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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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IPCC, 2006. 2006 IPCC Guidelines for National Greenhouse Gas Inventories. Prepared by the National Greenhouse Inventories Programme, Eggleston H.S., Buendia L., Mika K., Ngara T. And Tanabe K. (eds), Published: IGES, Japan.

de Klein C.A.M. and van Logtestijn R.S.P. 1996. Denitrification in grassland soils in Netherlands in relation to irrigation, N-application rate, soil water content and soil temperature, Soil Biology Biochemistry 28 (2), 231-237.

Rochette P., Angers D.A., Chantigny, M.H., Bertrand N. and Coté D., 2004. Carbon dioxide and nitrous oxide emissions following fall and spring applications of pig slurry to an agricultural soil, Soil Society of America 68, 1410Nitrogen Workshop 2012 Optimising the spring N fertilisation rate to winter oilseed rape Engström, L.

Precision Agriculture and Pedometrics, Department of Soil and Environment, Swedish University of Agricultural Sciences, PO Box 234, SE-532 23 Skara, Sweden

1. Background & Objectives Field experiments in Sweden show that with higher nitrogen (N) fertilisation rates at sowing of winter oilseed rape (Brassica napus L.) the spring N rate can be reduced without any yield loss.

This suggests a negative relationship between N uptake in late autumn and the spring optimum N rate, which German field experiments have confirmed (Henke et al., 2009). Optimising the spring N-rate to winter oilseed rape will reduce the costs and also the risk for N leaching in the following crop, often winter wheat (Engström et al., 2011). In this ongoing study we investigate the influence of four different factors on economic optimum N rate in spring: N uptake in autumn, N uptake in spring, plant available soil N from spring to after flowering and yield level. The aim is to improve current N fertilisation recommendations to winter oilseed rape, which are mainly based on yield level at present.

2. Materials & Methods Six field experiments, at six sites with contrasting cropping and N-input history (slurry or turkey manure application), were performed during 2010/2011 and another six are being performed during 2011/2012 in the south of Sweden. Six treatment plots (3 m x 15 m each) with increasing spring N rates (0-220 kg N ha-1) were fully randomized, with four replicates (in total 24 plots) and placed in the farmers fields of winter oilseed rape. The mineral N fertiliser (50 % of each ammonium and nitrate) was applied at the beginning of growth in March-April. Yield was determined by combineharvesting a 20-25 m2 area of each plot. Plant N uptake was determined in late autumn, early spring and just after flowering (in unfertilised plots) by analyzing crop samples cut in 1 m2 of each plot.

Plant available soil N from early spring to after flowering (June) was calculated by subtracting N uptake in early spring from N uptake after flowering. Economical optimum N fertilisation was determined as the N rate at the highest net income, assuming a seed price of 3.3 Swedish kronor kgN cost of 9 Swedish kronor kg-1 and cost for transport and drying 0.2 Swedish kronor kg-1. Single and multiple regressions were conducted to ascertain how the four factors could explain the variation of the optimum N rate. In this paper data from the first six field experiments are presented.

3. Results & Discussion N uptake at all six sites varied between 5 and 104 kg N ha-1 in late autumn, and between 3 and 77 kg N ha-1 in spring. Plant available soil N from spring to after flowering was 20-40 kg N ha-1 with cereal and grass leys as preceding crops, and 60-80 kg N ha-1 with peas and at sites with manure applied before sowing. Yields ranged from 980 to 4200 in unfertilised plots and from 3140 to 4700 at optimum N rate. The yield response to N fertilisation in spring was the highest at sites with low yields in unfertilised plots and the lowest at sites with high yields (Figure 1). Yield level in unfertilised plots correlated negatively (significantly, p0.05) to optimum N rate in spring (R=0.93) probably reflecting soil N availability at the site. There was a significant negative correlation between optimum N rate in spring and N uptake in late autumn (R=0.74) and also with yield at optimum (R=0.74). The correlation was not significant between optimum N rate in spring and N uptake in spring or plant available soil N from spring to after flowering. According to the multiple regression analysis, optimum N rate in spring was best explained by N uptake in late autumn and

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Figure 1. Yield response (9% water content) to spring N fertilisation and optimum N rate (by arrows) in six field experiments (Gärsnäs 1-2, Övraby 1-2, Long and Skara) with different preceding crops (grass ley, barley, peas, set aside land) and manure application (slurry and turkey manure) before sowing of winter oilseed rape (n= 4).

