgl. Dissolved N2 and Ar was measured using MIMS, and data was used to estimate excess N2 (Jahangir et al., 2011). Three seperate replicate 5 L samples were taken from each pizometer. Samples for DNA extraction were filtered through 0.2 ųm nitrocellulose membrane filters (Whatman International Ltd., England) using a vacuum pump (WELCH® vacuum pumps, Gardner Denver). The DNA extraction protocol used was as described previously (Barrett,2011). Standard curves for absolute quantifications of bacterial 16S rRNA gene (bac) and three denitrification genes (nirS, nirK and nosZ) were calculated using the corresponding standard strains and primer/probe sets (Barrett, 2011). Real-time PCR quantification was performed using a Light Cycler 480 (Roche, Mannheim, Germany) in duplicate.

Bacterial and archaeal 16S rRNA genes were analyzed using the LightCycler 480 Taqman hydrolysis probe Master kit (Roche), and the corresponding primer/probe sets and LightCycler 480 Probe Master kit (Roche), as described previously (Barrett, 2011).

3. Results & Discussion The nirK, nirS, nirT (nirK + nirS = nirT) and nosZ GCCs varied significantly? between sites, for example OP and DG experimental sites, while some variations were also observed between piezometers within sites (Figure 1). Importantly, however, and at each of the sites, nosZ GCCs correlated significantly with the presence and quantity of N2 (P 0.0001). No significant correlation was recorded between the nirK or nirS GCCs and N2O measurements (p=0.2646).

Groundwater bacterial 16S rRNA (Bac) concentrations across the four sites ranged 103-104 for all piezometers.

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Figure 1. Mean groundwater nirK, nirS, nosZ and bacterial 16S rRNA GCC L-1 filtered at (OP I:a) spring barley, (Depth – A & B=5 m) (Depth – C & D=10 m); (Depth – E=20 m) (II:a) DG grazed clover ryegrass grassland.

A significant depth by GCC interaction (p=0.0012) was observed with GCCs for the various denitrifier genes being similar across comparable piezometer depths (c. 102 - 103 - 104). Piezometer depth was significantly correlated (p=0.0256) with nirS GCC but no significant correlations were observed with nirK, nirT or nosZ (p=0.05). A significant temporal correlation was noted between nirS and piezometer depth (p=0.0256), but not between nirK and piezometer depth (p=0.9797).

Mean N2O:(N2O + N2) ratios decreased with aquifer depth (0.05 in subsoil to 0.01 in bedrock) indicating that N2O reduction to N2 occurred as groundwater moved vertically. Excess N2 was positively correlated with DOC (r=0.73) and water table depth (r=0.330), and negatively correlated with DO (r=0.70) and Ksat (r=0.47). Groundwater Nir abundance was positively correlated to N2O production (P 0.0001).

4. Conclusion The positive correlation between groundwater nosZ abundance and excess N2 concentrations indicated that determination of nosZ abundance could be used as a potential indicator of complete groundwater denitrification. Variations in the abundance of nirK and nirS- carrying microbes could be linked with land management practices thus determining a direct impact of land use on groundwater denitrifer abundance.

5. References Barrett, M. 2011. Investigating the occurance and activity of denitrifying microbial communities with relation to subsoil and groundwater denitrification capacity. PhD thesis.

Jahangir, M.M.R. 2011. Denitrification in subsoils and groundwater in Ireland. PhD thesis, School of Engineering, The University of Dublin, Trinity College, Ireland.

Stark, C.H and Richards, K.G 2008. The continuing challenge of agricultural nitrogen loss to the environment in the context of global change and advancing research. Dynamic Soil, Dynamic Plan Volume 2, 1-12.

Nitrogen Workshop 2012

N2O emission from a maize cropping system influenced by replacing fallow with cover crops and its subsequent incorporation into the soil.

García-Marco, S.a, Sanz-Cobeña, A.a, Gabriel, J.L.b, Almendros, P.a, Quemada, M.b and Vallejo, A.a a Dpto. Química y Análisis Agrícola, ETSI Agrónomos, Technical University of Madrid, Ciudad Universitaria, 28040 Madrid, Spain b Dpto. Producción Vegetal: Fitotecnia, ETSI Agrónomos, Technical University of Madrid, Ciudad Universitaria, 28040 Madrid, Spain

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4. Conclusion This study underlines the role of the use of barley and rape cover crops in intercropping periods as a N2O abatement strategy. In contrast, the incorporation of barley and rape residues increased these emissions. Based on these results, its addition cannot be regarded as a good mitigation strategy under the conditions of the experiment.

References Gabriel, J.L. and Quemada, M. 2011. Replacing bare fallow with cover crops in a maize cropping system: Yield, N uptake and fertiliser fate. European Journal of Agronomy 34, 133-143.

