Winter and early spring are when nutrients – whether introduced as fertiliser or produced by stock – are most at risk of getting lost from farms.
Topsoil erosion due to heavy rains.
This is due to seasonal and other factors such as high rainfall, reduced pasture growth, a huge amount of urine being produced, soil compaction and pugging.
To help farmers keep on top of the implications, for their property’s profitability and impact on the environment, a farm nutrient budget is a valuable indicator of the status of nutrients in a farm system.
It indicates where fertiliser applications are inadequate and leading to a decline in the soil nutrient status. Conversely, it can indicate excessive inputs, which result in a nutrient surplus and greater potential for losses of contaminants to waterways and groundwater.
So the overall objective of nutrient management is to keep nutrients cycling within the farm system, to make them available for promoting growth, and to reduce the losses to a bare minimum to protect the environment.
Most farmers know some nutrients are more prone to loss than others, depending on the nature of the nutrient, soil type and climatic conditions. Therefore, in making decisions about nutrient management, it’s crucial to take into account the channels where loss occurs and characteristics of the individual nutrients.
Besides produce, the channels where nutrients leave farms include atmospheric loss, run-off and leaching. Depending on the production levels and farm management, these figures can vary greatly between farms. Nutrient budgets will provide this information in detail for individual properties.
Soluble nutrients, such as nitrogen, potassium, calcium, magnesium and sulphur, can particularly be lost by leaching when water washes them through the root zone into deeper layers of the soil and they become inaccessible to plant roots. The leaching risk depends on factors, such as soil type, total rainfall, extreme events and the actual quantity of soluble nutrients in the soil.
Avoid oversupplying soil with these soluble nutrients, especially before and during winter, as there’s a very high risk of these getting washed out through the soil.
Nitrogen leaching to groundwater is one of the main environmental risks from intensive farming.
Generally speaking, there will be an increase in nitrate leaching the more fertiliser is used.
In one study, where 400 kilograms of nitrogen per hectare was used, the nitrate concentration in groundwater increased to an average value of almost twice the commonly-accepted recommended maximum for potable water of 11.3 parts per million.
It also revealed gaseous nitrogen losses to the atmosphere increased by about five times between zero and 400 kg/ha treatments.
Phosphorus loss, on the other hand, mainly occurs from erosion and run-off. Research has revealed phosphorus losses will be high in soils with high Olsen-P levels and also on steep to rolling country.
Good practices, including preparing and implementing nutrient budgets, have clear potential to bring about substantial improvements in the quality of our water resources and profits.
Waikato Regional Council is working with other stakeholders to help farmers adopt these practices and strongly supports the use of voluntary guidelines and codes of practices developed by the farming industry, such as the Code of Practice for Nutrient Management, Fertmark and Spreadmark.
Bala Tikkisetty is a sustainable agriculture co-ordinator at Waikato Regional Council. firstname.lastname@example.org or 0800 800 401.