4. Conclusion Highest net income was achieved with winter oilseed rape after peas or when fertilised with farm yard manure before sowing. At these sites yields were the highest and optimum N rate the lowest.

The results suggest that N uptake in autumn or spring and plant available soil N from spring to flowering could be used to estimate optimum N rate in spring.

References Engström, L, Stenberg, M., Aronsson, H. and Lindén, B. 2011. Reducing nitrate leaching after winter oilseed rape and peas in mild and cold winters. Agronomy for Sustainable Development 31, 337-347.

Henke, J., Sieling, K., Sauermann, W. and Kage, H. 2009. Analysing soil and canopy factors affecting optimum nitrogen fertilization rates of oilseed rape (Brassica napus). Journal of Agricultural Science 147, 1-8.

Nitrogen Workshop 2012

Physicochemical changes and nitrogen losses during composting of Acacia longifolia and Acacia melanoxylon Brito, L.M., Mourão, I.

Mountain Research Center (CIMO), Instituto Politécnico de Viana do Castelo, Escola Superior Agrária, Refóios, 4990Ponte de Lima, Portugal.

1. Background & Objectives Acacias are invasive Fabaceae species and a serious threat to local biodiversity and natural habitats.

Taking into account their high availability and low cost, a valorisation approach for acacia shrubs may be composting to produce horticultural organic amendments and substrate components.

Acacias have large recalcitrant lignin, polyphenol and cellulose contents (Baggie et al., 2004) that do not contribute to raise composting temperatures. However, they are also rich in N whereas other conditions, including particle size, pile dimension and turning frequency (Brito et al., 2008) affect heat loss and pile temperature. The objectives of this work were to investigate the physicochemical characteristics and to model the breakdown of OM and N losses during composting of ground and screened acacia shrubs with different pile turning frequency, and to find out if composting acacia may reach high enough temperatures for compost sanitation and weed seed destruction.

2. Materials & Methods Acacia longifolia and Acacia melanoxylon shrubs (particles 40 mm) collected in Portugal (at 40º25' N 8º44' W) were composted in big piles (100 m3) with higher (A) and lower (B) turning frequency. Temperatures were monitored automatically with thermistors positioned at 0.5, 1.5 and

2.5 m high and recorded by a data logger. Physicochemical characteristics were periodically determined by European standard procedures. OM and N losses were calculated from the initial and final ash and N contents according to the formulas of Paredes et al. (2000). Mineralization of OM during composting, determined by the OM lost, was described by the following two component

kinetic model (adapted from the N mineralization model of Molina et al. (1980)):

OM m  OM 1 (1  e  k1t )  OM 2 (1  e  k 2t ) [1] Were OM1 and OM2 are pools of mineralisable OM (OMm), k1 and k2 the respective rates of mineralization (day-1), and t the time (days). Data referring to OM losses during composting was fitted to the kinetic equation by the non-linear least-square curve-fitting technique (Marquardt– Levenberg algorithm). The same procedure followed for OM was carried out to describe N losses.

3. Results & Discussion Time-temperature conditions in acacia piles exceeded the more stringent criteria for complete pathogen inactivation proposed by Wu and Smith (1999) equivalent to 55ºC for ≥15 days, as temperatures were kept between 65ºC and 75ºC for 6 months, indicating high total amount of biodegradable OM in the composting material. As a consequence of the degradation of organic acids and ammonia production, the pH increased early during the process and thereafter was in the range 7.0-7.6. Organic matter mineralization (640-690 g kg-1 of the initial OM, after 231 days of composting), showed two different phases of OM degradation (Figure 1). The first was indicative of the rapid decomposition of the readily biodegradable substrates and a high rate of microbial activity. The second phase showed a slower rate of OM degradation when only the more resistant compounds remained. The rates of mineralization were increased with increased turning frequency.

