NPR - Dairy Green: Alternate Dairy Effluent Application Methods (a MAF Sustainable Farming Fund Project). (p124-128)
A large increase in dairy farms and dairy cow numbers in Southland over the last 25 years has had a significant impact on the local environment. Traditional methods of dealing with dairy shed effluent needed to be updated to prevent pollution of surface and ground water. The use of rotating boom travelling irrigators in the mid 1990s up to present have contributed to environmental damage in the region. Effluent runoff, ponding and contamination of water ways by effluent that entered tile and mole drains has been observed. This occurs mainly because of the application rate and soil conditions at the time of application.
A project funded from MAF’s Sustainable Farming Fund allowed studies to be carried out on dairy effluent irrigation. One key finding was travelling irrigators were often not the correct tool for the job when considering soil conditions, application rate, distribution pattern and nutrient loading. The milking season in Southland runs from August to May. Soil moisture conditions can be at field capacity during August and September and April and May and for periods up to three weeks at any other time. Grazing animals during these periods damages soil structure and as a result reduces effluent infiltration rate. Monitoring of soil infiltration rates showed low values especially in spring, some as low as 0mm after 20 minutes. The rate of application with a travelling irrigator can be very high, up to 40mm depth in 30 minutes which causes ponding, runoff and preferential flow to subsurface drains. Nutrient loading was also a potential issue with nitrogen applications ranging from 24 kg/ha up to 90 kg/ha, assuming 15 mm depth was applied.
The studies highlighted some key points. Effluent needs to be applied at a rate that matches infiltration rate. Application should only be when a suitable soil moisture deficit exists and effluent nutrient analysis is important for nutrient budgets.
K-line was trialled as a low rate application method; 4.0mm nozzles gave the best result. The significance of effluent application via K-line to moist or very dry soils was highlighted. K-line has proven benefits for the farmer and environment with reduced nutrient loss and water contamination, more palatable pasture, electricity savings and ease of use.
Regional councils evaluated and accepted low rate application using K-line. This was important as the councils set the conditions in regards to effluent discharge and storage.
Key Words: Dairy shed effluent, low rate application, travelling irrigator, K-line.
