Reducing nutrient and sediment losses in surface runoff by selecting cattle supplement feeding areas based on soil type in New Zealand hill country

Nutrient loss in surface runoff from hill country catchments is typically generated from small areas and over short time periods. This study compared nutrient and sediment losses in surface runoff when cattle were fed winter hay supplement on two hill country sub-catchments (∼0.3 ha) with contrasting soil types (imperfectly-drained and well-drained soils). Runoff samples were collected during seven events (June-August). During this period, two herds of 16 pregnant, mixed aged Angus cows were supplemented with 2 kg DM. cow day⁻¹ of hay in a defined feeding area within each sub-catchment. The imperfectly-drained soil measured 4.8 times the volume of surface runoff compared to the well-drained soil. As a result, the imperfectly-drained soil lost 2.5 times the amount of sediment, 6.3 and 5.1 times the amount of total phosphorus (TP) and dissolved reactive phosphorus respectively and 4.5 times the amount of total nitrogen (TN). Surface runoff losses of nitrate-N from the well-drained soil were undetectable over the study period. Whilst overall nutrient losses were low over the short study period (0.22 kg TP ha⁻¹ and 0.68 kg TN ha⁻¹), the results highlight the potential benefit of strategically placing cattle feed supplements on soils less prone to surface runoff to improve freshwater outcomes.