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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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In late autumn, after turning under the ley, amounts of soil mineral N to 90 cm depth was significantly highest after pure clover (mean 5.6 g N m-2), followed by the mixed ley (27 g N m-2) and least after pure grass ley (14 g N m-2), and higher after intact leys (38 g N m-2) than after mulched leys (27 g N m-2). However, soil mineral N in spring was similar after pure clover and mixed leys and after intact and mulched stands. Nitrogen supply from the ley to the following oat crop resulted in similar and approx. 20% higher yields (corresponding to an additional 1000 kg grain ha-1) in the pure clover and mixed ley treatments compared with the pure grass treatment. Nitrogen use efficiency expressed as N in oat grain and straw at harvest in relation to total fixed N2 was on average 58% for the intact mixed ley and about 30% for the mulched leys and the intact pure clover ley. However, the differences were not significantly different. Overall, the high soil mineral N concentration in autumn after pure clover compared with mixed ley, and the subsequent risk for substantial N losses, did not convey any harvest benefit. Also, the larger amount of fixed N2 obtained in the mulched than in the intact leys had no significant effect on the cereal yield during the first year after ley incorporation.

4. Conclusion The results indicate that N flows are larger in mulched and harvested green manure leys than in intact leys. The amount of fixed N2 below-ground was not affected by the cutting regime, but the below-ground N made up a larger proportion of the fixed N2 in the intact treatments than in the cut treatments. This shows that the cutting strategy should be taken into consideration when estimating total nitrogen fixation in green manure leys. To minimize the potential negative environmental effects, we recommend that green manure leys should be harvested rather than mulched, and mixed stands including grasses should be used rather than pure legume stands.

References Dahlin A.S., Stenberg M. and Marstorp H. 2011. Mulch N recycling in green manure leys under Scandinavian conditions. Nutrient Cycling in Agroecosystems 91, 119-129.

Dahlin A.S. and Stenberg M. 2010. Translocation of N from red clover to perennial ryegrass in mixed stands under different cutting strategies. European Journal of Agronomy 33, 149-156.

Dahlin A,S. and Stenberg M. 2010. Cutting affects the amounts and allocation of symbiotically fixed N in green manure leys. Plant and Soil 331, 401-412.

Heuwinkel, H., Guts, R., Schmid, X. and Halter, U. 2005. Does N-cycling impair the N2 fixing activity of mulched legumes-grass in the Field? In Sebastia T, Helgadóttir A (eds) Adaptation and Management of Forage Legumes-Strategies for Improved reliability in mixed sward. Proceedings of the 1st COST 852 Workshop, Ystad, Sweden 20-23 Sept. 2004, pp. 141-144.

Høgh-Jensen, H. and Schjørring, J.K., 2000. Below-ground nitrogen transfer between different grassland species:

direct quantification by 15Nleaf feeding compared with indirect dilution of soil 15N. Plant and Soil 227, 171-183.

Nitrogen Workshop 2012

Long-term effect of a nitrification inhibitor on N2O fluxes from a loamy soil Ruser, R.a, Pfab, H.a, Schulz, R.a, Palmer, I.b, Fiedler, S.b, Buegger, F.c, Müller, T.a a Institute of Crop Science, Fertilisation and Soil Matter Dynamics (340i), Universität Hohenheim, Stuttgart, Germany b Institute of Soil Science and Land Evaluation (310), Universität Hohenheim, Stuttgart, Germany c Institute of Soil Ecology, Helmholtz Zentrum München, German Research Center for Environmental Health, Neuherberg, Germany

1. Background & Objectives Nitrification inhibitors (NIs) originally were introduced in agriculture to reduce nitrate leaching after fertilizer application. All commercial available NIs inhibit the enzymatic transformation of ammonium to hydroxylamine and thus delay nitrate production from NH4+-N. Kaiser and Ruser (2000) reported that about 50% of the annual N2O emission from German study sites occurred in winter during freezing/thawing cycles. Therefore, annual data sets are a prerequisite for a reliable evaluation of the atmospheric impact of management measures. Akiyama et al. (2010) summarized available data on N2O fluxes after NI application. Among the 85 data sets evaluated, there were only 12 annual data sets from which 11 sets were measured under conditions without distinctive freeze/thaw changes. To our knowledge, there are currently no annual N2O data sets for 3,4dimethylepyrazole phosphate (DMPP) which is the most common NI in German agricultural practice. The aim of the study was to test the effect DMPP on the annual N2O mitigation potential.

