Agriculture Reference
In-Depth Information
Diesel energy content Diesel LHV is around 36 MJ
LHV
·
l
−
1
, according to data on trans-
portation fuels [13]. The factor of conversion into primary energy β
diesel
, which accounts
for the total heat value of diesel and the energy consumed to extract, transport and transform
the crude oil, amounts to 1.2 J
tot
·
J
−
1
or 43 MJ
tot
·
l
−
1
[14] (see also Fig. 7).
LHV
4.4.2.
Synthetic fertilizers
We consider the major ones, N, P and K. Quantities are reported in the conventional units
as used in agronomy:
kg of N, P
2
O
5
and K
2
O, respectively.
They are in forms rapidly
assimilable by plants, such as minerals for N.
Application rates Large progress has been done to reduce inputs owing to a better control
and the import of organic fertilizers. ITB reports average rates of
100
±
30 kg
N
·
(ha
·
y)
−
1
[15, 16],
70
±
30 kg
P
2
O
5
·
(ha
·
y)
−
1
and
145
±
50 kg
K
2
O
·
(ha
·
y)
−
1
[17].
Nutrients are present in leaves at the field and in residues at the factory. Except beet pulp
all these organic matters are restored to soil. Pulp export amounts to
4
.
2 t
DM
·
(ha
·
y)
−
1
(Fig. 3). About 10% of pulp dry matter is made of protein (see link to Téréos data in Sub-
section 4.2.). Considering that 5.7 g of protein contains 1 g of N, at least
75 kg
N
·
(ha
·
y)
−
1
of N must be offset by synthetic N input. Taking into account N losses the amount agrees
with above application rate. We can even consider that the demand increases steadily with
pulp and, subsequently, beet root yields. Hence r
N
= 1
.
3
±
0
.
4 kg
N
·
t
−
1
A
P and K contents in pulp are around 0.1 and 0.8% of DM, respectively. Their export
in the pulp is equivalent to about
10 kg
P
2
O
5
·
(ha
·
y)
−
1
and
40 kg
K
2
O
·
(ha
·
y)
−
1
, respec-
tively. Actually the balances of the elements in the soil are more complex. ITB establishes
P and K need based on soil chemical analyzes.
Energy requirements Nitrogen fertilizers derive from ammonia, of which production is
mainly based on the gas fueled Haber-Bosh process (see [18-21] and Section 1 of Chap. 3
in [9]). The most used fertilizer in France, solid ammoniac-nitrate (33.5% N), requires a
net energy from natural gas of about β
N
= 41
MJ
tot
·
kg
−
N
.
P and K synthetic fertilizers are produced from phosphate rocks and sylvinite, respec-
tively.
Phosphate ore is water insoluble and, consequently, not directly assimilable by plants.
As a result, large part of it is transformed into phosphoric acid through an attack by sulfuric
acid. Sulfuric acid is produced from elemental sulfur S, itself an important by-product of
the oil and gas industry [18, 22, 23]. Because of the successive exothermic reactions of
oxidation, S transformation into sulfuric acid can release large amount of heat. Its use
to produce electricity and process steam offsets energy requirements to extract the ore,
concentrate its phosphate content and achieve other operations (sulfuric acid factory is often
integrated with mine operations). Hence β
P
2
O
5
= 0
J
LH V
·
kg
−
1
P
2
O
5
.
Sylvinite is largely recovered from deep evaporites in earth crust. A fully integrated
mine in Canada, working paleolozic evaporite at depth close to
1 000
m, requires 0.68
MJ
e
·
kg
−
1
of electricity and 1.9 MJ
LH V
·
kg
−
1
of fuel [24].
Including requirements
K
2
O
K
2
O
for electricity production and for transport estimate of β
K
2
O
for potash production is
4.5
±
0.3 MJ
tot
·
kg
−
1
K
2
O
.
