Nutrients and contaminants overview
Topics
5 min read
Nutrients are a key part of the farm system, supporting the growth of pasture and crops. However, various farm practices can lead to the contamination of waterways with nitrogen, phosphorus, sediment, and bacteria like E. coli. Effective management of these losses from farms is essential for supporting waterway health and farm productivity.
Overview
There are four main nutrients and contaminants that can be lost from a farm system, impacting the environment and productivity:
Nitrogen (N): Chemical element present in all living cells and has a major effect on plant quality and growth potential. However, when N is converted to nitrate (NO3-) in the soil it becomes mobile (active). Nitrates can cause negative impacts on freshwater if not taken up by plants. Nitrogen loss also leads to nitrous oxide emissions, which contribute to climate change. Find out more about reducing N loss.
Phosphorus (P): Another chemical element used in plant and animal growth. It readily attaches to soil and organic particles and therefore, unlike N, only a small amount is leached. Instead, it is primarily lost from farmland when soil bound with P is eroded, caught up in overland flow, and runs off into water bodies. Find out more about reducing phosphorus loss.
E coli: A type of bacteria (Escherichia coli) that comes from animal and human faeces. It is used as an indicator of a larger range of pathogens (disease-causing organisms) in freshwater. The presence of pathogens in water presents a risk of illness for humans, for example during swimming, and for stock that drink the water. Find out more about reducing E. coli loss.
Sediment: When soils erode, sediment is washed into streams and rivers. The primary source of sediment loss on a farm is topsoil. Sediment is transported to waterways, dirtying the water, and accumulating on the streambed. This can impact insects and fish by smothering habitat, reducing feeding efficiency, and clogging gills. Find out more about reducing sediment loss.
Hotspots for losing nutrients and contaminants
Knowing how nutrients and contaminants enter and move through a dairy farm system will help you understand where they can potentially be lost to the environment. Observing and managing these hotspots effectively will help improve waterway health, farm productivity and greenhouse gas emissions. Note that leaching is difficult to see.
Stock - dung and urine
Nutrient/contaminant: N, P, E. coli, sediment
How: Runoff, leaching, direct deposition.
Signs:
- Stock on paddocks during wet periods
- Ponding and overland overflow
- Collections of dung in areas of a paddock prone to overland flow/flooding
- Slips or slumps
- Extensive pugging
Stand-off areas
Nutrient/contaminant: N, P, E. coli
How: Runoff or leaching if effluent is not effectively captured.
Signs:
- Effluent running off of pad.
Crops
Nutrient/contaminant: N, P, E. coli, sediment (depending on if the crop is grazed or harvested)
How: Runoff, leaching and erosion from stock, fertiliser applications, cultivation and grazing/harvesting activities.
Signs:
- Effluent or sediment running off into water during grazing of a crop.
- Heavy rain, washing soils off cultivated areas.
- Build-up of dung in highly stocked areas.
- Stock on paddocks during wet periods causing plugging.
- Ruts from vehicle movements.
Supplement and fertiliser storage
Nutrient/contaminant: N and/or P
How: Runoff or leaching from the stack and/or storage area if exposed to elements.
Signs:
- Visible runoff from storage site/s.
Fertiliser application
Nutrient/contaminant: N and/or P
How: Leaching, runoff.
Signs:
- Applying fertiliser when the soil already has adequate amounts, or is wet, or very dry/cracked.
- Applying fertiliser close to or in waterways.
Bridges and culverts
Nutrient/contaminant: N, P, E. coli, sediment
How: Runoff, direct deposition.
Signs:
- Effluent or water containing effluent, running off in channels that lead to water.
- Effluent accumulating in areas where cows congregate.
Races
Nutrient/contaminant: N, P, E. coli, sediment
How: Runoff, direct deposition.
Signs:
- Races in poor condition with potholes and boggy patches.
- Water channels scoured into the race, particularly on steep slopes.
- Effluent, or water containing effluent, running off to surface water.
- Effluent or material build-up.
- Poor drainage.
Effluent irrigation
Nutrient/contaminant: N, P, E. coli
How: Saturation of soils leading to runoff or leaching e.g. if infrastructure is not well-maintained, if effluent is applied at a rate or depth that is too high.
Signs:
- Burst pipes
- Blocked nozzles
- Pumps failing
- Irrigation over or close to water
- Ponding of effluent in paddock
- Dead worms at surface
- Grass browning after application
Effluent ponds and related infrastructure
Nutrient/contaminant: N, P, E. coli
How: Runoff, or leaching due to poorly maintained infrastructure and/or unsealed storage.
Signs:
- Overflow of sump or ponds.
- Pond level lowering without discharge indicates it may be leaking.
- Vegetation on the surface that may cause blockages and system failures.
- Yards with cracked concrete.
Offal pits
Nutrient/contaminant: N, P, E. coli
How: Runoff if the pit is in a location where water can run in and out, or leaching if the pit is located within the groundwater level, or not adequately compacted.
Signs:
- Water in the bottom of the pit or flowing in and out of it.
Natural features of a farm
As well as being able to identify pollution hotspots, it is useful to understand how the natural features of your farm can contribute to losses.
Surface water: Includes rivers, streams, creeks, above ground drains, ponds, lakes, estuaries and wetlands – also consider temporary waterways as they can channel runoff with nutrients and sediment into main waterways during wet periods. Signs that you have excess nutrients entering your surface water include excessive plant growth in water bodies, rivers and streams changing colour after rain, effluent or sediment entering waterways from bridges or culverts, stream or bank erosion, stock access to waterways and stock grazing near waterways.
Groundwater: Assumes similar channels to surface water and will appear in the overlying surface water catchment. There may be places on your farm where groundwater is close to the surface. Fertiliser or effluent application and urine deposits to these areas, particularly when the soil is wet, can increase the risk of leaching to groundwater.
Sub-surface drains: It is important to know the location of subsurface drains on your farm. Application of N, effluent or urine patches to soil above these drains during wet periods can increase the risk of nutrients leaching into the drains.
Soils: Knowing the kinds of soils you have on your farm, and doing regular soil testing, will help you identify the risk of nutrient and contaminant loss.
Steep areas: More likely to have episodes of runoff to water, slips and slumps. Worsened by grazing stock on steep areas during high-risk times and by inadequate planting for slope stabilisation. The risk is that the soil or runoff lost from these areas has N, P and/or E. coli bound to it/dissolved in it that could then be carried to waterways.
Gullies or other low or wet areas: May be dry for long periods of the year, but during wet periods water can wash over the higher surrounding land into these low areas, bringing dung, urine, fertiliser or effluent that is present. These channels often flow into waterways, creating water quality problems.
Improving nutrient management
There are several tools that can help you understand nutrient use and losses from your farm system, however, the main one is a nutrient budget.
A nutrient budget draws on-farm data (location, climate, soil type and management, fertiliser, stock numbers, feed eaten and excreted, supplementary feed etc) to estimate the nutrient flows in a farming system. It is used to set the farm’s annual fertiliser applications and allows you to identify the blocks or paddocks that are vulnerable to nutrient losses. It is a condition of supply for many dairy companies and can also be a regional council requirement.
Your local fertiliser representative or farm consultant will be able to support you in developing a nutrient budget.
Nutrient budgets form the basis for nutrient management plans, which describe how nutrients will be best managed to minimise environmental risk. Both are helpful inputs to a farm environment plan.