All living plants and creatures need nutrients to survive and thrive. In this video, we’ve asked Ian Power to describe how two key nutrients – nitrogen and phosphorus – move around the farm environment. Ian is an environmental management specialist at Ballance Agri-Nutrients.
IAN POWER – BALLANCE AGRI-NUTRIENTS
Farmers use nutrients to produce food and keep plants and animals healthy. These nutrients come from a mix of natural cycles, fertiliser and feed.Understanding nutrient flows help farmers improve production, nutrient use efficiency and reduce nutrient losses.This is especially true for nitrogen and phosphorus where N and P losses can drive unwanted algae and weed growth in streams and lakes.
Most of the Earth’s P is contained in rock minerals and moves very slowly as land is eroded and soil is formed and reformed. Some P is dissolved directly from rock into groundwater.
Most New Zealand soils are naturally low in P and farmers boost this with P fertiliser. Imported feed also brings P into the farm system. The main P fertiliser in New Zealand is superphosphate, where the P is soluble and easily taken up by plants.
A lot of fertiliser P ends up being strongly held by soil particles. Weathering and soil microbes mobilise this P, as well as soil organic P, making it available to plants via their roots. In a grazing farm, P returns to the soil via animal dung and decomposing plants.
P is removed from the farm via farm products – animals, milk, wool and crops. P can be lost from the farm when heavy rainfall causes surface runoff which transports P contained in soil particles, animal dung and fertiliser. The amount of runoff P depends on the interaction between P sources and runoff pathways, minus any P capture before runoff reaches the receiving water body.
The nitrogen cycle is quite different from the P cycle because most N is in the Earth’s atmosphere. Plants cannot use this N until it is converted into soluble ammonium or nitrate. This happens via N fixing plants like clover, or via fertiliser N manufacture, such as urea. N also arrives via imported feed and even lightning.
N returns to the soil via animal urine and dung. Soil microbes help break down organic N into soluble forms which plants can use.
leaves a farm in farm produce and via losses to the atmosphere and water. The main N loss pathway to water is leaching where soil nitrate N is flushed below the soil root zone by rainfall and irrigation. This N drains to groundwater which moves slowly towards springs, streams and lakes.
Most N leaching on grazing farms comes from animal urine patches which contain more N than plants can use. This is especially true in late autumn and winter when plant growth slows, soils are much wetter and soil drainage is at its greatest.
To sum up, farmers need to manage N and P inputs to meet production goals, while also recognising when and where the main N and P losses occur. Farmers can then act to minimise these losses to waterways and help protect water quality. Your nutrient advisor can help by preparing a nutrient budget and farm environment plan tailored to your needs.