Phosphorus 31 nuclear magnetic resonance spectroscopy to trace organic dung phosphorus in a temperate grassland soil

Cattle dung contributes to hot-spot inputs of nutrients to grassland systems, but not much is known about its organic P (Po) composition and fate in the grassland soils. We used 31Phosphorus (P)–Nuclear Magnetic–Resonance (NMR) spectroscopy of alkaline soil extracts to examine potentials for tracing of different functional Po forms into a temperate grassland soil amended with dung. The proportion of monoester, DNA-diester, and phospholipid+teichoic acid P were comparable in dung extracts, but the soil was dominated by monoester P. The temporal trends in the DNA-diester P–to–monoester P (DDNAM) and diester P–to–monoester P (DM) ratio of dung, native soil, and soil amended with dung were monitored in the 70 d field experiment. The DDNAM and DM ratio in the dung-amended soil (0–1 and 1–5 cm depth) were always intermediate between the dung and (unamended) control soil. Clearly, extracted soil P was a mixture of incorporated dung-derived P and native soil P. The dung-P contribution in the 0–1 cm samples peaked at 47% of the total extracted P at day 70 and at 15% after 42 d in the 1–5 cm soil depth (based on the DM ratio). The proportions of dung-derived P and C in the soil were positively correlated with: 1) topsoil, using the DDNAM ratio (r2 = 0.975), and 2) top- and subsoil, using the DM ratio (r2 = 0.656). We concluded that our DDNAM and DM-P ratios approach (obtained from solution-31P NMR) did trace successfully the short-term dynamics and fate of dung Po in soil. It indicated that dung-derived Po varied as rapidly in soil as the dung-derived C.