Knowledge of the fate of agricultural phosphorus in the environment is of crucial interest for maintaining water quality and sustaining economic agricultural enterprises on the landscape, in Wisconsin as well as elsewhere. Since the question is most properly the long term effect of a particular phosphorusmanagement practice, the only alternative to pure forecasting or prediction is the challenge of extracting pertinent information from long-term experiments that were established for purposes other than evaluating the fate of phosphorus in the environment.

A set of fertility plots established in 1962 at the UW Agricultural Research Station at Arlington, WI, included addition of dairy manure at a rate of 15 ton/acre/yr for 32 years and addition of phosphorus fertilizer for 20 years. Since the cessation of treatment applications in 1994, the plots-have been only minimally disturbed. In a preliminary study, the plots and treatments were re-marked and a number of soil cores to a depth of 1 m representing treatments of immediate interest. Measures HF-extractable P show clear differences in the 20-cm plow layer between those cores amended with mineral P fertilizers and with P-containing dairy manure, presumably reflecting P loading rates. However, the pattern of P distribution with depth below the plow layer is even more striking, with manured soil behaving like a chromatographic column, with available-P enriched as much as 20-cm below the plow layer, whereas the mineral-P treatment affects a depth of only 5 cm below the plow layer. Further work is underway to revisit these long-term plots in a scientifically rigorous manner and “mine” information about the long-term fate of phosphorus in a Wisconsin soil from this long-term experiment.