The Basque Institute of Agricultural Research and Development, NEIKER-Tecnalia, has analysed various ways of spreading slurry on arable land with the aim of determining the most appropriate way of cutting the amount of ammonia released into the atmosphere.

The three methods studied were: the traditional splash plate or fan method, hanging pipes, or injection. Of these, injection was revealed to be the most environmentally friendly in terms of ammonia emissions (NH₃), achieving a 93 percent 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 percent of the NH₃ emissions in Europe are reckoned to come from agriculture and the pollutant is extremely potent. Between 30 percent and 40 percent 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 formed part of a project involving research institutes from across Spain. All the experiments used unworked grain fields with stubble to which pig slurry was added using a range of spreading equipment.

In one trial, 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 similar to the splash plate method. The experts did not report any significant differences between the two treatments as regards the release of ammonia into the air.

In another test, 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 percent 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 percent with respect to the traditional fan or splash plate method.

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