Quantifying and managing urinary nitrogen

The main source of N pollution in NZ

AgResearch scientists have developed GPS and urine sensors to determine when, where and how much urine is excreted by grazing sheep and cows.

Urine is the major source of N that leaches to ground water and is emitted as nitrous oxide from grazed pastures. Fertiliser N per se accounts for very little of the emitted N, but instead contributes to pollution through increased pasture growth that requires extra livestock to eat it, thereby contributing more urine and increasing N emissions.

Recent research showed that cattle-grazed pastures leached 50% more N than sheep or deer-grazed pastures for every kg o f N consumed. But “does this translate from small flat plots to large hill country paddocks?” and “what paddock features in these environments lead to creation of stock camps which become critical source areas (CSAs) of pollution?”

Remote sensing tools including hyper-spectral imaging are being used to describe within paddock variation in pasture mass and quality which, coupled with GIS layers of topography and urine patterns, are modelled to predict where stock camps will be found. Because 50% of cow urination events were found in just 5-12% of the hill paddock areas, this may allow farmers to cost-effectively target mitigation options to these CSAs to reduce N leaching.

Many N leaching studies using lysimeters apply “average” rates of N to represent sheep or cattle urination events. But limited evidence indicates a very wide range in N load amongst urination events by individual animals even within 24 hours. We are now testing our new urine sensor that quantifies the N load in cow urination event and we are developing a module within APSIM that accommodates spatially variable urinary N loads to more accurately model N transactions in the animal, soil, pasture and atmosphere cycle.

Nutrient transfer models within hill pastures are also being validated using the urine sensors and faecal mapping. These models will be used to update nutrient recommendations within different parts of the landscape and could be used to generate variable rate fertiliser application maps to optimise responses to applied fertiliser while minimising the over-fertilisation that contributes to N and or P pollution.

PhD student Ina Draganova with Dr Ian Yule and Prof Mike Hedley, Massey University, with funding from FertResearch, are using these techniques to describe nutrient transfer around dairy farms. Dr Sharon Aarons, Ellinbank Research Station, DPI, Victoria, Australia is conducting parallel research with dairy cattle. Dr Kensuke Kawamura, Hiroshima University, contributes spatial modelling and hyperspectral imaging expertise to our research programme.

Urine sensor and GPS technologies were developed in conjunction with Datacarter Ltd., Palmerston North, with funding from the FRST Taupo and Nitrogen Programme.