Ammonia emissions from land application of dilute slurry.

Background Document arising from discussions at the Expert Panel on Mitigating Agricultural Nitrogen (EPMAN-3, Dublin, 24-25 Sept 2009).

For presentation to TFRN-3.[1]

Draft 1

Background

Ammonia emissions following land application of animal manures, whether as liquid slurries or as solid manure, give rise to a significant proportion of the total ammonia emissions from agricultural sources. In the case of slurry, the volatilization of ammonia following surface application has been shown to be significantly correlated to slurry dry matter (DM) content. Ammonia emissions, both in terms of absolute emissions and emissions as a proportion of the total ammoniacal nitrogen (TAN), have been shown to increase with increasing DM content (Genermont and Cellier, 1997; Misselbrook et al., 2005; Misselbrook et al., 2004; Moal et al., 1995; Smith and Chambers, 1995; Smith et al., 2000; Søgaard et al., 2002; Sommer and Olesen, 1991; Stevens et al., 1992).

Mechanism for emission reduction

Ammonia volatilisation following slurry application, as a percentage of TAN applied in slurry, is reduced for low DMslurries due to the effects of dilution on both the physical and chemical characteristics of the slurry.

Physical effects

Sommer (2003) identified slurry DM content as a factor determining the physical characteristics and behaviour of slurry regarding infiltration into soil. As slurry infiltrates soil, the ammonium in solution in slurry is attracted by adsorption onto soil particles, reducing the potential for volatilization. Slurries with lower DM contents have an increased potential for infiltration as the physical obstruction and sealing of soil pores caused by the solid particles in the slurry is reduced. Additionally, the solid particles in slurry have a high water-retention capacity, which can act to further restrict infiltration of slurries with high DM contents into the soil.

Chemical effects

Huijsmans (2003) summarises that the concentration gradient of ammonia across the slurry to air interface, i.e. between the aqueous ammonia in the slurry and the gaseous ammonia in the air, is a driver of ammonia volatilisation. Slurries with higher TAN contents are normally associated with higher ammonia emissions, asthere is a correlation between the concentrations of ammonia and of TAN in slurry. Since slurries with lower DM contents often contain lower TAN contents, the total ammonia emissions are reduced.

Effect of DM content on emissions

There are many single factor regression models that quantify the additive effect of slurry DM on ammonia emissions following landspreading. A summary of a selection ofthese models is shown in Table 1 and Figure 1.Many of these models indicate a linear effect of slurry DM content on ammonia emission, with ammonia emissions estimated to decrease within a range of 3.9 and 6.17% for every 1% decrease in slurry DM content (Misselbrook et al., 2005; Moal et al., 1995; Smith and Chambers, 1995; Smith et al., 2000). Sommer and Olesen (1991) indicate a linear effect on emissions in the first 6 hours after application, but a quadratic effect on total emissions. Søgaard et al. (2002) (the ALFAM model) found a significant effect of DM content as a multiplicative factor, and indicated a 11% decrease in ammonia emissions for every 1% decrease in slurry DM content.

Table 1. Comparison of simple models estimating theisolatedeffect of slurry DM content on ammonia emissions, following broadcast surface application (splashplate). (See also Figure 1).

Reference / DM effect in simple regression models1 / Slurry DM (%) range / TAN (g/kg) range / Comments
Smith and Chambers, 1995 / E = 4.5 + 5.4 D / Cattle slurry
Søgaard et al., 2002 / E = a * 1.108D / 0.8-11.0 / 0.2 - 4.0 / Cattle and pig. Multiplicative
Misselbrook et al., 2005 / E = 27.8 + 3.9 D / 1.9 - 9.2 / 0.4 - 1.9 / Cattle slurry
Misselbrook et al., 2005 / E = 25.3 + 4.3 D / 1.2 - 12.6 / 2.4 - 5.6 / Pig slurry
Sommer and Olesen, 1991 / E = 8.8 + 8.14 D - 0.203 D2 / 0.9 - 22.0 / 1.6 - 3.0 / Cattle slurry
Smith et al., 2000 / E = 6.7 + 6.17 D / 4.0 - 8.8 / 1.1 - 2.0 / Cattle Slurry
1E = emission (NH3-N as a % of TAN applied)
D = Slurry DM (% w/w)

Figure 1. Comparison of simple models estimating the isolatedeffect of slurry DM content on ammonia emissions, following broadcast surface application (splashplate). (See also Table 1).

