Dynamics Of Soil Carbon Sequestration Under Oil Palm Plantations Of Different Ages

ABSTRACT

It has been estimated that globally a lot of forest is lost in the tropics annually to agriculture. The

removal of the forest cover has been cited as one of the main contributors of greenhouse gases.

Tree plantations are advocated as carbon (C) sink, however, little is known about rates of C

turnover and sequestration into soil organic matter under tropical tree plantations particularly oil

palm. One of the commonest management practices adopted by farmers on oil palm plantations

involves the prunning of the palm branches and heaping them in between the palm trees in the

rows. The spaces or the alleys between the palm trees contained no heaped branch residues. So

far very few studies have been conducted to assess the contributions of pruned branches heaped

at the different locations under the palm plantations to the fertility status of the soil. The

objective of this research was to assess the dynamics of soil C sequestration under oil palm

(Elaeis guineensis) plantations at different ages in a semi deciduous forest zone of Ghana. A

diagnostic field study was carried out to identify oil palm plantations at different ages occurring

within the Kwaebibirem District, Ghana. The oil palm plantations were categorised into five age

groups (0-5, 5-10, 10-15, 15-20 and 20-25 years). A forest reserve which had not been cultivated

for more than 50 years served as a control. All the cultivated farms and the control plot were

located at the valley bottom slope on Oda soil series (Aeric Endoaquent). Soil samples were

collected under the heaped branches and from the spaces between the palm trees at a depth of 0-

10 and 10-20 cm respectively. The control soil from uncultivated plot was also taken at the same

depth. The soil samples were collected for bulk density (BD) and organic C determinations.

Carbon stocks were calculated using measured C content and the corresponding soil bulk

densities. The presence of the residue resulted in lower BD values under heaps than those under

alleys with age irrespective of the depth. The OC in the soil decreased with cultivation but was

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drastic after 5 years of plantation establishment up to age 20 years in both layers under heaps

with losses accounting for between 13-45% of the control. In the alleys the OC losses were

greater with age in both depths with the lower layer having OC deficit of 57%. The conversion of

the forest into the oil palm plantation led to a dramatic loss in soil C stocks of around 45% in the

top 10cm irrespective of heap or alley location. In the 10-20cm layer loss was 50-60% with

lower decline under residue heaps. Under heaps significant improvements in the C stocks in the

top layer is discernible after 20 years but not in the alleys. The carbon saturation deficit followed

a similar trend as the C stocks. The conclusion from this study is that oil palm plantations have

the ability to sequester carbon over a period of time when palm fronds are added to the soil.