Submitted to: World Congress of Soil Science
Publication Type: Abstract Only
Publication Acceptance Date: 3/30/2018
Publication Date: N/A
Technical Abstract: Large volumes of manure generated by intensive dairy production and their final land disposal is a significant environmental problem. Due to the imbalance of nitrogen (N) and phosphorus (P) (4:1), emendation of soils with dairy manure entails a raise in available soil P levels beyond the crops' capacity to absorb P. When emendations are applied to the soil at an agronomic N dose, there is an unnecessary P accumulation in the soils. In order to improve the N and P balance in animal waste prior to soil application, USDA-ARS, Florence, SC researchers developed a process for extracting P from manure solids using mineral or organic acid solutions, and recovery of P from the extract by adding lime and an organic polymer forming a calcium-containing P precipitate. The quick wash process has two products: 1) a washed manure solid with a N:P ratio optimal for use in crop production; and 2) a concentrated solid P material that can be used as an effective P fertilizer. This method can recover P in concentrated solid Ca phosphate. An experiment was made in order to evaluate P removal from dairy manure using the Quick Wash process. The experiment had two treatments (T1 and T2) and a control, with two replicates. In T1, the manure was acidified prior to being passed through a coarse sieve (12-mm). In T2, the manure was first passed through the 12-mm sieve before acid addition. The acid dose used in both treatments was 25 mmol/L of sufuric acid. Thereafter, solids and liquid in the control, T1 and T2 were separated, and the acid extract was used to recover P by precipitation with lime at 2.2 g/L of 10 % lime. Results for the control, T1 and T2 showed recoveries of 35, 44 and 58 % of P in the precipitate with respect to the initial P manure content. XRD analysis revealed that precipitated P was amorphous calcium phosphate with contents of 4, 7 and 8 % P2O5 for control, T1 and T2. We concluded that these precipitates can be used in a comparable way as fertilizer. Thereafter, the N:P ratios of the washed solids in control, T1 and T2 were 6.5, 8.8 and 11.3. Since the majority of C and N remained in washed solids, soil emendations with wash solids were further evaluated with respect to raw dairy manure application for their rate of C and N mineralization in a 70-day soil incubation. Further detailed discussion of the potential use of low-P manure emendations for soil C and N recycling will be included in our presentation.