Leaching Losses of Phosphorus Following Fertilizer Applications As Affected By Tillage Practices and Application Methods.

Preferential flow may enhance leaching losses of phosphorus (P) from agricultural soils. It is expected that tillage can destruct continuous macropores in topsoil and therefore reduces leaching P losses.  This study is currently underway and aims to investigate impacts of P application methods on P losses in leachate from a conventionally tilled soil (CT) and a commonly used "modified" no-till soil (MNT, i.e. small grains and soybeans are planted under no-till while some soil disturbance is done prior to planting of corn) in Ontario. Both CT and MNT fields used for soil sampling in this study are adjacent (44° 22' 44.76" N, -79° 33' 58.32" W) and  have similar soil characteristics (e.g. soil texture, soil test P concentration, and pH) and agricultural management history except the difference in tillage practices.  A total of 12 intact soil columns (20-cm i.d., 30-cm depth) were sampled with 6 from each tillage system. A combination of  P application methods  including surface application (SA), pre-application tillage (PA), and post-application incorporation (IN) were applied in a completely randomized design. After 3 days of P application, the first leaching event was conducted by adding deionised water (equivalent of 40-mm rainfall, medium-high rainfall event in Ontario) to each soil column, and then the leaching events are conducted once every 7 days. The results to date indicate that MNT soils tended to produce greater DRP concentration in leachate than CT soils; however, the differences of DRP concentration between them were not significant until the third leaching event. Leachate DRP concentration was observed to follow the order of SA>IN>PA for each leaching event, but the difference between  them were insignificant except between SA and PA in the third leaching event. Regarding the impact on leachate DRP concentration, no interaction was observed between tillage practices and P application methods.