Contaminant leaching through stony soils
Sam Carrick setting up a large scale lysimeter in stony soil (Caroline King).
Farmers usually dispose of dairy shed effluent by irrigating pasture with it so that the soils can re-use the nutrients. However, if irrigation practices are not matched to the soil’s natural capital, excess nutrients leach into ground water.
Over the last decade land use on stony soils has intensified and, while environmental models consistently predict stony soils will be highly susceptible to leaching, relatively little was known in practice about the safe limits for effluent application. We tested this under controlled conditions using stony Canterbury soils.
Results confirmed that, for some land management practices, shallow groundwater under the stonier soils is vulnerable to nitrogen, phosphorous, cadmium and bacterial contamination, which may make it difficult for intensive farming systems to meet regional and national water quality objectives. To reduce leaching losses, particularly in intensively-used irrigated areas, management practices must be closely aligned to the low natural capital and poor environmental performance of stony soils across 1.68 million hectares of eastern New Zealand.