Animal Housing

There are many loss pathways for N after excretion in the animal house, however, the dominant loss is through NH₃ volatilisation. The urea in the excreted urine is rapidly hydrolysed to NH₃ which can be volatilised, especially if it is placed on open surfaces, if pH is alkaline and if temperatures are high (Sommer et al., 2006). Modelling studies indicate that in 2000 almost 30% of the N excreted in animal housing systems in EU-27 was lost during storage; approximately 19% via NH₃ emissions, 7% via nitrification and denitrification (NO, N₂O and N₂) and 4% via N leaching and runoff (Oenema et al., 2007). Another 17% of the N excreted in the housing was lost via NH₃ volatilisation following application. Thus, in total, 48% of the N excreted in animal housing was lost during storage and immediately after application. Because of the significance of this, special attention is paid to this loss route.

During the last decades much research on NH₃ emission reduction has focused on constructional measures for animal houses. The guiding principle is minimising the contact surface and contact time between animal manure and the surrounding air. Examples are decreasing the evaporating area of the manure in the storage pit and frequently removing the manure to an outside storage (Starmans and Van der Hoek, 2007). Measures with respect to animal feeding have effects on excretion and on NH₃ emission. Dutch research on cattle feeding showed a linear relationship between milk urea content and the emissions from housing. An increase in the milk urea concentration from 20 to 40 mg/100 gram milk resulted in increasing emissions from 5 to 9 kg NH₃ per cow in a cubicle cow during the 190-day winter season (Van Duinkerken et al., 2005). The resulting decrease of the NH₄-N content of the manure will, however, reduce volatilisation losses during manure storage and manure application. Dutch research on pig feeding showed reductions in emissions of up to 70% as a combined eff ect of reducing the N content of the feed, additives affecting the pH of the manure and resulting in a change of N in urine into faecal protein (Aarnink and Verstegen, 2007). Emission from solid poultry manure is governed by manure characteristics such as pH, temperature and water content. Microbial breakdown of uric acid and undigested proteins into NH₃ is dependent on moisture content. The positive effect of drying poultry manure on lowering emissions was demonstrated in pilot studies and on practical farms (Groot Koerkamp, 1994; Groot Koerkamp et al., 1998; Starmans and Van der Hoek, 2007).

Many different technologies for reducing housing and storage emissions and improving manure quality have been tested and are increasingly being implemented. These include reducing fouled surface areas in animal houses, covering manure stores, acidification of slurry to reduce pH, slurry separation, biogas digestion, incineration of solid manures, etc. Some of these treatments not only reduce N losses but may have other advantages such as providing energy or increasing the total fertiliser value of the manure. Fewer measures are available for reducing gaseous N losses from solid manures than for slurry, partly because much of the scientific research and technical development has been in areas where slurry is the dominant form and because NH₃ losses from slurry are much greater than from solid manures. Significant losses of NH₃ can occur from stored solid manure, if there is composting or self-heating (Sommer, 2001; Dämmgen and Hutchings, 2008). When implementing measures to reduce N emissions from the manure management system, it is important to take a whole system approach. Reducing NH₃ emissions from animal housing may result in greater emissions from subsequent stages like storage or field application, unless additional measures are taken (Hutchings et al., 1996).