A cost-effective management practice to decrease phosphorus loss from dairy farms

Modeling and Prioritizing Interventions Using Pollution Hotspots for Reducing Nutrients, Atrazine and E. coli Concentrations in a Watershed

Excess nutrients and herbicides remain two major causes of waterbody impairment globally. In an attempt to better understand pollutant sources in the Big Sandy Creek Watershed (BSCW) and the prospects for successful remediation, a program was initiated to assist agricultural producers with the implementation of best management practices (BMPs). The objectives were to (1) simulate BMPs within hotspots to determine reductions in pollutant loads and (2) to determine if water-quality standards are met at the watershed outlet. Regression-based load estimator (LOADEST) was used for determining sediment, nutrient and atrazine loads, while artificial neural networks (ANN) were used for determining E. coli concentrations. With respect to reducing sediment, total nitrogen and total phosphorus loads at hotspots with individual BMPs, implementing grassed waterways resulted in average reductions of 97%, 53% and 65% respectively if implemented all over the hotspots. Although reducing atrazine application rate by 50% in all hotspots was the most effective BMP for reducing atrazine concentrations (21%) at the gauging station 06883940, this reduction was still six times higher than the target concentration. Similarly, with grassed waterways established in all hotspots, the 64% reduction in E. coli concentration was not enough to meet the target at the gauging station. With scaled-down acreage based on the proposed implementation plan, filter strip led to more pollutant reductions at the targeted hotspots. Overall, a combination of filter strip, grassed waterway and atrazine rate reduction will most likely yield measureable improvement both in the hotspots (>20% reduction in sediment, total nitrogen and total phosphorus pollution) and at the gauging station. Despite the model’s uncertainties, the results showed a possibility of using Soil and Water Assessment Tool (SWAT) to assess the effectiveness of various BMPs in agricultural watersheds.

Balancing water-quality threats from nutrients and production in Australian and New Zealand dairy farms under low profit margins

The loss of nitrogen (N) and phosphorus (P) from dairy-farmed land can impair water quality. Efforts to curtail these losses in Australia and New Zealand (Australasia) have involved a mixture of voluntary and regulatory approaches. In the present paper, we summarise the losses of N and P from Australasian dairy farms, examine the policy drivers used for mitigating losses and evaluate the effectiveness of contrasting approaches to implementing mitigations. Median losses for N and P were 27 and 1.6 kg/ha.year respectively, with a wide range of variation (3–153 kg N/ha.year and 0.3–69 kg P/ha.year) caused by a complex array of climate, soil types, flow paths, nutrient surpluses and land management factors. This complexity, coupled with the variable implementation of measures to mitigate losses, means that many voluntary programs to decrease losses have had uncertain or limited success. Although there is little or no formal regulation in Australia, regulation exists in New Zealand that requires regional authorities to implement the best strategy to improve water quality according to regional-specific characteristics. In testing a generalised approach to mitigation (priority given to those that are easy to implement) in four regions in New Zealand, we found that P could be mitigated quite cheaply, but N reductions required more measures, some of which are costly. Conversely, prioritising on the basis of mitigation cost-effectiveness for a specific nutrient will lead to more rapid reductions in losses of the target nutrient, but with fewer co-benefits for the non-target nutrient or other water pollutants, such as faecal microorganisms and sediment. This information will assist farmers in deciding how to meet a catchment target at least cost.