6.1 Maxwell Owusu-Twum – University of Copenhagen

ReUseWaste > Thesis abstracts > 6.1 Maxwell Owusu-Twum

WP 6.1: Field application and gas emissions of slurry treated by additives and mechanical separation, Maxwell Owusu-Twum, UTAD 

The aim of the study was to evaluate the agronomic and environmental consequences of mechanical separation of cattle slurry and slurry additives during anaerobic storage and after field application under a double cropping forage system. The following treatments were studied; cattle whole slurry, liquid fraction, composted solid fraction and the liquid fraction amended with additives (chemical additive, biological additives and a nitrification inhibitor).

During anaerobic storage at 20⁰C, biological additives (EU 200® and Bio-buster®) had no effect on slurry characteristics and gaseous emissions irrespective of the storage duration and slurry composition. However, under slightly acidified conditions a slight increase in ammonium concentration was observed when the EU200® was applied.

Slurry acidification (pH 6) during storage increased sulphur, electrical conductivity, organic matter and dry matter contents. Acidification inhibited the breakdown of cellulose and hemicellulose but had no impacts on the lignin contents. Acidification reduced NH3 emissions significantly but had no effect on emissions of CH4, CO2 and N2O.

The separated slurry fractions (liquid fraction and composted solid fraction) resulted in lower ammonia volatilisation compared to the whole slurry within the first few hours of application. Addition of biological additives (Biobuster® and JASS®) to the liquid fraction did not lead to a reduction in ammonia volatilisation after soil application. The highest cumulative emissions occurred when the whole slurry was applied whiles the lowest cumulative emissions occurred when the acidified liquid fraction was applied.

The whole slurry and the separated fractions led to similar maize forage yield and quality as the mineral fertiliser. The whole slurry and the liquid fractions were comparable to the mineral fertiliser relative to the oat forage yield. Although the mineral fertiliser led to higher forage quality (N removal) than the liquid fraction, the addition of slurry additives (H2SO4 or both H2SO4 + DMPP) to the liquid fraction increased oat forage quality (N removal) to values similar to the mineral fertiliser.

There were no measurable effect of slurry treatments on greenhouse gas emissions during maize forage production. Under laboratory conditions, both DMPP and sulphuric acid-treated slurry reduced NO and N2O emissions relative to the untreated slurry (liquid fraction). However, the DMPP treated slurry had a stronger effect in reduction total nitrogen emissions (NO+N2O) relative to the acidified slurry. Carbon dioxide emissions were reduced in the acid-treated slurry whereas the DMPP treatment had no impact on CO2 emissions relative to untreated slurry.

The findings from this study show that treatment of slurry by mechanical separation and additives can be utilised as a strategy to enhance recycling of slurry nutrients (mainly N) after field application especially under a double crop foraging system.

  • Gaseous emissions and modification of organic fractions in cattle slurry during anaerobic storage: effect of acidification and biological additives. Paper submitted. 

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