Nutrient Management Research Database

Organic fertilisation inevitably leads to heterogeneous distribution of organic matter and nutrients in soil, i.e. due to uneven surface spreading or inhomogeneous incorporation. The resulting localised hotspots of nutrient application will induce various biotic and abiotic nutrient turnover processes and fixation in the residuesphere, giving rise to distinct differences in nutrient availability, soil oxygen content and greenhouse gas (GHG) production. In this study we investigated the spatiotemporal dynamics of the reaction of manure solids and manure solids char with soil, focusing on their phosphorus (P) availability, as current emphasis on improving societal P efficiency through recycling waste or bio-based fertilisers necessitates a sound understanding of their behaviour. Soil layers amended at a constant P application rate with either pig manure solids or char made from pig manure solids were incubated for three weeks between layers of non-amended, P-depleted soil. Spatial and temporal changes in and around the amendment layers were simultaneously investigated in this study using a sandwich sensor consisting of a planar oxygen optode and multi-element diffusive gradients in thin films (DGT) gels, combined with GHG emission measurements. After three weeks of incubation, the soil containing a layer amended with manure solids had a lower overall O₂ content and had emitted significantly more CO₂ than the non-amended control or the char-amended soil. The P availability from manure solids was initially higher than that from the char, but decreased over time, whereas from the char-amended layer P availability increased in the same period. In both treatments, increases in P availability were confined to the amended soil layer and did not greatly affect P availability in the directly adjacent soil layers during the three-week incubation. These results highlight the importance of placing organic P fertilisers close to where the plant roots will grow in order to facilitate optimal fertiliser use efficiency.

• This laboratory study investigated the effects of pig slurry and pig slurry biochar on P availability.
• Soil was alternatively layered with or without the pig slurry amendments.
• Soil oxygen levels and CO2 emissions were monitored over the three week experiment

• While pig slurry initially increased P availability more so than the char, over the course of the experiment, P levels decreased in the pig slurry amended soil.
• On the other hand, pig slurry biochar showed continued increase in P levels through the course of the experiment.
• P levels in non-amended soil layers did not show changes in P availability.
• Pig slurry amended soil showed lower O2 levels and higher CO2 emissions than the biochar amended soil.
• This study shows the importance of applying P close to plant roots to ensure it is plant available.