Solution and Solid State P-31 NMR Characterization of Phosphorus In Organic and Conventional Dairy Manure.

In the northeastern U.S., organic dairy production has increased rapidly in recent years, as Maine, Vermont, Pennsylvania and New York all rank in the top six U.S. states for the number of cows on organic dairy farms. Organic dairy farms have significant differences from conventional counterparts, including fewer imports of protein and energy feeds, a higher proportion of forage crops in the ration, and increased reliance on non-fertilizer nutrient sources, especially manure and compost.  These differences may significantly impact availability, utilization, and cycling of manure nutrients; however, little information is available to aid organic dairy farmers in making nutrient and manure management decisions. In this study, we comparatively characterized P in organic and conventional dairy manure by solution and solid state P-31 NMR spectroscopic techniques. P in the two types of dairy manure was extracted with water, Na acetate buffer (100 mM, pH 5.0) plus 20 mg Na dithionite/ml, or 0.025 M NaOH with 50 mM EDTA, respectively. Solution P-31 NMR analysis of these extracts revealed that organic dairy manure contained about 10% more inorganic phosphate than conventional dairy manure. Whereas organic dairy manure did contain slightly more phytate P, it contained 30-50% less monoester P than  conventional dairy manure. Solid state P-31 NMR analysis of untreated samples and freeze-dried residues after each extraction indicated the major P compounds were present in soluble mono-metal (Na and K) and less soluble di-metal (Ca and Mg) forms.  These results indicate that P transformation rates and quantities should be expected to differ between organic and conventional dairy manures.