A research of Universidad Politécnica de Madrid (UPM) and Universitat Politècnica de València (UPV) has shown that the inclusion of agroindustrial by-products in pig feed can reduce the nitrous oxide emissions (N 2 O) of the slurry used as manures up to 65%.

The aim of this study carried out by UPM researchers with the collaboration of Institute for Animal Science and Technology of UPV was to influence the ingredients of pig diet to modify the composition of slurry used as manures and to assess the possible variations on N 2 O emissions.

According to the results, soils amended with slurries obtained from modified diets (with orange pulp and carob) decreased N 2 O emissions by 65 and 47%, respectively, compared with slurries obtained through a conventional pig diet. These results show the potential of alternative strategies of animal feeding to reduce the environmental issues associated with agriculture.

Nitrogen fertilizers, organic or mineral, are responsible for most of the N 2 O emissions from agricultural activity. This gas has a heating potential 300 times higher than CO2, this is the reason why it is essential to develop mitigation strategies. N 2 O emissions are mainly caused by microbiological processes known as nitrification and denitrification. When a nitrogen fertilizer is added to the soil, it increases its microbiological activity by activating both processes that at the same time they depend on factors such as such as climatic, edaphic and field management.

So far the measures to mitigate nitrous oxide emissions (N 2 O) were focused on crop management. However, researchers from Universidad Politécnica de Madrid y Universidad Politécnica de Valencia have focused on the beginning of the chain, where the animal by-products are produced and then are revalued as fertilizers.

Two by-products typical from the Mediterranean region were selected to carry out this study, orange pulp and carob. These by-products were added into commercial diets of pigs in substitution of cereals, being respectful with the balance that these diets require to satisfy the animal needs.

It was proved that, without a doubt, the excreted components through feces and urine (slurry), for example nitrogenous fractions, lignin, phenolic compounds, etc., varied according to diet. Slurries were used as fertilizers on agricultural soils cultivated with ryegrass, a forage plant used as food for livestock. The N 2 O emissions were compared to the emissions generated in soils with slurry obtained from pigs fed with a traditional diet.