Evaluation of mitigation strategies for nitrate leaching on pasture-based dairy systems

Dairy farms are under pressure to increase productivity while reducing environmental impacts. We used the DairyNZ Whole Farm Model (WFM) and APSIM to evaluate the effect of mitigation strategies within an efficient farm (EF) in the Waikato region, NZ, on these targets. Mitigation strategies compared with the baseline farm (BF) included the use of fewer more efficient cows, low nitrogen (N) feed supplements, loafing pads, less N fertiliser and nitrification inhibitor (DCD). To encompass climate affects three different years with average, high and low annual rainfall were modelled. The WFM predicted number of urinations and urinary N loads deposited during individual grazing events were used as an input for APSIM to simulate N leaching from urine patches, as well as from non-urinated areas. Results were aggregated to obtain total N leached on a paddock and farm scale. For all 3 years, farm averaged N leaching was lower, by 20–55%, in the EF compared with the BF farm. DCD reduced leaching in two of the 3 years by 12% and 15%. N leaching was lowest for N deposited in the wet year and highest for the dry year. Milk production was consistently greater for the EF compared to the BF, with an increase in milksolids (MS)/ha ranging from 8% in the wet, to 17% in the dry year.