The three methods studied were: the traditional splash plate or fan method, hanging pipes, or injection. The last one turned out to be the most environmentally friendly in terms of ammonia emissions (NH₃), as it achieves a 93% cut in NH₃ emissions over the usual method.

The cut in NH₃ emissions caused by spreading slurries and manures on agricultural land is essential for the environment, since 90% of the NH₃ emissions in Europe are reckoned to come from agriculture. Between 30% and 40% of these emissions take place after slurries and manures have been spread on the land. That is why Neiker-Tecnalia has studied, in collaboration with the Navarrese Institute for Agrifood Technologies and Infrastructure (INTIA), the ammonia emissions produced by different methods of spreading slurry on agricultural land.

The research has been carried out as part of a broader project known as FER-GIR within the framework of the Spain-France-Andorra Operational Programme for Territorial Co-operation 2007-2012 (POCTEFA), funded by the European Regional Development Fund (FEDER) and by the Governments of the Basque Autonomous Community and Navarre. The study was carried out in two trials in the Navarrese towns of Ubago and Olite, and a third one in Legarda (Araba-Alava). All the cases involved unworked grain fields with stubble to which pig slurry was added using a range of spreading equipment.

In the trial on the Ubago field a comparison was made between the hanging pipes method and the usual splash plate or fan method; the splash plate method consists of squirting the slurry, which is stored in a tank, in a stream that splashes against a plate and opens up in the form of a fan, thus covering the whole surface of the soil. The hanging pipes method consists of dividing the flow of slurry coming out of the tank and guiding it until it is deposited on the soil by means of a network of pipes separated by a space of about 30 cm between each one. The pipes leave a trickle or line of slurry on the earth. In this test, slurry in a highly liquid state was used in a relatively high dose so that it was spread uniformly all over the plot of land in a way that is very similar to that of the splash plate method. So the experts did not notice any significant differences between the two treatments as regards the release of ammonia into the air.

In Olite, as in Ubago, the traditional fan or splash plate system was compared with the hanging pipes one, but using a smaller dose of slurry and, therefore, achieving a distribution of the slurry in lines without covering the whole surface. At the end of the test, the specialists were able to confirm that the ammonia emissions in the method using hanging pipes were 26% lower with respect to the traditional splash plate or fan method. So, Neiker-Tecnalia recommends the correct use of the system of pipes in order to prevent the slurry from spreading and covering the whole surface.

The third trial, carried out at Legarda, yielded the best results. The plate method was compared with the injector method. The latter form of application was carried out using a machine that drilled a series of furrows about 15 cm deep and separated from each other by 35 cm. Behind each injector was the corresponding pipe through which the slurry fell. As the furrow dug was deep, its walls tended to collapse and cover the slurry. That way, the ammonia emissions were drastically reduced by 93% with respect to the traditional fan or splash plate method.

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