Agriculture Reference
In-Depth Information
Figure 14.3
Phosphate defi ciency
phosphorous requirement compared with quick-
growing plants that are harvested young.
Deficiency symptoms are related to poor root
development, which leads to reduced growth of stem
and root. There can also be bluish or purplish stem and
leaf colourings with or without speckling associated
this deficiency (Figure 14.3).
Phosphates fertilizers
(containing phosphorus)
commonly used by gardeners and their nutrient
content are given in Table 14.2.
14
Potassium (K)
This is associated with successful flowering and fruiting.
The element is present in relatively large amounts
in plant cells in solution where it acts as an osmotic
regulator - for example, in stomata (see p. 123). It also
has a role in providing hardiness, resistance to chilling
injury, drought and disease in plants.
Mobile
in plant.
Deficiency results in brown, scorched areas on
leaf tips and margins of dicotyledonous plants
(Figure 14.4). Monocotyledons show similar brown
markings at the growing tip of the leaves which
spread down the leaf as the deficiency continues.
Low potassium levels are usually associated with poor
performance of flowers and fruit made worse if large
quantities of nitrogen are added.
Figure 14.2
Nitrogen defi ciency. Note that it is the
lower, older leaves that have been affected before the
younger ones at the top of the plant
of more than it needs can be detrimental as this
interferes with the development of mycorrhiza (see
p. 42). Phosphorus in the plant is constantly being
recycled from the older parts to the new growing
points. This means that older plants have a low
Table 14.2
Nutrient content of
f common fertilizers
N %
P
2
O
5
(P) %
K
2
O (K) %
Mg %
Ca %
S %
Ammonium nitrate
33-35
Ammonium sulphate
20-21
24
Bone meal *
3
20 (9)
Dried blood *
12-14
Hoof and horn*
12-14
Keiserite
16
25
Meat and bone meal*
5-10
18 (8)
Potassium chloride
59 (49)
Potassium sulphate
50 (42)
17
Superphosphate
18-20 (8-9)
20
12-14
Triple superphosphate
47 (20)
14
Urea
46
* an organic fertilizer
