Aid to good gardening Soil testing is not difficult

Press, 6 May 1983, Page 11

Aid to good gardening Soil testing is not difficult

GARDENING

by

M.Lusty

Soil testing is now a recognised practice, not only in glasshouse cropping, but also for field crops. Basically, soil testing can be of two distinct forms:

(1) It can be used to indicate the acidity level of the area;

(2) The nutrient or mineral content can be determined.

Testing is a very worthwhile investment at intervals for anyone who goes in for intensive cropping. For those who want not only to maintain the nutrient availability of their

soil, but also to apply any feeding programme to maximum all-round benefits, it is also helpful. Testing for acidity is quite straightforward. It can be roughly determined by using a home soil testing kit, a number of proprietary sets of which are available on the market.

The process involves the addition of various solutions to the soil and comparing it with a colour chart which matches particular levels of acidity. Alternatively, samples of soil can be sent to a reputable firm which specialises in soil testing. Here it will undergo pH tests in the laboratory. . PH indicates the potential hydrogen rating, and shows a range of values between usually about 4 — very acid, and 8, alkaline. The neutral point is 7, while an optimum suitable for most crops, lies approximately between pH 6.4 and pH 6.7. Soil testing for plant nutrient or mineral content is a more complicated procedure. But it is possible to determine the content and availability of such elements as nitrogen, phosphorous, potassium, magnesium, copper, boron, molybdenum, zinc and sulphur. Soil salinity can also be checked.

From such general tests the rates of application of fertilisers required to establish an adequate basic level of fertility are determined. Once the soil has been brought up to this basic level of fertility it is possible to grow any vegetable on it free of obvious deficiency symptoms. Where specific crops are to be grown their particular requirements are generally known and a feeding schedule can be worked out to meet them.

Imbalances can be expected in certain types of soils.

For instance, sandy soils are usually low in all the elements.

There is often a copper deficiency in peat soils. It is not uncommon to find boron and molybdenum shortages in an acid soil, while alkaline or over-limed soils may

require the addition of iron and/or manganese. For testing purposes a composite sample of about 12 random locations from the area should be collected. These should all be core samples taken from places

where soil characteristics are the same and to a depth of about 15cm. Areas which have been specially treated in any way with fertiliser or lime, or which have had a fire on them, should be dealt with separately. Generally, the best time to do soil tests is in late summer or early autumn. At other times the tests may be accurate, but only for the season concerned. Like samples should be well mixed and about %kg utilised for testing. This should be air dried in a clean place and then put in a bag or container. Soil testing kits are avail-

able for conducting these tests as well as the pH one. However, far more reliable results are obtained if the sample is consigned to a professional service which will provide a written report together with relevant advice on the fertiliser requirements of the area’concerned.

There is yet one other method by which soil fertiliser requirements can be determined. This is done by testing the plants which grow in them in much the same, way as the soil. It is a very much more specialised procedure requiring considerably more experience and skill.