The Fertiliser Association of New Zealand, as part of promoting best management practices in the agricultural industry, is encouraging farmers and growers to routinely monitor soil cadmium levels across New Zealand agricultural land. The intention is to focus on areas such as Waikato, Taranaki and Bay of Plenty where there is a long history of phosphate application.
The programme is about building awareness and making this aspect of soil monitoring routine, explains Vera Power, Chief Executive of the Fertiliser Association.
"Regional council data consistently shows cadmium levels in surface water, groundwater and sediments are well below accepted guideline values and unlikely to have adverse environmental effects. The New Zealand Total Diet Survey also shows us that cadmium concentrations in food are well below recommended levels. Continued stewardship of our soils is part of making sure that this continues."
Cadmium is a naturally-occurring element present at low concentrations in air, water and soils around the world. It naturally occurs as a trace impurity in phosphate rock, from which phosphate fertilisers are made.
Farmers in targeted areas will be invited to monitor their soils.
"Farms with higher soil cadmium levels are mainly based in Waikato, Taranaki and Bay of Plenty," Vera says. "This can be attributed to their long history of phosphate fertiliser use, which the pasture needs to thrive in this region. Before 1996, the industry predominantly used Nauru rock phosphate for the manufacture of superphosphate, which had much higher cadmium levels than rock phosphate used subsequently. It is believed soil cadmium levels in these regions are largely a legacy of this early period, in combination with these soils generally having a high demand for phosphate fertiliser.
"Today we use products that are much lower in cadmium concentration. Long term our goal is to ensure no accumulation of cadmium in New Zealand soils, but we have still a bit of work to do to get there."
Vera says that cadmium tends to accumulate very slowly in soils where phosphate-based fertiliser is regularly used.
"To further improve our knowledge and to introduce soil management options, the industry supports soil cadmium monitoring as part of the regular soil sampling conducted to determine farmers' fertiliser requirements.
"This will enable farmers to manage nutrients responsibly and retain greater flexibility in land-use options over the long term."