Why we need to know what and where cows are urinating - a urine sensor to improve nitrogen models

Abstract

Urine of grazing livestock is the greatest contributor to leached nitrogen (N) in our environment. While many N cycling models have used average urine excretions as input data, concentration and volume of individual urination events can vary greatly. Stock camps receive large amounts of urine and pose a high risk of N leaching, especially when animals are set stocked over several days. A new urine sensor is described, along with the variation in urine characteristics of break-grazed cows. N leaching was modelled based on sensor data collection, and paddock-scale estimates were compared to those based on average urine data. There was a 10% difference in estimated N leached by two pumice soils, but both leached 10% less N when varying urine values were used compared to average urine values. The new data showed a frequency distribution pattern of urinary N concentration in urination events that differed to that estimated using earlier data. Thus, frequency distribution patterns have a large effect on modelled N leaching loss and need to be based on extensive data collection to increase the confidence in improving estimates of N leaching. Campsites, which occupy 5-15% of a hill country paddock, account for about half of all excreted urine; their locations can be predicted for the targeting of N-loss mitigation strategies using a simple topographic map of the farm. Keywords: nitrogen leaching, urine volume, environment, urinary nitrogen concentration