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Roper, Teryl R. (ed.) / Wisconsin Cranberry School 1998 proceedings

DeMoranville, Carolyn
Mineral nutrition: what are the guiding principles?,   pp. 1-7

Page 1

Carolyn DeMoranville 
Cranberry Experiment Station 
University of Massachusetts 
  As early scientists developed the ability to analyze plants, they found
that most of 
the plant was composed of water and organic compounds, and that in most plants
mineral fraction accounted for less than 10% of the dry mass. At that time,
the presence 
of an element in the plant was accepted as proof that the element was essential
to the 
plant. However, it was found that plants often take up and incorporate any
present in the growing medium, sometimes accumulating an element to toxic
levels. By 
the turn of the century, water and sand cultures were being used to study
the mineral 
needs of plants under controlled conditions. In 1939, Arnon and Stout published
criteria for essentiality of a nutrient element: 
  o  The element must be present in the plant for normal growth and completion
of the 
  life cycle. 
  o  The element is required specifically and cannot be replaced by another
  o  The element must be directly involved in growth or metabolism. 
By the turn of the century the major or macronutrients necessary for plant
growth had 
been identified. In addition to carbon (C), hydrogen (H), and oxygen (O),
nitrogen (N), 
phosphorus (P), potassium (K), sulfur (S), calcium (Ca), magnesium (Mg),
and iron (Fe) 
had been shown to be essential. In the first half of the 1900s the minor
or micronutrients 
manganese (Mn), copper (Cu), zinc (Zn), molybdenum (MO), boron (B), and chlorine
(Cl) were identified. The terms macro- and micronutrients are used to distinguish
elements needed in relatively large amounts from those required in only tiny
amounts. In 
no way do these designations mean that any of these elements is less 'essential'
than any 
  Once it was known that certain mineral elements were needed for plant growth,
plant response to the addition of an element that had been lacking was thought
to follow a 
certain pattern of diminishing returns. As one added the deficient element,
plant response 
would be great and then as the deficiency was overcome, response to additional
would be less and less as the growth rate approached its maximum. However,
what we 
find is that the pattern is more likely to be one with an 'inversion point',
where growth 
increases until the element is present in sufficient amounts but declines
again when 
supply of the element becomes excessive (the toxic range). Put simply, if
some is good, 
more is not necessarily better. 
  We can study the response of cranberry plants to the absence of each mineral
element and what happens as we reintroduce it into the medium. But in a field
we are more interested in finding out what factor(s) is limiting growth and
production. In 
addition to the mineral elements, other factors may be limiting to production
or may 
interact with mineral nutrition. We can think of all the essential mineral
and other factors 
as different length staves in a barrel. The shortest stave will determine
how much the 
barrel can hold. If that stave is lengthened (the element is added), the
barrel will hold 

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