Mineral Balance

To estimate the amount of nutrients needed for fertilization of the soil, an estimate of the nutrient balance is needed. The plant density and the climate are important (IFA 2008). Nutrient stocks have been restricted to the upper 30 cm, as most feeding roots of cacao are concentrated at that depth. Removal of nutrients from cacao ecosystems is caused by yield (beans and husks), immobilization in stem and branches, and leaching of nutrients below the rooting zone (Hartemink 2005). Most nutrients in cacao ecosystems are lost by the harvest of beans and husks. In Table 8.4, an overview is given of the nutrient removal caused by the crop of 1 ha (740 kg dry cacao beans and 1.0 t cacao husks).

For the nutrient demand there are several recommendations for cacao. The recommendations for the nutrient demand for 1 ha of cacao plantation differ hugely, as shown in Table 8.5. We decided to use the statistical approach: all improbable data have been removed.

For the mineral balance it is assumed that the husks are returned to the soil and that all the available nutrients are reused. This assumption is assessed in the sensitivity analysis. In Table 8.6, an overview is given of the mineral balance. The husks are supposed to be returned to the soil, so these nutrients are directly

Table 8.4 Nutrient removal in kilograms caused by the crop of 1 ha of plantation in Cote d’Ivoire (IFA 2008)________________________________________________________________

Beans (+shells)

Husks

Total

N P2O5 K2O

MgO

CaO

N

P2O5

K2O

MgO

CaO

N

P2O5

K2O

MgO

CaO

16.4 5.0 6.7

1.7

0.4

9.8

3.1

38.4

6.9

3.1

26.1

8.1

45.1

8.6

3.6

Table 8.5 Fertility recommendations according to different literature

sources (kg/ha)

References

N

P

K

Elzebroek and Wind (2008)

50-100

25

75

FAO (2009)

0

28

32

CABI (2009)a

200

25

300

Uribe et al. (2001)

100

90

200

IFA (2008)

147

8

106

CPCRI (2009)

110

10

64

Average

126

26

202

aBefore pod production

Table 8.6 Mineral balance for a cacao

plantation in Cote d’Ivoire (kg/ha)

Nutrient

Addition

Natural addition

Amount to be added by

demand

by

husks

of nutrients

means of fertilizer/ash

N 126

13.2

43.3

69.5

P 26

1.83

0.30

23.9

K 202

43.1

95

63.9

Table 8.7 Emission data (kg) for triple superphosphate and potassium chloride (source Simapro 7.1.8 using Ecoinvent 2.0 database)

Emissions

Per kilogram P2O5

Per kilogram K2O

CO2

2.016

0.484

CO2eq

2.064

0.533

NOX

0.0072

0.0016

SO2

0.028

0.0083

recycled to the plantation. The nutrient demand minus the natural addition of nutrients minus the husks gives the amount to be added by fertilization. Further, some natural addition occurs by deposition and transfer. Data from plantations in Cameroon (Hartemink 2005) are used, as data for Cote d’Ivoire were not found in the literature.

The preferred nutrient sources for the nitrogen, phosphorous, and potassium fertilizers for a cacao plantation are urea, triple superphosphate (with 48% P2O5), and potassium chloride (with 49% K2O), respectively (IFA 2008). It is assumed that the fertilizer is produced in Cote d’Ivoire. Data for production in Europe were used, as other data were not available (Table 8.7).

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