Improving the Use of Liquid Farm-Based Manures in Arable Farming: Case Studies from Germany

The use of organic fertiliser is an important measure to restore or increase soil humus stocks and to recycle nutrients in agricultural production in a useful way. In several regions in Europe, very large amounts of farm-based manure are produced and applied to agricultural land. As a result, a comparatively low use efficiency of the nutrients contained in these organic fertilisers has often been observed in recent decades, with the resulting environmental impacts on non-agricultural ecosystems

(e.g. nitrate leaching into groundwater, phosphate losses to surface waters, gaseous N emissions into the atmosphere). An additional problem is the highly variable nutrient concentration in these heterogeneous liquid manures (e.g. caused by different animal species, feeding and husbandry systems). Stricter legal requirements have made it necessary to develop optimised methods for the application of farm-based manures.

Reliable information on plant nutrient concentrations is an important prerequisite for the targeted use of such farm-based fertilisers. The concentrations of various nutrients (e.g. ammonium-N) can be accurately estimated using simple on-farm methods. On the other hand, the reliability of near-infrared spectroscopy for the characterisation of liquid farm manures when filling slurry tankers or during field application is still the subject of controversial discussions.

Due to legal regulations, the use of splash plates for the application of liquid farm-based manures is now restricted or even prohibited in some regions of Europe. Farmers have to use a trailing hose system, which significantly decreases gaseous ammonia losses. Further reductions of these NH3 losses are possible by open slot injection or direct incorporation of the slurry into the soil. As an alternative technique to reduce ammonia losses, acidification of liquid farm manure is a possible measure. In addition, deep injection of slurry has been found to reduce nitrate leaching and increase nutrient utilisation efficiency (e.g. phosphorus, manganese and zinc) especially when nitrification inhibitors are added to the slurry.

Conclusions are presented, based on the results of the various studies and field trials carried out in Germany regarding the usefulness of these techniques, which can be transferred to other regions in Europe with comparable production conditions.