Diet management to effectively abate N 2 O emissions from surface applied pig slurry

Abstract

Application of manure (uriñe and/or feces) to agricultural soils enhances emissions of gases such as nitrous oxide (N 2 0) and carbón dioxide (C0 2 ). Some minor N compounds such as hippuric acid and benzoic acid present in uriñe can be controlled through diet manipulation to mitígate these emissions. The aim of this study was to evalúate how the inclusión of fibrous by-products in the diet of pigs affects hippuric and benzoic acid concentrations in the excreted urine/slurry, and their possible effect on N 2 0 emissions following application of these manures to soil. Slurries were obtained from growing-finishing pigs fed five contrasting diets: a conventional diet (pig slurry control, PSC); and orange pulp and carob meal at a dietary fiber level of 75 or 150 g kg J (OP-75; OP-150; CM-75; CM-150) and were then applied to mesocosms containing young ryegrass plants. A control treatment without slurry was also included. The N 2 0 and C0 2 emissions were measured using static chambers following slurry application, alongside measurements of soil ammonium (NH 4 + ), nitrate (N0 3 ), and dissolved organic carbón. Soils amended with slurries obtained from fibre by-products, OP and CM, decreased N 2 0 emissions by 65 and 47%, respectively, compared with slurries obtained through a conventional pig diet. Benzoic acid was negatively correlated with N 2 0 emission for slurries from OP diets, which had over double the hippuric acid content, and more than 1.8 times the benzoic acid content than the CM. However, this effect only occurred during the first week due to rapid degradation of this compound within soil. The possible toxic effect of benzoic acid did not appear to affect soil respiration, since a positive correlation was found. Results of a benzoic acid balance (considering both intake through feed and reléase through uriñe) indicated that the source of both acids were phenolic compounds (polyphenolic or lignin) present in the fibrous fraction. These results show that N 2 0 emissions are more affected than C0 2 by to compounds within urine/faeces that can be manipulated indirectly through the diet.

Nutritional value of crude and partially defatted olive cake in finishing pigs and effects on nitrogen balance and gaseous emissions

“…The current results show that the total excretion of benzoic and hippuric acids increased from 1.05 mg/mL in the control diet to 2.38 mg/mL in the 200 g/kg OC diets, in parallel to increasing levels of intake, absorption and excretion of polyphenols and fibre. These values are within the range of values reported in the literature for growing pigs using fibrous ingredients (Sánchez-Martín et al, 2017), but are lower than in ruminants, where hippuric acid accounts for about 5% of the N excreted (Bristow et al, 1992, Bussink andOenema, 1998). Recent studies have demonstrated that both benzoic and hippuric acids may inhibit nitrification in soils, and therefore reduce nitrous oxide emissions from slurry applied to soil (Kool et al, 2006;Sánchez-Martín et al, 2017), which seems to be related with changes in pH and the corresponding reduction of NH 3 emission.…”

“…Total N was determined by steam distillation (APHA, 2005) using an automatic analyser (2300 Kjeltec, Foss Analytical, Hilleroed, Denmark). Hippuric and benzoic acids were analysed directly in urine samples via high performance liquid chromatography (HPLC) on a Varian Pro Star 310 HPLC system (Varian Inc., Palo Alto, CA, USA) following the procedure described by Sánchez-Martín et al (2017).…”

Effects of Orange Pulp Conservation Methods (Dehydrated or Ensiled Sun-Dried) on the Nutritional Value for Finishing Pigs and Implications on Potential Gaseous Emissions from Slurry

“…Total Kjeldahl N (TKN) was determined using an automatic analyzer (2300 Kjeltec, Foss Analytical, Hilleroed, Denmark) according to [ 28 ]. Hippuric and benzoic acids were analyzed directly in urine via high performance liquid chromatography on a WATERS Alliance system (model 2695) following the procedure described by [ 29 ].…”

Meta‐analysis of global livestock urine‐derived nitrous oxide emissions from agricultural soils

“…Nitrous oxide emission factors (EFs) from urine, defined as the % of N input lost as N 2 O after subtracting background emissions, can be affected by variation in soil conditions driven by differences in climate, soil type, latitude and pasture management (Chadwick et al, ; Dijkstra et al, ). Animal diet can also alter N 2 O emissions factors due to impacts on urine composition (Ciganda et al, ; Sanchez‐Martin et al, ). As a result, EFs have been found to vary both spatially and temporally.…”