2. Materials & Methods The study was conducted over two experimental years at a research farm of the University of Hohenheim, south of Stuttgart. The long-term rainfall at the study site is 686 mm a-1 and the mean air temperature 8.8°C. A complete randomised block experiment with four replicates was established on a loamy Haplic Luvisol derived from loess. In each of the two years, lettuce was planted followed by cauliflower. Before the beginning of the experiment green rye was grown as a catch crop. All treatments received the same amount of N-fertiliser (150 and 286 kg mineral N ha-1 for lettuce and cauliflower, respectively) as ammonium nitrate sulphate (ASN). As NI we tested 3,4-dimethylepyrazole phosphate (DMPP). The NI is granulated with ASN commercially available as “ENTEC 26®” The fertiliser in the conventional ‘control’ treatment (-NI) and in the treatment with NI (+NI) was applied broadcast. Trace gas flux rates were measured, at least once a week, using the closed chamber method. Chamber design and calculation of the N2O and CO2 flux rates with a linear regression approach are described in detail by Flessa et al. (1995). Simultaneously to the trace gas sampling soil samples were taken from the Ap-horizon and analysed for soil moisture and mineral N.

3. Results & Discussion The cumulative N2O emissions varied between 2.8 kg N2O-N (+NI, second year) and 8.8 kg N2O-N ha-1 a-1 (-NI, first year) (Table 1). The emissions in the first year were nearly twice as high as in the second year. The reason for the higher emissions in the first year might be the incorporation of green rye immediately before planting and fertilisation. The turn-over of this material led to an additional O2 consumption favouring denitrification. As a result, the highest N2O flux rates of the whole experiment occurred in this period (not shown). No catch crop was sown in autumn of the first year. In accordance with the literature summarised by Akiyama et al. (2010) the addition of the NI strongly reduced N2O emissions during the cropping season. Despite big differences between the two experimental years the NI reduced the annual N2O emissions as compared to the –NI treatment by at least 40%. As mentioned by Akiyama et al. (2010) the lower N2O emissions after NI

–  –  –

Surprisingly, the N2O emissions in the +NI treatment were also lower in the winter season. The period of distinctive lower N2O fluxes during the winter season was more than 15 weeks after the addition of the NI. At this time the active component of DMPP must have been degraded. As reported by Zerulla et al. (2001) DMPP is decomposed within approximately six weeks (at 20°C).

In the period of lower N2O fluxes form the +NI treatment in winter there were no significant differences between the mineral N contents of the soil, neither in the NH4+- nor in the NO3-fraction. Therefore, the reason for this phenomenon remains speculative. However, as compared to the –NI treatment, a lower microbial CO2 release in the +NI treatment indicates a reduced heterotrophic activity or probably a reduction of the heterotrophic microbial biomass. Incubation studies also showed, at least on the short-term, a decreased CO2 release after the addition of DMPP (Kapoor, unpublished data). Weiske et al. (2001) also reported a reduction of the CO2 flux rates after the addition of DMPP. Without reference to the reason for the lower CO2 fluxes, it seems that the reduction of the N2O emission in the winter period was a result of a decreased N2O production during denitrification since nitrification is CO2 autotrophic.

4. Conclusion This study highlights that the addition of NIs to an NH4+ rich fertiliser has a high potential to reduce N2O emission from agricultural soils. We proofed this potential for DMPP on an annual basis.

However, further investigations on the observed effect of the NI in the winter period are necessary.

References Akiyama, H., Yan, X. and Yagi, K. 2010. Evaluation of effectiveness of enhanced-efficiency fertilizers as mitigation options for N2O and NO emissions from agricultural soils: Meta-analysis. Global Change Biology 16, 1837-1846.

Flessa, H., Dörsch, P., Beese, F. 1995. Seasonal variation of N2O and CH4 fluxes in differently managed arable soils in southern Germany. Journal of Geophysical Research 100, 115-124.

Kaiser, E. A. and Ruser, R., 2000. Nitrous oxide emissions from arable soils in Germany - An evaluation of six longterm field experiments. Journal of Plant Nutrion and Soil Science 163, 249-260.

Weiske, A., Benckiser, G. and Ottow, J.C.G. 2001. Effect of the new nitrification inhibitor DMPP in comparison to DCD on nitrous oxide (N2O) emissions and methane (CH4) oxidation during 3 years of repeated applications in field experiments. Nutrient Cycling in Agroecosystems 60, 57-64.

