Sodium Contents in Dairy Cow Urine and Soil Aggregate Sizes Influence the Amount of Nitrogen Lost from Soil

摘要

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 to the ground water as nitrate (NO_3~-) and to the atmosphere as nitrous oxide (N_2O). 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, and 5-7 mm). Then, cow urine with variable Na~+ concentrations (4.3-6.1 g Na~+ L~(-1)) was added to the soil cores. We treated the cores with simulated heavy rains and measured the amounts of calcium (Ca~(2+)), Na+, potassium (K~+), and inorganic-N leached from the soils. N_2O emission rates were also determined throughout the experimental period. Increasing Na~+ concentration in urine decreased the loss of NO_3~- (-20%), after repeatedly applied simulated rain treatments (30 mm × 3), whereas it increased the loss of ammonium (31%) and K~+ (19%). For the loss of Ca~(2+) and the emissions of N_2O, the effect of the Na~+ concentrations was unclear. Field level studies and studies focusing on the mechanisms behind the changes in nutrient losses are needed.