Manure data as a prerequisite to its sustainable use

Sari Luostarinen,
Senior Scientist,
Natural Resources Institute Finland (Luke),
Finland

Manure is a natural by-product of animal production. It is meant to be recycled back into the field soil to provide crops with nutrients for higher yields and soil with organic matter for maintaining its good condition.

Manure cannot be spread on fields in any quantities or it may cause adverse environmental effects due to nutrient losses into air and waters. In the Baltic Sea region, eutrophication is one of the main concerns threatening the good status of the sea. Manure is one factor posing a risk to nitrogen and phosphorus leakage from agricultural areas.

In the Baltic Sea region, the amount of manure spread is limited by its nutrient content, the characteristics of the soil and the needs of the crop produced. However, the regulation varies between the countries and may not be sufficient to ensuring sustainable manure use. It may still allow e.g. too high doses of manure phosphorus if only nitrogen is used as the limiting nutrient. The regulation may also allow spreading without subsequent sowing due to too low manure storage capacity required. Also, the segregation of animal and crop production causes regional concentration of manure resulting in surplus manure phosphorus and ineffective use of manure nutrients.

To enable more efficient manure use, one vital factor is information on its quantity and composition. Fertilization planning on farm and regional scale is dependent on knowing the nutrient content of manure. Also, data on manure quantity is important as it determines e.g. the manure storage capacity needed to spread the manure only during the growing season.

The excreta from different animals (cattle, pigs, poultry etc.), age groups (e.g. heifer, calf, bull, cow) and production levels (e.g. milk yield, slaughter weight) varies in quantity and composition due to differences in feeding and animal metabolism. Furthermore, the technology choices in animal houses affect the quantity and composition of resulting manure. Manure types to be produced vary from dilute slurry to deep litter with high dry matter content. To know the quantity and composition of these manures is no easy task and they also need to be known on different levels from individual farms to regional and national level. While a farm needs the data for planning and implementing proper manure management and use, on regional and national levels the data is needed to assist in directing animal production and nutrient recycling into more sustainable solutions.

The alternative methods for generating manure data are either manure sampling and chemical analysis or mass balance calculation of which only the calculation enables estimation of manure quantity. Sampling and analysis may work for farm scale; provided that the sample is representative and the analysis methods are suitable for a heterogeneous matrix such as manure.  To use this method for a national average of different manure types (‘table values’), a large dataset of analyzed manure samples is needed.

Mass balance calculation can be used on farm, regional and national scale, but it requires detailed background data to provide high-quality results. The calculation proceeds in three steps: the excreted feces and urine are calculated as the balance between animal uptake of feed and intake as growth, reproduction and product yield (milk, meat, eggs). The excreta are then calculated further as part of manure management in the animal house depending on the technology used, i.e. additions (water, bedding) and gaseous losses are accounted for to provide manure removed from housing. The third step calculates the changes during manure storage, i.e. additions (rain water) and losses (gaseous) to provide manure to be spread on fields.

At the moment, the Baltic Sea countries use different methods for determining manure data. The data is also updated variably, with some countries updating annually and some operating with old information, not comparable to current animal production. The precision of manure management and use as a fertilizer may thus be unequal starting already from the data on manure quantity and nutrient content.

Recommendations for more harmonized and regularly updated generation of manure data were made during the project Manure Standards (19 partners in all Baltic Sea coastal countries, coordination: Natural Resources Institute Finland, main funding: Interreg Baltic Sea Region Programme). The recommendations include specific tools for generating proper manure data (instructions for taking representative manure samples and using proper analysis methods, mass balance calculation tools for farm and regional level) and a vast amount of information on the importance of updated, precise manure data for effective manure use and reduced emissions to air and waters.

The recommendations have also been implemented by Helsinki Commission (HELCOM) as a policy tool to improve the precision and harmonization of manure data in the Baltic Sea region. The ultimate aim is to improve nutrient recycling and reduce emissions.

The use of manure as a fertilizer is important for recycling nutrients already present in the food system. To enable it with efficiency, many changes are needed. The first one in the chain is proper and updated knowledge on manure quantity and composition as the basis of manure use.

E-mail: sari.luostarinen@luke.fi

Expert article 2902

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