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Total N content increased from initial values of 9.5 g kg-1 DM to final values of 11.5−12.3 g kg-1 DM. An increase in total N content during composting has been widely reported (de Bertoldi and Civilini, 2006; Brito et al., 2008), and is due to a lower rate of N loss than OM loss. As expected, NO3--N content in composting piles (data not shown) was negligible because the bacteria responsible for nitrification are strongly inhibited by temperatures greater than 40 °C. This implies that the risk of N leaching was insignificant during this composting period. However, high temperature and high pH conditions during the thermophilic stage probably promoted intense ammonia emission, which would explain high N losses (460 g kg-1 of the initial N) found during acacia composting (Figure 1), mostly at the initial phase of the process when OM degradation and ammonia production was at its most rapid. Differences in N losses between piles were not significant. The C/N ratio declined from 50 at the beginning of composting to final values of 29-32 showing a higher OM mineralization compared to N volatilization (de Bertoldi and Civilini, 2006).

The low electrical conductivity (1.3 dS m-1) together with high OM and N contents in acacia composts suggests that they are suitable as organic soil amendments for agricultural land.

4. Conclusion This work highlights that ground and screened acacia shrubs have sufficient biodegradability and structure to allow effective composting with increased OM losses compared to N losses.

Acknowledgements This work was supported by the QREN/COMPETE/CEI_13584 project, funded by the EU.

References Baggie, I., Rowell, D.L., Robinson, J.S. and Warren, G.P. 2004. Decomposition and phosphorus release from organic residues as affected by residue quality and added inorganic phosphorus. Agroforestry Systems 63, 125-131.

Brito, L.M., Coutinho, J. and Smith, S.R. 2008. Methods to improve the composting process of the solid fraction of dairy cattle slurry. Bioresource Technology 99, 8955-8960.

de Bertoldi, M. and Civilini, M. 2006. High rate composting with innovative process control. Compost Science and Utilization 14, 290-295.

Molina, J.A.E., Clapp, C.E. and Larson, W.E. 1980. Potentially mineralizable nitrogen in soil: The simple exponential model does not apply for the first 12 weeks of incubation. Soil Science Society of America Journal 44, 442-443.

Paredes, C., Roig, A., Bernal, M.P., Sánchez-Monedero, M.A. and Cegarra, J. 2000. Evolution of organic matter and nitrogen during co-composting of olive mill wastewater with solid organic wastes. Biology and Fertility of Soils 20, 222-227.

Wu, N. and Smith, J.E. 1999. Reducing pathogen and vector attraction for biosolids. Biocycle 40(11), 59-61.

Nitrogen Workshop 2012 Polyphenol and cellulose act as a nitrification inhibitor by different mechanisms Sabahi, H., Rezayan, A.H.

Department of Life Science Engineering, Faculty of New Science and Technology, University of Tehran, Iran

1. Background & Objectives Contamination of ground and surface water resources by nitrate (NO3-) is a major environmental concern around the world. Most of the NO3- in ground and surface water are derived from leaching or runoff from agricultural land, especially in winter. One of the measures that has been explored in arable cropping to increase the efficiency of N fertilizers, is to coat the fertilizer with nitrification inhibitors to slow down the conversion of protein (protein of microbial biomass) to NH4+ or NH4+ to NO3-. As part of our research program to develop suitable bio-nitrification inhibitors, here we wish to report new analysis of N mineralization of three N-fast release organic fertilizers.

2. Materials & Methods Coarse and fine meals of three different legume seeds: yellow lupin (Lupinus luteus L.), blue lupin (Lupinus angustifolius L.) and faba bean (Vicia faba L.), were investigated. The fertilizers were mixed with 500g of wet soil (24% w/w) in each jar, in equivalent amounts, corresponding to 200 mg N kg-1 dry soil, (which is equal to about 130 kg N ha-1 incorporated into the uppermost 5 cm).

The experiments were carried out in a randomized block design at 5ºC in incubation chambers containing three layers for the placement of the jars corresponding to three blocks with regular changes in the positions within the blocks. On five occasions (5, 10, 17, 31 and 61 days after the start of the incubation), soil samples (40 g) were taken from each jar to determine mineral N, C and N in microbial biomass and total K2SO4-extractable organic N (TONext ).

3. Results & Discussion To clarify the role of biochemical quality indicators in immobilization of nitrogen, the changes in N turnover during 61 days of incubation were investigated. The results showed that within days 10-17, the sum of increase in NH4+ plus NO3- and TONext was not equal to the decrease in microbial N, which indicated the net immobilization of nitrogen (Table 1). The results were similar for days 31Net immobilization was greater in the fine size fractions than in the coarse size fractions. Fine

size fractions of legume seed meals had lower content of lignin, cellulose, hemicellulose and C:N

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