Nick Round-Turner, Information Officer for Crops for Southland, explained how it is now possible to generate soil maps of individual farms or specified areas of land such as the Waituna Catchment.

The Topoclimate survey is far more detailed than the old 1968 Soil Bureau survey upon which most people still rely and provides sufficient detail for land use decisions at a farm, rather than merely regional, scale. A new soil map of the Waituna Catchment, specially prepared for the field day, identifies 18 different soil types - substantially more than indicated on older soil maps.

"The map by itself is not much use," Mr Round-Turner said, "because it only tells you the names of the soils on your farm."

"The really important part of the Topoclimate database is the wealth of detailed physical and chemical information we now have about each soil," he explained. "This is now available to land users in the form of information sheets - one for each soil type."

Each of the 140 or so information sheets includes a colour photograph of a typical profile of that soil and describes where the soil in question is found and how and from what parent material it was formed. There is a brief description of the physical properties of the soil and its 'natural' fertility status. "This fertility information is only a guide and is not a substitute for soil testing, which a farmer still needs in order to determine the fertiliser requirements of a particular paddock," Mr Round-Turner emphasised.

Possibly the most important and valuable information in the soil sheets, especially for members of the Waituna Landcare Group, is the 'Sustainable Management Indicator'. This rates each soil for its vulnerability to physical processes that can impact on the environment and on the long-term sustainability of land use. The vulnerability factors are: structural degradation by long-term cultivation or compaction by heavy stocking and vehicles, nutrient leaching to groundwater, topsoil erodibility by water, organic matter loss, and waterlogging.

Every soil type is also rated according to its versatility for each of four classes of land use: non-arable horticulture, arable farming, intensive pasture, and forestry. For each land use category the information sheet lists the main limitations that restrict versatility, such as steep slopes or vulnerability to nutrient leaching to groundwater or vulnerability to waterlogging or compaction, and suggests management practices that might improve soil versatility.

Crops for Southland is currently refining a new computer programme which enables them to map land according to vulnerability or versatility factors by selecting all soils that share a specified rating and displaying their spatial distribution on screen. "This is an extremely useful tool that takes much of the drudgery out of identifying environmentally sensitive areas," Mr Round-Turner claimed.

"With a few mouse clicks we can also produce a map that shows where the best combinations of soil and climate are to be found in Southland for growing a particular crop."

Topoclimate maps and soil information sheets are available for inspection or purchase at the Venture Southland office at 143 Spey Street, Invercargill, or by phoning Nick Round-Turner on 03 211 1413.