Dairy farming activities

Dairy farms operate to maximise milk production

Dairy farms operate to maximise milk production.

Milk production

Dairy farms are either seasonal (spring-autumn) or town supply (year round) operations. Expansion of the dairy industry over the last 20-30 years is largely due to the rapid conversion of dry stock and forestry land to dairying as well as the intensification of farming methods that has led to an increase in stocking rates (cows per hectare). 

During the milking season, cows are usually milked twice a day. During milking, animal waste (dairy effluent) that accumulates in the milking shed and yard is washed down with high pressure hoses and collected in oxidation ponds. This effluent may also contain other elements, such as spilled milk, soil, animal feed, detergents, and other chemicals (i.e., residue from animal health products such as drenches and antibiotics). Dairy effluent contains organic and inorganic nutrients (especially nitrogen and phosphorus) and contaminants  (e.g., pathogens and sediment ), which all have the potential to impact on water quality and mahinga kai if not disposed of correctly.

Dairy effluent cannot be discharged to water directly and needs to be disposed of either by:

1. Settling effluent in an oxidation pond, then spreading onto land.

2. Irrigating dairy shed effluent directly onto land.

Soil and pasture management

The greatest on-farm contribution of nutrients and pathogens into waterways comes from animal faecal matter and urine. Animals with open access to waterways or that cross streams are especially likely to increase nutrients and pathogens into a stream. During times of heavy rain, waste can wash into waterways via surface runoff from paddocks or tracks and roads. Waterways become especially prone to increased nutrients from faecal matter and fertilisers when there are no fences or riparian vegetation, which exclude stock from waterways and absorb excess nutrients in the runoff.

Increasing the number of cows per hectare (overstocking) to maximise production may have detrimental effects on soil structure (compaction, pugging, and trampling damage), drainage, and productivity, especially when soils are prone to flooding and erosion around waterways, which increases runoff of sediment and associated nutrients. When applying fertilisers, a nutrient budget may be used to calculate the impact of nutrient use and flows within a farm (as fertiliser, effluent, supplements, or transfer by animals). The type of fertilisers used and the grasses and crops grown will also influence overall productivity and environmental impacts.

The application of herbicides to control weeds (ragwort, thistles, and gorse) is common on all farms (dairy, dry stock, or arable). Excess spray residue accumulates and binds to sediment particles which may end up in waterways via runoff or by directly spraying around waterways. The toxicity of these chemical contaminants depends on the type and quantity that are applied.

Water take (irrigation and abstraction)

Some farms rely on water take or abstraction for irrigation of pasture and crops. Irrigation systems may be permanent or semi-permanent, including pop-up systems, fixed above ground, drip and micro systems, and pivot or laterally moving machines.

Irrigated water should be applied to match the needs of the pasture and crops grown, otherwise any excess will be lost to groundwater. Irrigation may increase the risk of fertiliser runoff or nutrient leaching which can lead to the subsequent contamination of stream water, in particular nitrate leaching. However, the most damaging effect of irrigation can be taking too much water and not leaving enough for mahinga kai habitat. Pesticides and herbicides in waterways are often also associated with cropping or horticultural activity.

Farm management and animal health

Keeping good records enables well-informed decisions to be made during the year. Time of calving, shearing, addressing and preventing animal health issues, proper hygiene around sheds, waste disposal, and disease control all contribute to and reduce environmental risks.

'Hot spots' that are likely to contain concentrations of chemicals and effluent, and therefore require careful consideration/control measures, include:

  • chemical spray storage sheds
  • chemical spray equipment wash down areas
  • bulk fuel storage
  • uncontrolled dumping or land filling of chemical containers or other waste products
  • offal pits for animal carcasses and farm waste
  • silage pits
  • animals crossing streams
  • runoff of faecal matter from tracks and roads into streams
  • dipping and drenching yards.