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.

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Phosphorus derived from agricultural systems has been found to cause eutrophication of surface waters. To combat this, the specific location of soil profile P release is necessary for development of effective mitigation strategies. This paper describes a P leaching study of two Swedish arable soils, an organic (Typic Haplosaprist) and a mineral soil (Typic Hapludalf), both with high P content. Undisturbed soil columns isolated 0- to 20-, 20- to 40-, 40- to 60-, and 60- to 80-cm depth intervals. These were placed in a rainfall simulator and subjected to four 50-mm rainfall events to identify the origin of P leachate as a function of soil depth interval and physicochemical properties. Phosphorus losses were greatest from the two uppermost layers of both soils after 200 mm of artificial rainfall was applied at 5 mm h. Total P concentration in leachate from the 0- to 20-cm layer ranged from 2.1 to 8.8 mg L for the mineral and 3.7 to 10.3 mg L from the organic soil, with most (95-100%) in dissolved reactive P form. Degree of P saturation correlated well with total P leaching losses from the organic soil ( = 0.84) but not the mineral soil ( = 0.69), suggesting that the presence of Al and Fe (hydr)oxides has a stronger influence on P leaching in the organic soil. Results indicate that both soils have the potential to contribute concentrations of P above those known to cause eutrophication of surface waters.

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Trials were started in spring, summer and autumn to compare the effect of Agrotain-treated urea and standard urea, at application rates of 25, 50, 75 and 100 kg N/ha, on dairy pasture production on a commercial dairy farm in Canterbury. Keywords: nitrogen, urea, Agrotain, pasture, yield