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Analytical data produced by different soil and plant laboratories appear to show an often distressingly large variability. Soil parameters are, amongst others, used for soil classification and correlation, land evaluation, soil quality, fertility, and pollution assessment. Erroneous data may lead to very costly mistakes by administrators and other authorities and also hamper technology transfer. In an attempt to reduce the observed variability, laboratory cross-checking programmes conducted in the recent past, notably ISRIC's Laboratory Methods and Data Exchange Programme (LABEX), have indicated that this phenomenon can, amongst others, to a large extent be attributed to essentially two causes:

1. High inaccuracy (bias) through lack of standardization of analytical procedures.
2. High imprecision (scattering) caused by lack of within-laboratory consistency.

Efforts to standardize soil analytical procedures on an international level are at present being undertaken by working groups of ISO (International Standardization Organization, Technical Committee 190). The solution of within-laboratory problems has been left to the initiatives of individual institutes. Therefore, particularly commercial laboratories whose success is directly related to the quality of their product, often have a lead here.

It is generally accepted that the quality of the output of laboratories strongly depends on the quality of the organization of the work, not only at the level of execution of the analysis but also at management level ('good tree, good fruits'). To achieve optimal performance, the concept of "Good Laboratory Practice" (GLP) was developed and has been practised now for quite some time by a number of categories of laboratories where the quality of the work is of vital importance, e.g. in the fields of food, medicine, toxicology, pollution, etc.

Implementation of GLP in soil and plant analytical laboratories in a consequent manner has not been done on a large scale yet, particularly not in developing countries, but it seems to be the only way to significantly and structurally improve the laboratory performance.

It is somewhat unfortunate and confusing that GLP as a descriptive general term is in fact, by origin, a rather strict set of regulations for test laboratories. In the context of the present Guidelines the term "Proper Laboratory Practice" would perhaps be more appropriate. Of late, the term "Quality Management" has come into fashion and it is felt that this term fairly well covers the intention of the present book.

In many countries governments are introducing the rule that orders for environmental and ecological analyses should only be given to laboratories that are accredited for this type of work. For accreditation, consequent Quality Management is an essential aspect. It is, however, not the purpose of this paper to guide laboratories to accreditation (at best it could be a start). Accreditation is a ponderous and expensive major undertaking often involving the hiring of specialist consultants and the employment of (extra) personnel trained in laboratory organization and quality assurance. The present objective is rather to introduce a number of basic measures in the laboratory which do not necessarily require a substantial input of capital but may involve a change in attitude and practice of all laboratory personnel. On the other hand, where costs are involved the justification can perhaps be found in an analogy with advertising: 'advertising is expensive, not advertising is more expensive'.

When reading the protocols, operating procedures and other instructions for Good laboratory Practice as part of Quality Management, one may feel that a good many of them are already in practice in one way or the other. Therefore, making an inventory of existing documents should always be a first step. In many cases, however, these concern half-way measures, not properly written up (or filed somewhere and never seen) and the interpretation of which varies from person to person and from time to time. In many cases, notes and calculations are made on odd pieces of paper which happen to lie around. Rejected analytical results or readings are thrown away and malfunctioning apparatus is left to colleagues without notification. Good Laboratory Practice tries to avoid these engrained habits by consequent documentation of all relevant actions ('what isn't written, isn't done'). Cynics sometimes tauntingly refer to GLP as 'Generates Lots of Paper'. Obviously, documentation can be overdone and then it may be counterproductive. In the present manual, too much documentation is consciously avoided. A workable approach is preferred to a fully elaborated procedure involving a drastic change in prevailing practice which may cause evading tactics or an attitude of rejection. Stricter or more comprehensive measures can always be implemented later when the need arises.

A step-by-step approach should in any case be practised with the implementation of all new Quality Management rules and measures. There is a limit to what personnel and a laboratory as a whole can handle, absorb or digest in a limited span of time with a certain budget.

Success depends on the fulfilment of three major preconditions:

1. The directorate of the institute supports (or rather demands) the improvement.
2. The necessary means and time are made available.
3. Participation of all personnel who should be made aware and be involved from the outset.

The first two items are the responsibility of the management of the institute, the third is mainly (but not only) the concern of the laboratory staff. The third condition underscores once again the importance of the cooperation, participation, involvement and contribution of all laboratory staff throughout the implementation of consequent Quality Management.

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