Phosphorus Distribution in Dairy Manures
- Zhongqi He *,
- Timothy S. Griffin and
- C. Wayne Honeycutt
The chemical composition of manure P is a key factor determining its potential bioavailability and susceptibility to runoff. The distribution of P forms in 13 dairy manures was investigated with sequential fractionation coupled with orthophosphate-releasing enzymatic hydrolysis. Among the 13 dairy manures, manure total P varied between 4100 and 18300 mg kg−1 dry matter (DM). Water-extractable P was the largest fraction, with inorganic phosphorus (Pi) accounting for 12 to 44% of manure total P (1400–6800 mg kg−1) and organic phosphorus (Po) for 2 to 23% (130–1660 mg kg−1), respectively. In the NaHCO3 fraction, Pi varied between 740 and 4200 mg P kg−1 DM (4–44% of total manure P), and Po varied between 340 and 1550 mg P kg−1 DM (2–27% of total manure P). In the NaOH fraction, Pi fluctuated around 200 mg P kg−1 DM, and Po ranged from 130 to 630 mg P kg−1 DM. Of the enzymatically hydrolyzable Po in the three fractions, phytate-like P dominated, measuring 26 to 605 mg kg−1 DM, whereas monoester P and DNA-like P were relatively low and less variable. Although concentrations of various P forms varied considerably, significant correlations between manure total P and certain P forms were observed. For example, H2O-extracted Pi was correlated with total manure P (R 2 = 0.62), and so was NaOH-extracted Po (R 2 = 0.81). Data also show that the amount of P released by a single extraction with sodium acetate (100 mM, pH 5.0) was equivalent to the sum of P in all three fractions (H2O-, NaHCO3–, and NaOH-extractable P). Thus, a single extraction by sodium acetate buffer could provide an efficient evaluation of plant-available P in animal manure, while the sequential fractionation approach provides more detailed characterization of manure P.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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