Slurry DM can be vary naturally due to animal type or diet, or itcan be altered by either by dilution with water or by mechanical separation. A dilution of 100% with water can reduce emissions of ammonia by approximately 50% (Genermont and Cellier, 1997). A combination of separation and dilution resulted in a reduction in ammonia emissions of up to 75% from of broadcast applied cattle slurry (Stevens et al., 1992). Low DM slurries can also occur as a result of rainwater addition over unroofed slurry stores or animal enclosures. Dirty water generated from washing animal handling facilities or milking parlours can also be classified as low DM slurry.

Effective management of low DM slurries

Where slurry DM is low, the emissions of ammonia, both in absolute emissions and as a % of TAN applied, are also low. Dilution of higher DM material, (either before application through water addition or by separation, or during and after application through timing close to rainfall or irrigation) is seen as an effective option for mitigating emissions from high DM slurry.

The ammonia emission reduction benefits of alternative application technologies for reducing ammonia emissions, such as low emission application technologies (band-spreading or injection), or rapid incorporation into soil, will be reduced when low DM slurries are being applied, as the emissions are already so low.

Sommer and Olesen (1991) suggested that the main effect of slurry DM content on ammonia emissions occurs in the interval between 4% and 12%, indicating that emissions from cattle slurry with a DM content below 4% are approaching a minimum level that is achievable.

In a study using pig slurry, Misselbrook et al. (2004)showed that for very dilute slurries (<2% DM), the total emissions following application with broadcast application using splashplate or irrigation were low (typically amounting to only 10% of TAN), and observed that the reduction in emissions as a result of band-spreading application were also very low (c. 5% of TAN). It was also suggested that band-spreading of low DM slurries has a low emission reduction potential as dilute slurry is more likely to flow and cover a large area comparable with splashplate application rather than remain in discrete bands, thus negating the reduced surface area benefits of band-spreading.

Recommendations

Ammonia emission abatement technologies for land application are less applicable to slurries with a low DM content. This is because the estimated emission reductions are so low using the reference technique (splashplate), that further reductions inferred by abatement technologies (such as application timing management, band-spreading, injection or incorporation into soil) offer little additional benefit.

It is therefore recommended that slurry that contains a DM content of ≤ 2% should be exempt from mandatory measures that reduce ammonia emissions from land application of slurry.

References

Genermont, S., and P. Cellier. 1997. A mechanistic model for estimating ammonia volatilization from slurry applied to bare soil. Agricultural and Forest Meteorology 88:145-167.

Huijsmans, J.F.M. 2003. Manure application and ammonia volatilisation PhD Thesis, Wageningen University, Wageningen.

Misselbrook, T.H., F.A. Nicholson, and B.J. Chambers. 2005. Predicting ammonia losses following the application of livestock manure to land. Bioresource Technology 96:159-168.

Misselbrook, T.H., K.A. Smith, D.R. Jackson, and S.L. Gilhespy. 2004. Ammonia emissions from irrigation of dilute pig slurries. Biosystems Engineering 89:473-484.

Moal, J.F., J. Martinez, F. Guiziou, and C.M. Coste. 1995. AMMONIA VOLATILIZATION FOLLOWING SURFACE-APPLIED PIG AND CATTLE SLURRY IN FRANCE. Journal of Agricultural Science 125:245-252.

Smith, K.A., and B.J. Chambers. 1995. Muck: from waste to resource. Utilisation: the impacts and implications. The Agricultural Engineer 50:33-38.

Smith, K.A., D.R. Jackson, T.H. Misselbrook, B.F. Pain, and R.A. Johnson. 2000. Reduction of ammonia emission by slurry application techniques. Journal of Agricultural Engineering Research 77:277-287.

Søgaard, H.T., S.G. Sommer, N.J. Hutchings, H.J.F. M., D.W. Bussink, and F. Nicholson. 2002. Ammonia volatilization from field-applied animal slurry - the ALFAM model. Atmospheric Environment 36:3309-3319.

Sommer, S.G., and J.E. Olesen. 1991. Effects of dry matter content and temperature on ammonia loss from surface-applied cattle slurry. Journal of Environmental Quality 20:679-683.

Sommer, S.G., S. Genermont, P. Cellier, N.J. Hutchings, J.E. Olesen, and T. Morvan. 2003. Processes controlling ammonia emission from livestock slurry in the field. European Journal of Agronomy 19:465-486.

Stevens, R.J., R.J. Laughlin, and J.P. Frost. 1992. EFFECTS OF SEPARATION, DILUTION, WASHING AND ACIDIFICATION ON AMMONIA VOLATILIZATION FROM SURFACE-APPLIED CATTLE SLURRY. Journal of Agricultural Science 119:383-389.

[1] TFRN note: The views expressed in this document highlight a debate started during EPMAN-3, rather than a consensus position arising from that meeting. The document is provided as a stimulus to further discussion at TFRN-3.