Manipulating Copper Bioavailability and Plant Growth to Mitigate Nitrogen Leaching from Dairy Cattle Urine Patches

This field lysimeter study investigated the effect of late-autumn application of dicyandiamide (DCD), co-poly acrylic-maleic acid (PA-MA), calcium lignosulphonate (LS), a split-application of calcium lignosulphonate (2LS), and a combination of ProGibb SG (GA) and LS (GA + LS) to reduce N leaching losses from Pumice (Manawatu) and Pallic (Canterbury) soils. In a second application, urine only, GA alone and GA + LS treatments were applied mid-winter. Results show that late-autumn application of 2LS and GA + LS treatments significantly (P < 0.05) reduced total N leached by 16% and 34.7%, respectively, from the Pumice soil when compared to urine only. Late-autumn application of DCD, 2LS, and LS + GA to the Pallic soil significantly (P < 0.05) reduced total N leached by 33.6%, 35.1%, and 35.0%, respectively, compared to urine only. Mid-winter application of GA and LS + GA significantly (P < 0.05) reduced total N leached by 23% and 20%, respectively in the Pumice soil relative to urine only treated lysimeters, however, there was no significant effect on total N leached from the Pallic soil. The reduction in leached N due to the 2LS treatment is attributed to a reduction in bioavailable Cu in soil, while that for the GA + LS treatment is attributed to a combination of reduced bioavailable Cu and increased plant growth. Our results demonstrate that treatment of pastoral soil with 2LS and GA + LS can be potential soil amendments to reduce N leaching losses from urine patches