Nutrient Deficiences

Press, Volume CIX, Issue 32274, 17 April 1970, Page 10

Nutrient Deficiences

Some symptoms of nutrient j deficiencies are masked byi the concurrent .occurrence of other deficiencies, or of diseases. Additionally, some symptoms are not easy to distinguish visually from those of certain diseases, or even from insect damage. Very much more often, however, nutrient deficiencies, while sufficiently severe to greatly reduce yields, are not severe enough to produce visible symptoms. For this reason chemical methods are better than visual means to determine the nutrient status of the plant tissue. These tests can be carried out in the field or in the • i laboratory. A field test, or "rapid” test, as it is termed, [ is made on the plant sap to • allow rough estimation of the i presence of a particular element. In the laboratory leaves are the most usually tested, i to obtain an analysis. The latter method could ■ become the major method to •jform a guide to estimation of ! [fertiliser needs for an estabi lished crop. It would be of little use for most short-term I annual crops as they would

I not be in long enough to [derive benefit from subseouent remedial treatment. The maximum potential or real success of this method hinges on standardisation of sampling procedures and analytical methods for each crop. Analysis is related to precise values to standard deficiency levels for particular nutrients in the leaves of a particular plant. This is but a simple explanation of the matter. Leaf analysis differs greatly from soil testing because the latter method requires separate calibration for each new area and has to be related to the nqtrient status of the plant. It could also prove more useful than soil tests for such unstable nutrients as nitrogen. This is because, with such elements, the main problem is how much is present in a soluble form which plant roots can absorb. The amount can vary during the growth of the crop as micro-organisms convert insoluble or unavailable forms, held in soil organic matter, into simpler, soluble compounds containing the nutrient elements.