Plant sampling: a review

Abstract

The steps involved in collecting and handling samples for plant analysis are described under the following headings: purpose for which the sample is collected; sampling statistics; sampling strategies; choice of tissue; sample handling; special sampling techniques. In any application of plant tissue analysis close attention should be given to the approaches which are used to develop the critical values or ranges that are used. In diagnostic and prognostic use of plant analysis the statistics of the sampling procedure should be well understood, so that a sample which properly represents the crop or planting can be collected. When diagnosis is the primary objective the sampling unit may be as small as a single plant. It is important that contamination of the sample with nutrient sprays or other materials is understood and recorded. Washing may not be possible, particularly when samples are collected by unskilled people at a site distant from the analytical laboratory. Although washing with detergents or weak acids can remove contamination, there will remain some doubt as to the efficiency of the washing procedure. Samples which are to be used for sap tests immediately after collection for nitrate-nitrogen should be handled more carefully than those destined after drying for multi-element analysis at a remote laboratory. Ideally the respiratory loss of dry weight from samples should be minimised when the samples are destined for conventional multi-element analysis. Where certain aspects of sample handling are critical to the success of the test they should be emphasised to potential users. A wide range of plant tissues other than the commonly collected leaves and petioles has been used for assessment of mineral nutrient status, including juice, fruit, and shoot tips. Each of these presents different problems in sample collection handling and storage. Tests based on enzyme activity and other biochemical or physiological indicators probably present the most difficult sample handling problems, but these tests are not widely used. A number of sampling issues which arise from the author's experience with commercial tissue analysis services are raised. These include such matters as the extent of training of the personnel who do the sampling, contamination and transport to the laboratory. Although more attention to these issues is needed in practice, plant tissue analysis continues to be a most valuable tool in the hands of the informed manager.