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News Article

Can changes in animal diet mitigate greenhouse emissions?


Agroindustrial by-products in pig feed found to reduce nitrous oxide emissions in slurry

Applying manure to agricultural soils enhances the emission of gases such as carbon dioxide (CO2) and nitrous oxide (N2O) into the atmosphere. New research from the Universidad Politécnica de Madrid (UPM) and Universitat Politècnica de València (UPV) has found that including agroindustrial by-products in pig feed can reduce N2O emissions of slurry, which is used as manure, by up to 65%. 

The purpose of the study was to alter the ingredients of the pig diet in order to modify the composition of slurry used for manure, as well as to assess whether there would be any impact on N2O emissions.  According to the result of the study, soils amended with slurries obtained from amended diets (using carob and orange pulp) reduced N2O emissions by 65% and 47%, compared with slurries obtained through a traditional pig diet.

The study highlights the potential of alternative methods of animal feeding as a strategy to reduce the greenhouse gas emissions contribution of agriculture.  N2O has a heating potential 300 times higher than that of CO2 and so it it is important to develop effective mitigation strategies.  It is mainly caused by nitrification and denitrification.  When nitrogen fertilizer is added to the soil, it increases its microbiological activity through activating both of these processes.

Until now, measures to mitigate N2O emissions were focussed on crop management.  However, researchers from UPM and UPV have focussed on the start of the chain, where the animal by-products are produced and then used as fertilizers.

The two by-products typical from the Mediterranean region were selected for the study, including orange pulp and carob. These were added into the diets of pigs as a replacement for cereals, ensuring that the amended diet satisfied the animals nutritional needs. 

The team found that components excreted through faces and urine, such as lignin, phenolic compounds and nitrogenous fractions varied according to the diet.  Slurry was used as fertilizers on agricultural soils cultivated with ryegrass, a forage plant used as food for livestock.  The N2O emissions were then compared with the emissions generated in soils with slurry obtained from pigs fed with their usual diet.

The researchers analysed the slurry, which revealed that the amount of hippuric acid and benzoic acid varied according to the type of diet the pigs were fed.  According to the results, emission levels decreased in soils that had higher amounts of benzoic acid, provided by the slurry.  This is because the acid reduced the denitrifying microbial capacity of soils which is the source of much of the N2O emissions entering the atmosphere.  Taking into account that hippuric acid degrades in the soil to form benzoic acid, slurries that contained a higher quantity of these acids released less N2O emissions compared with the rest of the slurries.

Journal Reference

L. Sanchez-Martín, A. Beccaccia, C. De Blas, A. Sanz-Cobena, P. García-Rebollar, F. Estellés, K.A. Marsden, D.R. Chadwick, A. Vallejo. Diet management to effectively abate N 2 O emissions from surface applied pig slurryAgriculture, Ecosystems & Environment, 2017; 239: 1 DOI: 10.1016/j.agee.2016.12.007

 

Article details

  • Author(s)
  • Stephanie Cole
  • Date
  • 27 June 2017
  • Source
  • Universidad Politécnica de Madrid
  • Subject(s)
  • Climate Change
  • Pollution