Effect of macropore flow on the transport of surface-applied cow urine through a soil profile

A field lysimeter experiment was conducted to determine the effect of macro pore flow on the transport of surface-applied cow urine N through soil. The lysimeters (500 mm diameter by 700 mm depth) used for this experiment were collected from Templeton fine sandy loam soil (Udic Ustochrept), which had been under ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) pasture for 9-10 years. The effect of macropore flow on urine-N leachi ng was determined by leaching experiments under 0.5 kPa and 0 kPa water ten sions (suctions) imposed on top of the lysimeter using a disc tension infil trometer. The 0.5 kPa suction prevented soil pores >600 mm diameter from co nducting water and solutes, while the 0 kPa suction allowed conduction unde r 'field saturated' condition. Pores >600 mu-m diameter transmitted about 9 8% of the total nitrogen (N) leached below 700 mm depth. The main form of N transmitted under 0 kPa was ammonium (NH4-N), accounting for 10.5% of the total N applied at 0 kPa suction. This was significantly higher than the am ount of NH4-N leached at 0.5 kPa suction, which accounted for 0.17% of N ap plied. The urea-N in the leachate reached 16 mg/L at 0 kPa suction, and acc ounted for 1.6% of the total N applied. No urea was detected in the leachat e at the 0.5 kPa suction. The concentrations and amounts of nitrate (NO3-N) leached were very low and did not differ between the two suctions. The for ms and amounts of N leached were affected by the interactions of macropore flow and N transformations in the soil, and the environmental conditions du ring the two leaching events. From this work, it is recommended that stock should be removed 1-2 days before irrigation water is applied as this will allow animal urine to diffuse into soil micropores and thus decrease N leac hing by macropore flow.