Abstract
The excessive application of dairy manure to soils to supply plant nutrients can result in increased offsite nutrient transport and degraded water quality. However, by concentrating nutrients from dairy-waste onto biochar or as biosolids, a viable alternative fertilizer can be produced that will benefit soil health, promote carbon sequestration, and decrease nutrient leaching into surface waters. In this study, a greenhouse experiment was conducted to assess soil phosphorus (P) speciation and barley plant growth in soils amended with dairy-waste treated biochar and fermented manure. Phosphorus characterization in the post-harvest soils was determined using selective extractions, 31 P-NMR and XANES spectroscopy, and isotopic tracing (P-δ 18 O). Selective extractions and NMR spectroscopy revealed that most of the P in the amended soils occurred as inorganic species (>85%). XANES spectroscopy further showed that the soil P occurred as either calcium-P minerals (54%–87%) or adsorbed P (0%–46%) species. Analysis by P-δ 18 O in water and sodium bicarbonate extractions of the treated soils showed that the water-extracted P pool is cycled much faster than the sodium bicarbonate extracted P. Although less than 10% of the total P in the dairy-derived bioproducts was extracted using water, plant productivity in the soils treated with these amendments was the same as that in soils treated with equivalent amounts of conventional nitrogen and P fertilizer. This suggests that dairy-derived bioproducts are good soil amendments to supply nutrients and limit leaching.