Eichner, M.J. 1990. Nitrous oxide emissions from fertilized soils: summary of available data. Journal of Environmental Quality 19, 272-280.

Huang, Y. et al., 2004. Nitrous oxide emissions as influenced by amendment of plant residues with different C:N ratios.

Soil Biology & Biochemistry 36, 973-981.

Roelle, P. et al., 1999. Measurement of nitrogen oxide emissions from an agricultural soil with a dynamic chamber system. Journal of Geophysical Research 104, 1609-1619.

Nitrogen Workshop 2012 Nitrate leaching after cattle slurry application to ley in autumn Delin, S.a, Stenberg, M. a, Engström, L.a a Department of Soil and Environment, Swedish University of Agricultural Sciences, Skara, Sweden

1. Background & Objectives The nitrate directive (EEC, 1991) has led to new restrictions for manure application within nitrate vulnerable zones. In Sweden this means that slurry application to growing leys in autumn is not allowed after 31st October, based on the assumption that with an earlier application, nitrogen is more utilisable by the grass. There is however little scientific evidence that the risk for nitrate leaching is higher when slurry is applied in November than earlier in autumn. The objective with this study was to compare leaching effects between slurry application to ley in early autumn, late autumn and spring.

2. Materials & Methods Nitrate leaching was measured after application of 30-45 tonnes ha-1 (50-60 kg NH4 N ha-1) of cattle slurry in early autumn (September), late autumn (November) or spring (April) to first- and second year forage grass and clover ley on a sandy loam soil in Sweden. One ley was established in 2009 and the other in 2010 with one two-year experiment in each ley during 2009-2011 and 2010-2012 respectively. Each experiment had four treatments (three manure treatments and one unmanured control) randomized into seven blocks. Yield was measured in three harvests each year after manure application. Soil water was sampled with ceramic suction cups (Djurhuus, 1990) installed in triplicate at 80 cm depth in each plot. Sampling was carried out bi-weekly during periods with water runoff, from the time of the earliest fertilisation until December the second year of harvesting. The sampled water was analyzed for nitrate (NO3-N), and nitrate leaching is determined from NO3-N concentrations in soil water and discharge measured at a nearby measuring station during the sampling period, accounting for both direct and residual effects. Soil samples (0-60 cm depth) were taken at the end of autumn (December) for determination of NH4-N and NO3-N. Subsamples of 30 g were extracted with 100 ml 2 M KCl extract. Just before late manure application and in early spring in the winter 2009/2010 the plants were sampled by cutting plants at the soil surface in four

0.25 m2 areas within each plot. The plant samples were dried at 60°C, weighed and analysed for total nitrogen content. Treatment effects were tested statistically by variance analysis.

3. Results & Discussion Soil mineral nitrogen (NO3-N + NH4-N) levels in December 2009 were elevated around 6 kg N ha-1 in autumn-manured treatments compared to the other treatments. Aboveground plant nitrogen was at this time about 40 kg N ha-1 after early application compared to around 25 kg N ha-1 in the other treatments. In April, aboveground plant nitrogen was about 10 and 5 kg N ha-1 higher in the early and late autumn-manured treatments, respectively, than in unmanured treatments. Nitrate leaching during September-August this year tended to be higher in the treatment with late autumn application, but differences were not statistically significant (Figure 1).

Soil mineral nitrogen levels in December 2010 were elevated by around 15 kg N ha-1 in early autumn-manured treatment and 30-40 kg N ha-1 in late autumn-manured treatment. Nitrate leaching during October-August this year was significantly higher from autumn manured treatment than from the other two treatments in both the first and second year ley, but there were no significant difference between early and late autumn application (Figure 1).

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Figure 1. Nitrate leaching from ley (error bars with standard error) September–August.

Total dry matter yields did not differ significantly between treatments in 2010, but in the spring manured treatment yield was a bit lower from the first cut, which was compensated by higher yield than in other treatments in the second cut. This indicates that some of the nitrogen from springapplied slurry came too late for the first harvest, but could be utilized in the next. In 2011, spring manured treatments yielded a bit more (4500 kg ha-1 compared to 4000 kg ha-1) than the other treatments, probably due to a higher NH4-N content (90 compared to 60 kg NH4-N ha-1) in manure at this application date. The intention was to apply 50 kg NH4-N ha-1 at all dates, but this was exceeded due to underestimation of ammonium concentration in slurry at the time of application in autumn 2010, and especially in spring 2011.

The higher and significant effects from autumn application on nitrate leaching during the second year may be due to the higher rate of slurry applied or to larger drainage runoff during winter.

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