Phosphorus Leaching from Two Soils with Catch Crops Exposed to Freeze-Thaw Cycles

Catch crops have been found to decrease leaching of nitrates into surface water and groundwater, but they also have the potential to increase P loadings to natural waters due to plant destruction during freezing-thawing events. An indoor lysimeter experiment was performed using a clay and a sand soil with four different plant species applied: perennial ryegrass (Lolium perenne L.), honey herb (Phacelia tanacetifolia Benth.), chicory (Cichorium intybus L.), and oilseed radish (Raphanus sativus L.). These plants were exposed to simulated rainfall and freezing events in two separate experiments, one using topsoil columns with plant material added and one with plant material only. The sand and clay soils had significantly different control total-P leaching loads after all freezing events, with a mean of 0.32 kg ha(-1) for the clay and 0.88 kg ha(-1) (P < 0.001) for the sand. The combined (soil including plant material) total-P leaching loads from the clay soil were in the order: chicory (2.6 kg ha(-1)) > ryegrass (2.3 kg ha(-1)) > oilseed radish (2.2 kg ha(-1)) > honey herb (1.3 kg ha(-1)), with considerably smaller loads from the sand. Phosphorus losses were greater from the plant-only experiment, with chicory (51.7 kg ha(-1)) > oilseed radish (43.2 kg ha(-1)) > honey herb (18.4 kg ha(-1)) > ryegrass (10 kg ha(-1)). The results indicate that soil texture and plant choice can have a large impact on P leaching loads entering natural waters in cold regions and that soils act as an efficient filter for P released from catch crop residues.