Abstract
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.
Highlights
The application of organic waste as a fertiliser is one means of improving nutrient recirculation within agricultural systems and can reduce dependence on mineral fertiliser production and imports
The O2 levels in soil amended with manure solids and char decreased over time, but contrary to this study's hypothesis, no localised O2 depletion in the soil layer amended with manure solids or char was observed
Manure solids-C was more degradable than char-C and resulted in increased O2 consumption in the manure solids-amended soil
Summary
The application of organic waste as a fertiliser is one means of improving nutrient recirculation within agricultural systems and can reduce dependence on mineral fertiliser production and imports. Several essential plant nutrients contained in organic soil amendments have to be microbially mineralised before becoming plant available. Various mechanisms occurring simultaneously control organic matter turnover in soil (Lützow et al, 2006). Spatial inaccessibility and organo-mineral interactions govern organic matter stability in soils in the long term (Lützow et al, 2006). In the initial phase after organic matter amendment (weeks to months), the quality of the organic amendment, its spatial distribution in the soil and physicochemical soil properties control the decomposition rate and influence the amount of greenhouse gases released (Zhu et al, 2014). These processes controlling nutrient turnover and availability are expected to be highly variable both spatially and temporally
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