12 May 1999 Soil Losses in City Plan Disappoint Scientist – protection measures 'urgent'

The ‘gobbling up’ of large tracts of highly productive agricultural land by residential developments as proposed in Christchurch's City Plan has been attacked by Lincoln University soil scientist Professor Kuan Goh.

He says that given the existence of protected national parks, and protected marine reserves, it could be time to consider extending similar official protection to areas containing high class soils.

Professor Goh believes there is an urgent need for intervention in the land market to ensure that high class soils are protected for food production for future generations.

"The City Plan's proposal to cope with future population growth by opening up for residential development large areas of the city's green belt and farmland, which contain some of the best soils in the Christchurch area, is an example of planning driven by market imperatives rather than the desire to protect highly productive agricultural land," he says.

"The message seems to be that the infilling of land with residential and industrial development on the outer fringes of Christchurch is a more important objective in city planning than the preservation of high class soils.

The City Plan appears to have ignored or taken for granted the special attributes of high class soils and their ability to serve the needs of present and future generations both for food and, very importantly, employment opportunities.

"Tendencies evident in the Plan are antithetical to the requirement of safeguarding the life-supporting capacity of our land resource," he says.

Professor Goh says the conservation of high class soils is important because they are unique and finite. They have the unique ability to support actual and potential production of a wide range of crops on a sustained basis. They require lower inputs per unit of food production compared with non-high class soils. Some of the special attributes of high class soils cannot be replaced by technology without considerable expense of energy and money. And above all, once a high class soil is lost its loss is irreversible and permanent.

High class soil is unique because of its special properties, says Professor Goh. It has high inherent fertility; active biological activity; and excellent intrinsic physical attributes such as good water-holding capacity, good aeration, good drainage, it's friable, has crumb structure, adequate depth and is able to sustain good top and root growth of plants.

"How much of these soils do we have and where are they? Recent estimates are that we have only about 5.2% of Class I and Class II high class soils in New Zealand. Within Canterbury these two classes make up only 7.2% of all the soils in the area and they are dispersed across the whole of the region. Thus small losses become significant," he says.

Professor Goh warns that these soils are currently rapidly disappearing from the Canterbury landscape through the intensive development of lifestyle subdivisions.

"A few years ago advertisements for selling lifestyle blocks in Saturday newspapers occupied no more than two columns, today they occupy at least two pages!"

Professor Kuan Goh, Soil, Plant & Ecological Sciences Division, Lincoln University, Canterbury, New Zealand

Ian Collins, Journalist, Lincoln University, Canterbury, New Zealand