Environmental Impact of Dairy Farming in New Zealand

Dairy farming in New Zealand is the intensive production of milk. Milk must go through a process to meet the specific market requirements before it is eventually sold as a dairy product. For farmers to have an optimum yield of milk produced, they will need to ensure their pasture is fertilized. Cows eat grass which is mainly made up of nitrogen and when a cow eats grass, it eats all the nitrogen. Some of the nitrogen stays in the cow and some comes out as urine and feces (NH4 – ammonia), 20% of nitrogen is absorbed by cow and 80% comes out other end and used as effluent. Effluent is an organic fertilizer that contains a mix of water, urine, feces and excess milk that has been washed out of the milking shed. Effluent plays a major part about how much nitrogen is in the soil.

Excessive use of fertilizers has negative effects on the environment. The two most common fertilizers that effect the environment are nitrates and phosphates. Nitrates are water soluble and dissolve in water. Leaching occurs when the soil is waterlogged and can’t absorb anymore nutrients which causes the nitrates to percolate past the root zone and into the water table. Phosphates don’t dissolve too well and sit on the ground and attaches to soil particles. Phosphates enter the waterway by runoff, rather than leaching as heavy rainfall washes the phosphorus into the rivers and streams. Studies have shown that 30% of the phosphorus consumed by cows in their food eventually leaves the farm and enters our waterways. Fertilizing should not be carried out during spring as the nutrients are robbed from the soil because of the high rainfall which leads to leaching and runoff.

Effluent leaching and runoff affect the quality of the water. Nitrates and phosphates are the only fertilizers that impact the environment negatively. On monitored groundwater sites 59% groundwater has E. coli and 12% of New Zealand rivers have higher concentrations of E. coli than normal. There is a trend pattern in water pollution over the past 20 years. In Canterbury, livestock nitrogen leaching has increased 117% since 1990 from 15,000 tons to 33,000 tons in 2017. The amount of nitrates are increasing because there is more intensive farming.

Fertilizer application has increased 300% over the last 10 years. The nitrogen in fertilizer is very harmful once into the waterways because it causes eutrophication. Eutrophication is a body of water that has become enriched with nutrients which induce excessive growth of toxic algal blooms. Algal blooms decrease the oxygen levels in the water as it requires oxygen to grow and decompose. When algae decompose, the nutrients contained in that organic matter are converted into an inorganic form by microorganisms. This process consumes oxygen, which reduces the concentration of dissolved oxygen for aquatic plants and organisms. Successful algal blooms don’t allow sunlight to enter the water and aquatic plants are unable to photosynthesize or survive because of the lack of oxygen from algae decomposition. Marine life is now unable to survive in waterways and will have to go somewhere else or die off. Dead algae build up like black sludge along the bottom of the body of water and undergoes anaerobic digestion which produces methane and CO2. This reduces the water alkalinity because of the absence of sunlight during the process of anaerobic digestion. Temperature also rises several degrees. All of this leads to a decrease in biodiversity in our waterways.

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This pollution of the water effects the recreational uses of rivers. 60% of New Zealand rivers and lakes are un-swimmable due to the unsafe levels of E. coli and Giardia. This can cause a decrease in tourism as it does not go with our clean green image and therefore effect our local economy. Water will not be drinkable and would make you sick from the bacteria in the water.

However, there are ways to make farming more sustainable and not have a negative effect on our environment. Nutrient management is important in ensuring you do a soil test so you know which nutrients your soil is lacking and know the correct ratio of specific fertilizer to apply. The time of your application is important and can financially save you money. Don’t apply fertilizer in early spring because the rainfall will wash away your fertilizer and if you applied a slow-release fertilizer it would have all washed away and the nutrients wouldn’t have been absorbed into the soil. Mid-late spring would be the best time of year for application.

Other mitigating actions to reduce chances of nitrates and phosphates getting into waterways is fencing off and then riparian planting. Waterways on all farms should now be fenced off so stock can’t get into the waterways. Riparian planting acts as a filtration system. Plants absorb the nutrients from the runoff before it reaches the waterways. It acts as a deterrent from any stock that could pollute its waterways and also prevents erosion as the roots hold the soil together. Planting native trees in your riparian patch can increase the biodiversity for New Zealand native species.

Wetlands are the kidneys of the landscape and are another form of riparian planting. Wetlands can be more beneficial than traditional riparian planting as they can remove up to 75% of nitrate runoff. Wetlands hold surface water and slowly release it over time. This helps control flood damage. Wetlands are one of the most biologically diverse ecosystems and are perfect for increasing the biodiversity lost from eutrophication.

There are simple solutions to keeping our waterways protected from leaching and runoff. Knowing how to manage nutrients will help farmers not apply excessive amounts of fertilizer. All farms should have their waterways fenced off from stock and should be planting up their waterways into wetlands and riparian areas can absorb excess nutrients before they get into our waterways.