Use of potassium bromide solutions to simulate dairy cow urine flow and retention in pasture soils

Abstract

A series of field experiments determined the amount of dairy cow urine that moved preferentially via a network of soil macropores beyond the 15 cm depth of soil following a urination event onto pasture. Urination events were simulated using potassium bromide solutions and the amount of bromide that was retained within the top 15 cm of the soil profile was measured. The experiments were carried out on seven different soil types, four of which were sampled in two different seasons. Results showed that between 52 and 106% of the applied bromide was retained in the top 15 cm depth of soil, therefore between 0 and 46% of the “urine” was lost beyond this depth as a result of preferential flow. In general, the amount of urine that was lost was more dependent on the physical conditions of the soil surface (e.g., water-repellent or compacted soil surface, irregular surface microtopography, and macropore distribution) than the soil chemical and mineral characteristics or moisture content. These results indicate that preferential flow of urine could result in significant losses of the urine potassium, nitrogen, and sulphur from grazed dairy pastures.

Keywords:

• nutrient cycling
• urine
• preferential flow
• potassium leaching
• nitrogen leaching
• sulphur leaching
• K cycle
• N cycle
• S cycle