Zerulla, W., Barth, T., Dressel, J., Erhardt, K., Horchler von Locquenghien, K., Pasda, G., Rädle, M. and Wissemeier, A. 2001. 3,4-Dimethylpyrazole phosphate (DMPP) - A new nitrification inhibitor for agriculture and horticulture. An introduction. Biology and Fertility of Soils 34, 79-84.

Nitrogen Workshop 2012

Maize stover incorporation increased N2O emissions twofold during a barley crop Ábalos, D.1, Sanz-Cobeña, A.1, Sánchez-Martín, L.1, Téllez, A.1, García-Marco, S.1, Vallejo, A.1 ETSI Agrónomos, Technical University of Madrid, Ciudad Universitaria, 28040 Madrid, Spain

1. Background & Objectives Agricultural soils in semiarid Mediterranean areas are characterized by low organic matter contents, featuring small fertility levels (Garcia-Gil et al., 2000). Application of crop residues and/or manures as amendments is a cost-effective and sustainable alternative to overcome this problem. However, these management practices may induce important changes in the N2O emissions from these agroecosystems (Huang et al., 2004; Vallejo et al., 2006). The objective of this study was to evaluate the effect of applying maize residues and fertilizer inputs (organic and/or mineral), combined or alone, on the N2O emissions under field conditions.

2. Materials & Methods A set of plots was established in a field site which had been sown with barley. The experimental design was a randomized complete block design with three blocks and two factors: crop residue management practices (remove (-R) or retain (+R)), and fertilizer type (control without N-fertilizer application (C), pig slurry + urea (PS+U), and urea (U)). Before sowing (November) 50 kg N ha-1 were applied as urea or pig slurry depending on the treatment. The remaining 100 kg N ha-1 were applied as urea for all fertilized treatments, as a top-dressing (March). Gaseous emissions were measured using the chamber technique (Roelle et al., 1999). Denitrification capacity was measured according to the technique described by Yeomans et al. (1992) but without added C in order to evaluate if the C of crop residues and/or the organic fertilizer had a significant effect over the N2O emissions. Dissolved Organic Carbon (DOC) was determined as described by Mulvaney et al.

(1997). Soil NO3- and NH4+ were colorimetrically analyzed. Differences between treatments in the cumulative emissions were analysed using analysis of variance (ANOVA, P 0.05).

3. Results & Discussion The incorporation of maize straw significantly increased the N2O emissions during the experimental period by c. 105%. This effect was more pronounced after the top-dressing fertilization. Then, the emissions from the U and PS+U plots amended with crop residues were 138 and 90% higher, respectively, than that for the same fertilizer treatments without residue incorporation. These higher emissions were most likely due to a higher denitrification capacity stimulated by the C substrate added with the maize straw (Figure 1). The partial substitution of urea by pig slurry was a mitigation strategy to reduce N2O emissions, under the specific soil conditions in which the experiments were carried out. The most likely mechanism by which pig slurry reduced N2O emissions was by significantly reducing the N2O/N2 ratio (Dittert et al. 2005).

–  –  –

4. Conclusion This study underlines the key role of C added with maize stover residues in the emissions of N2O from soils with a low organic C content under rainfed conditions. The incorporation of crop residues increased the N2O emissions. Based in our results, its addition can’t be regarded as an improved management practice. In this type of soils pig slurry should be recommended instead of urea.

References Dittert, K., Lampe, C., Gasche, R., Butterbach-Bahl, K., Wachendorf, M., Papen, H., Sattelmacher, B. and Taube, F,

2005. Short-term effects of single or combined application of mineral N fertilizer and cattle slurry on the fluxes of radiatively active trace gases from grassland soil. Soil Biology and Biochemistry 37, 1665-1674.

Garcia-Gil, J.C., Plaza, C., Soler-Rovira, P. and Polo, A. 2000. Long-term effects of municipal solid waste compost application on soil enzyme activities and microbial biomass. Soil Biology & Biochemistry 32, 1907-1913.

Huang, Y., Zou, J., Zheng, X., Wang, Y. and Xu, X. 2004. Nitrous oxide emissions as influenced by amendment of plant residues with different C:N ratios. Soil Biology & Biochemistry 36, 973-981.

Mulvaney, R.L., Khan, S.A. and Mulvaney, C.S. 1997. Nitrogen fertilizers promote denitrification. Biology and Fertility of Soils 24, 211-220.

Roelle, P., Aneja, V. P., O`Connor, J., Robarge, W., Kim, D. and Levine., J. S. 1999. Measurement of nitrogen oxide emissions from an agricultural soil with a dynamic chamber system. Journal of Geophysical Research 104, 1609-1619.

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