The potential of poo: adding lignite to conserve nitrogen in chicken manure

21 July 2022 by Baobao Pan

Written by Brendon Costello, edited by Ian Lam and Brendon Costello.

Recently, urea – a synthetic nitrogen fertiliser – has seen a sharp increase in price due to issues with global supply. Costing an average of AU$340 per tonne in January 2021, the same amount is now sold or more than AU$1200. In addition to the issue of cost, synthetic nitrogen production also accounts for 2% of global energy use and emissions.

The increase in price of urea is a concerning issue as synthetic nitrogen fertilisers are responsible for feeding around half of the world’s population. Combined with its continuous increase in demand, the time is now to explore innovative and sustainable solutions to decrease our reliance on traditional sources of nitrogen such as urea. To answer this call, a team of researchers at The University of Melbourne have turned to chicken manure, a resource filled with potential for its high abundance of nitrogen.

From ‘waste’ to resource

An unavoidable by-product of intensive poultry production is the large volume of organic ‘waste’ generated. However, terming it ‘waste’ undermines the true potential of chicken manure, considering its nitrogen-rich nature. Instead, we must treat it as a valuable resource given our current reliance on nitrogen fertilisers for global food security.

On the farm level, excess nitrogen from poultry feed is excreted by broilers (meat chickens) in the form of uric acid onto the litter in poultry housing. Uric acid is rapidly broken down by microbes to urea and then to ammonia.

Depending on in-house factors, including litter pH, temperature, and ventilation, ammonia is lost at up to 80% from the litter as a gas. This process causes a substantial loss of nitrogen and contributes to increased soil acidity, eutrophication in waterways (harmful algae blooms) and the further intensification of global warming.

Whilst the concept of using manure as fertiliser is not new, in fact, humanity has been using it for as long as 8000 years; traditional use and handling methods of manure result in significant losses of nitrogen – drastically decreasing its value as a fertiliser. Thus, the time is now to find ways to harness the manure’s full potential and advance nitrogen retention technology to prevent its loss to the environment.

Current advancements in nitrogen retention technology

In a 2021 study, researchers at The University of Melbourne combined lignite with poultry litter in a laboratory experiment. Lignite, a low-grade brown coal abundant in Victoria, is microporous and has rich surface chemistry – characteristics that give it inherent ability to trap ammonia. It was discovered that litter treated with an application rate of 20% lignite reduced ammonia emissions by 42%.

Whilst efficient at retaining nitrogen, there are practical, environmental, and economic limits to how far lignite can be transported and used in commercial broiler housings nationwide. Thus, additional work was performed to dewater lignite (to decrease its weight in water content) and to modify sub-bituminous coal (an alternative to lignite that is more geographically abundant and available), in hopes to combat such issues regarding its limitations in the cost and distance of lignite transport.

The findings were promising and found a 30% and 49% reduction in ammonia emissions for sub-bituminous coal and dewatered lignite, respectively. Whilst shown to be effective at reducing nitrogen loss, applying these materials also decreased soluble organic nitrogen mineralisation and organic carbon decomposition, which have the added benefit of ducing odour and increasing both fertiliser value and available biomass for nutrient cycling in our food systems.

Application and future use

The next step, currently underway, is to test this technology in commercial broiler housing under real-world conditions. This research will not only assess nitrogen loss but also consider odour, animal welfare and production performance. While there is still much work to be completed, the initial results of conserving nitrogen in manure are promising.

This potential to produce an organic fertiliser that can reduce our reliance on synthetic nitrogen inputs, improve the recycling of nutrients, and increase soil carbon, presents us with an opportunity to limit the environmental footprint of our current food production systems.

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