Dairy cow urine sodium content and soil aggregate size influence the amount of nitrogen lost from soil

Toru HAMAMOTO1, Yoshitaka UCHIDA2

1 Graduate School of Agriculture, Hokkaido University, Environmental Biogeochemistry Lab, Kita9 Nishi9 Kitaku Sapporo, Hokkaido, Japan, 0608589, www.uchidalab.com, [email protected]

2 Research Faculty of Agriculture, Hokkaido University, Environmental Biogeochemistry Lab, Kita9 Nishi9 Kitaku Sapporo, Hokkaido, Japan, 0608589

Abstract

Cow urine deposition on pasture soils is a major source of N-related environmental impacts in the dairy farming systems. The urine-N can potentially be lost in reactive forms to the groundwater as nitrate (NO3) and to the atmosphere as nitrous oxide (N2O) and ammonia (NH4+). These N-related environmental impacts are possibly related to the sodium (Na+) concentrations in urine. We sampled a pasture soil and separated it into three aggregate size groups (0–3, 3–5, 5–7 mm). Then, cow urine with variable Na+ concentrations (4.3–6.1 g Na+ /l) was added to the soil cores. We treated the cores with simulated heavy rains and measured the amounts of inorganic-N leached from the soils. Increasing Na+ concentration in urine decreased the loss of NO3 (−20%), after repeatedly applied simulated rain treatments (30 mm × 3) but increased the loss of ammonium (31%). Field level studies and studies focusing on the mechanisms behind the changes in nutrient losses are needed.