Agriculture Reference
In-Depth Information
Table 5.2.
Quantity of organic compounds and
minerals taken up and captured by hemp at
maturity. (Average of eleven tests: Chambre
d'Agriculture de l'Eure, 1977; FNPC, 1978-1986;
FDGEDA de l'Aube, 1993).
Phosphorus consumption increases slowly
from emergence to the end of flowering.
During this period, it is found mainly in the
leaves. From the end of flowering, the amounts
absorbed are much less important and are des-
tined (>70%) primarily for the seeds.
Organic elements
and minerals
Exports kg/t dry
matter (DM)
Potassium or potash (K
2
O)
Often mistakenly called potash, potassium is
involved in the formation of all plant tissues. It
is found in significant quantities in their ash.
Potassium is critical to the process of pho-
tosynthesis, contributing to the synthesis of
sugars, and it facilitates the migration of prod-
ucts formed in the leaves to the storage organs:
the tubercles, fruit, seeds and roots, etc., thus
improving plant growth and quality.
Nitrogen, potassium and phosphorus
(NPK) are the 'big three' constituents of com-
mercial fertilizers, the 'macronutrients'.
Potassium contributes to resistance to the 'haz-
ards of production' (accidents and disease) and
is indispensable to plant growth, enabling cells
to use more nitrogen and phosphorus and thus
improve crop yields.
Potassium is absorbed rapidly at the start
of the growth cycle, peaking at the start of
flowering. Found predominantly in the leaves,
it is shed with the leaves as senescence sets in.
Its absorption is linked strongly with that of
nitrogen: if nitrogen fertilization is poor, the
plant produces few leaves and therefore uses
little potassium.
N
8.43
P
2
O
5
3.73
K
2
O
17.56
CaO
13.03
MgO
2.13
Na
0.167
Mn
0.515
Cu
0.005
B
0.011
Zn
0.015
and organic compounds synthesized. The
green tissues of the plants are the producers.
Where nitrogen is lacking, leaves become
yellow and plants are stunted; nitrogen is a key
determining factor in plant yields.
Nitrogen is first absorbed very rapidly by
the plant during the early growth phase and
then more slowly until the end of the cycle
(FNPC, 1986, 2000, 2002). Nitrogen levels in
the leaves, fibre and hurds are very high early
in the cycle (6%, 1% and 1%, respectively) and
then decrease progressively with time. At the
end of flowering, consumption increases and
most of the absorbed nitrogen is used to fill the
seeds. At maturity, more than 50% of the
nitrogen is found in the seeds.
Calcium (CaO - calcium oxide)
Phosphorus (P
2
O
5
)
The role played by calcium in soil properties is
well known. It is essential to plant nutrition,
though not to the extant that NPK is.
Like nitrogen, calcium absorption increases
throughout the growth cycle. It is especially rich
in the leaves, fibre and hurds of hemp, but there
is little in the seeds.
Phosphorus is a constituent of all plants. It
plays an important role in the transformation
of chlorophyll, glucose metabolism and the
metabolism of lipids and proteins. It is a growth
factor and is found abundantly in growing tis-
sues. While its effects may be less obvious than
those of nitrogen, it is equally indispensable for
plant development. Its presence allows plants
to absorb and use nitrogen more readily. It has
a positive influence on fertilization, fructifica-
tion and seed formation. It also increases the
rigidity of cereal stems and helps resist any ten-
dency to lodge, as well as improving the lignifi-
cation of the stems.
Copper, zinc, boron (Cu, Zn, B):
the trace elements
Trace elements, as the name implies, are only
found in small concentrations in the soil and,
while essential, are only required in small
amounts by plants. The principal trace elements
