Manure History and Long‐Term Tillage Effects on Soil Properties and Phosphorus Losses in Runoff

Manure additions to cropland can reduce total P losses in runoff on well‐drained soils due to increased infiltration and reduced soil erosion. Surface residue management in subsequent years may influence the long‐term risk of P losses as the manure‐supplied organic matter decomposes. The effects of manure history and long‐term (8‐yr) tillage [chisel plow (CP) and no‐till (NT)] on P levels in runoff in continuous corn ( Zea mays L.) were investigated on well‐drained silt loam soils of southern and southwestern Wisconsin. Soil P levels (0–15 cm) increased with the frequency of manure applications and P stratification was greater near the surface (0–5 cm) in NT than CP. In CP, soil test P level was linearly related to dissolved P (24–105 g ha −1 ) and bioavailable P (64–272 g ha −1 ) loads in runoff, but not total P (653–1893 g ha −1 ). In NT, P loads were reduced by an average of 57% for dissolved P, 70% for bioavailable P, and 91% for total P compared with CP. This reduction was due to lower sediment concentrations and/or lower runoff volumes in NT. There was no relationship between soil test P levels and runoff P concentrations or loads in NT. Long‐term manure P applications in excess of P removal by corn in CP systems ultimately increased the potential for greater dissolved and bioavailable P losses in runoff by increasing soil P levels. Maintaining high surface residue cover such as those found in long‐term NT corn production systems can mitigate this risk in addition to reducing sediment and particulate P losses.