Effect of Dairy Manure Slurry Application on Phosphorus Distribution in a No-till Soil.

Quantifying the dynamics of phosphorus within the soil profile can help in explaining mechanisms by which alternative management practices affect the availability of manure phosphorus to crops and runoff waters. We sought to test a new method for mapping soil phosphate in a no-till corn production system with different methods of manure application. To track changes in phosphate availability and trends in P movement, observations were made 1 week, 3 weeks and 6 months after dairy manure was applied with two low disturbance manure incorporation methods, and conventional broadcasting. Specifically, for each sampling period, bicarbonate-saturated anion exchange resin sheets were installed to a depth of 30 cm of the soil profile and allowed to equilibrate for 48-hrs. Four observations were obtained per treatment for each observation time. Soil phosphate that was extracted from the sheet during the equilibration periods was mapped within a grid of a maximum resolution of 9 cm². Results were inconclusive with regard to the spatial distribution of extractable phosphate, with little evidence of expected spatial signatures between the various methods. However, significant temporal trends were observed, with greatest concentrations in extractable phosphate observed at 6 months. Soil moisture is likely an important factor affecting phosphate recovery with this technique. Preliminary observations suggest that this method may be better suited to mapping nitrate distribution in soils.

Abbreviations: ortho-phosphate/bioavailable phosphorus; (μg P cm⁻² soil)