Chapter 2: Research Methodology
2.5 Developing Allometric Equations for Date Palm
2.5.2 Field Measurements
A fieldwork campaign was conducted during the fourth week of April 2018 where five DP were uprooted for each age stage (total of 15 palms). Each sampled palm was partitioned into three parts: crown, trunk and roots (Khalid et al., 1999a).
The term biomass, in this research, refers to the value of dry weight unless indicated otherwise. Although some researchers prefer to use the fresh weight instead of dry weight for building their equations (Dewi et al., 2009; Khalid et al., 1999a) (Appendix 1). Hence, AGB is calculated as the sum of the crown and trunk weight while BGB is calculated as the weight of the root system. A large commercial scale balance was used to get the fresh weight of crown, trunk and roots in (Kg). From each part of the
uprooted palms, three samples were collected (3 crown samples, 3 trunk samples and 3 root samples), (Figure 13).
Figure 13: Uprooting, partitioning, and weighing date palms. After (Salem Issa et al., 2018, 2020b).
Structural variables of uprooted DP including total palm height, trunk height, diameter breast height (DBH), crown diameter (CD), crown area (CA) and number of fronds (#Frond), were measured and later used in the regression analysis to build specific biomass allometric equations of date palm. Before uprooting the palm, the following variables were measured: (i) DBH in cm by measuring the circumferences of the trunk at 1.3 m height and dividing by the number π. For small palms, with no developed trunk, the diameter was measured at the base of the palm, (ii) Number of palm fronds (#Frond), (iii) CD in meter, and (iv) CA in square meter was calculated using the sphere equation (CA = π CD2/4), assuming a rounded palm crown. After uprooting the palm, the following variables were measured: (i) Palm height (H) in meter, (ii) Palm trunk height (Ht) in meter, and (iii) Crown depth (Δheight), defined as the difference between total and trunk heights in meter.
2.5.3 Biomass and Soil Samples Processing for Measuring Palm Biomass and Carbon Contents
A total of 120 biomass samples were collected during the fieldwork: (15 Crown + 10 Trunk + 15 Root) x 3 replicates. Only 10 x 3 trunk samples were collected due to the absence of developed trunk in young palms. Four soil samples were collected from underneath each palm canopy, referred to as “In”. A total of 60 soil samples: 15 palms x 4 replicates were collected during the campaign. More soil samples were collected away from the palms’ canopy, referred to as “Out”, from two DP farms: [2 farms x 4 replicates], for comparison and quantification of the effect of DP contribution to soil carbon sequestration. Immediately after reaching the UAEU/ Biology department’s Labs, the fresh weights of all samples were measured. Then, samples were air dried and transferred to paper bags to be ready for oven drying at 80℃ for 72-96 hours to measure the dry weight (Allen et al., 1974; Corley et al., 1971; Khalid et al., 1999a).
Samples were prepared and grinded to calculate the biomass components’ parameters using the formula listed in Table 4. Samples were weighted to get the percentage of dry weight to original fresh weight in each sample (dry to fresh factor=DF) (Figure 14). Finally, samples were combusted for 4 hours at 550℃ (Allen et al., 1974)) to calculate organic matter (OM) and organic carbon (OC) as per the formula in Table 5.
Table 4: Calculation of different date palms biomass components.
Parameter Formula
Dry Weight of each
palm part (Kg) Crown Dry Weight = Crown Fresh Weight × Crown DF*
Trunk Dry Weight = Trunk Fresh Weight × Trunk DF Root Dry Weight = Root Fresh Weight × Root DF Percentage of BGB
(Root system) from the AGB**
BGB:AGB ratio = BGB/AGB × 100
AGB weight in each
palm (Kg) AGB = Crown Dry Weight + Trunk Dry Weight Total Biomass of each
palm Total Biomass = AGB Weight + Root biomass Weight (BGB)
*DF is dry to fresh factor
** The ratio of each biomass component (crown, trunk, and roots) to the total biomass were calculated as well.
Table 5: Calculation of OM and OC of the collected samples.
Item Formula
The percentage of OM to dry weight in each sample
%OMD* = (1- Combustion Weight 550℃ /Dry Weight 80℃)
× 100 The OM Weight for
palm parts in each palm (Kg)
Crown OM Weight = Crown Dry Weight × % Crown OMD Trunk OM Weight = Trunk Dry Weight × % Trunk OMD Root OM Weight = Root Dry Weight × % Root OMD The OC weight
palm parts in each palm (Kg)**
Crown OC Weight = Crown OM Weight × 0.58 Trunk OC Weight = Trunk OM Weight × 0.58 Root OC Weight = Root OM Weight × 0.58 The OC in AGB for
each palm (Kg) OC in AGB = Crown OC Weight + Trunk OC Weight Total OC in each
palm Total OC = OC in AGB + OC in Root biomass
* OMD is OM to dry factor
** OC is equal OM multiply by 0.58
Figure 14: Lab works, preparing samples, grinding, weighing, and drying.
Soil samples were first air dried and prepared for further processing (Allen et al., 1974). They were then placed in crucibles and oven-dried at 105℃ for 72 hours.
The different soil samples’ parameters were calculated using formulae listed in Table 6 following the approach described in (Ksiksi, 2012; Lemenih & Itanna, 2004).
Table 6: Formulae used to calculate the different soil parameters.
Item Formula
% Moisture
content = (Initial Weight–Dry Weight 105℃)/Initial Weight × 100 Bulk density
(g/𝑐𝑚3) = dried-oven Weight (g)/ Total volume of the sample
% SOM* = (Dry Weight 105℃ – Loss of Combustion)/ Dry Weight 105℃
× 100
% OC** = OM x 0.58 Soil carbon
(g/𝑚2)*** = Z x BD × C × 10 Soil carbon in
Kg/palm = (Soil C. (g/𝑚2) × CA) / 1000
* Combustion was performed for 4 hours at 550℃ to estimate %SOM
**% OC is estimated as 0.58 of the calculated OM
*** Where Z = thickness of each sample depth (10 cm), BD = bulk density (1.7 g/𝑐𝑚3) of each sample depth and C is the carbon concentration (g.C/Kg soil) of each sample depth. Results are reported in tons per hectare.
The total CS in and contributed by the DP is calculated as the sum of CS in the DP biomass itself plus the CS in the soil underneath the palm as explained and formulated as per equation 1 below:
Total CS = Biomass C + Soil C Eq. (1)