Digging holes for a day’s work

Press, 16 August 1985, Page 18

Digging holes for a day’s work

Digging hundreds of holes to look at soil may not appeal to everyone, but Mrs Jan Heine enjoys her work. She originally trained as a geologist and her interest in the shape of the land and how soils relate to this led naturally to soil survey work.

When she started doing soil surveys for the D.S.I.R.’s Soil Bureau 10 years ago there was only one other woman in this field. However, that did not deter her.

“You do get strong doing this work,” she admitted. “But it does not matter whether you’re a male or a female — you can still dig a hole. Women are doing this work and they are doing it successfully.” A keen tramper and gardener, she does not mind getting her hands dirty. Even when she goes tramping she often takes a cut-down spade with her to do soil observations on the

way, just in case someone might find this information useful.

“I find doing soil surveys really exciting — you can get stories galore about the soil’s history when you do a soil survey. One of the most exciting parts of a soil survey though, for me, is talking to the farmers about their land and relating their management of it to their soils,” Mrs Heine said. To soil scientists like Jan, soil is more than just plain dirt. Soil could be called New Zealand’s most important resource. Farming, and most of the export earnings, are based on the soil. Ne Zealand has hundreds of different kinds of soils, each with its own properties. Soil surveys describe the soils found in a particular area and define their properties and so help ensure the land is used in the most productive way. A soil survey can take three years to complete, with field work taking up around a third of that time. It can be quite tiring, as Jan Heine explains. First she studies aerial photographs of the area where she is going to do a soil survey, looking at features of the landscape which might give clues about the soils underneath. Then she ventures out into the field armed with an auger, a spade and other soil survey paraphernalia.

Mrs Heine uses her scooter to get out to the farms where she does most of her work. In more rugged areas, four-wheel-drive vehicles or helicopters may be used and carrying the equipment, once you get

there can be difficult. Jan Heine has painful memories of thrashing her way through thickets of West coast supplejack while carrying a metre-long auger.

Ideally she has to dig a metre-deep pit for every square centimetre of the final soil map. That can mean 200 to 500 pits and several thousand auger holes. “You get pretty strong digging all these holes. With central North Island volcanic ash soils or loess deposits you can whistle through a metre hole pretty quickly. “But the tough stuff is difficult and you might have to use a crowbar. Wairarapa soils with their clay pans or gravels are among the hardest in dry dry seasons. “Then there’s the Pakihi land on the West coast. You almost need a stick of gelignite to get through the gravels and iron pans.” After digging the pits, Mrs Heine looks at the sequence of soil layers, their colours, textures and structures. She matches the colour of the soil with one of the hundreds of shades in her Munsell soil colour charts. Just the colour of the soil can reveal many things. A dark soil rich in humus is usually good and fertile. But a gray-coloured subsoil shows that it gets waterlogged.

Then came the traditional tests which make soil surveys an art form and could be politely described as a sensory experience.

"I take a lump of soil, wet it up and rub it between my fingers to feel its texture.

You can pick up the different amounts of sand, silt and clay this way. You need lots of spit in this job! "By biting the soil you can also feel the difference. “You muck around with the soil and work it to certain levels of wetness, roll it into a long thread, bend it into a circle to test its plasticity as well as looking at its stickiness.” After doing all her observation, Mrs Heine goes back to her office armed with notebooks and samples to analyse the information. She defines the limits of soil units in the survey area. Laboratory tests on the soil samples range from the nutrient status to what kinds of loads they can carry. All this work results in a soil map. As well as showing where the soils occur, soils are rated on a separate interpretative map according to their limitations for particular uses such as horticulture or irrigation. Other soil properties described may include flood hazard, erodibility, and slope. Soil maps are used by many people. Farmers can use them to estimate potential crop production or stocking capacity, while foresters use them to assess which soils are best for growing trees. Land planners, too, draw up land use schemes with the help of soil maps. This may avoid major mistakes in land use and unnecessary costs. Soils liable to land movement, for example, can be identified during a soil survey and the Soil Bureau can recommend that houses should not be built there.

One of the aims of the Town and Country Planning Act is’ to protect highly productive soils. This is a sensitive area, particularly when there are land use conflicts between market gardening and urban expansion.

Soil maps can also be used to determine which soils are best for reading, buildings, landfills and recreation uses.

Recently Jan Heine became an advisory officer in the Soil Bureau, and now spends much of her time preparing for Town and Country planning hearings, compiling environmental impact reports and the like as well as helping computerise the Soil Bureau’s information on New Zealand soils.

But she still retains her enthusiasm for soil surveys and love of the outdoors and vows that she will still dig the odd hole now and again.