4. DISCUSSION
The physical and chemical properties of the soil in different land use
may be attributed to differences in the study area’s management
practices. Soil texture is an inherent property; spatial variations
between soils with less variation associated with cultivation could be
due to the textural differences found (Brahene et al., 2016). In the
0-20 cm layer, soil bulk density values were comparatively lower when
compared to those of 20-40 cm layer where the content of organic matter
was very low. This suggests that OM has contributed significantly in
enhancing the soil’s physical properties, thereby contributing to the
soil’s structural stability (Germer and Sauerborn, 2008). The BD values
obtained cannot hinder root development and penetration.
The low pH of the soils can be attributed to the nature of the parent
materials and the high precipitation that causes the basic cations in
the soil to leach intensively (Tweneboah, 2000; Owusu-Bennoah et al.,
2000, Oyegoke et al., 2017). Low pH values connote the presence of a
positively charged colloidal surface capable of attracting negatively
charged ions. The values for oil palm production, however, were
acceptable because they were below 7.5 and did not favor oil palm
production above that value (Okon et al., 2017). Available soil
phosphorus level was low, as the values were between 3-7 mg/kg (Federal
Fertilizer Department, 2012). This means that the amount of phosphorous
is according to the pH status of the oil palm plantations. In this
land-use system, the higher available P content within the forest may be
correlated with an increase in microbial activity.
The high OC content of soils under heaped fronds is related to the
quantity, position, consistency, and temperature and humidity actions on
the pruned fronds compared to those under alleys (Kirschbaum, 2000;
Comte et al., 2012). As a result of the rapid decomposition of palm
fronds, there could be a rise in OC and soil nutrients in planting for
less than 10 years, but as the planting age moved to 25 years, the
decomposition rate slowed down with decomposed material being covered by
overlying palm fronds (Okon et al., 2017). Thus, with the age of the
plantation, it is possible to find heaps of different heights (Brahene
et al., 2016). Total nitrogen (TN) varies with the quantity of organic
matter present in soils, so it has risen without exception, along with
improvements in the related status of organic matter. Relatively, TN
amount is also determined by organic carbon, which in turn results from
plant and root biomass, as well as residues returned to the soil system.
The key cause of N deficiency in tropical soils is extreme leaching and
erosion due to high tropical precipitation (Aweto and Enaruvbe, 2010;
Osinuga and Oyegoke, 2019).
The low level of basic cations in the plantations results from the
effect over time of the continuous uptake of nutrients by the plants.
The result shows that the intensity of weathering, cultivation, and use
of inorganic acid-forming fertilizers affects the distribution of the
cations in the soil system and improves their depletion (Owusu-Bennoah
et al., 2000). The low values observed for these basic cations may also
be due to the low content of organic matter and the presence of low
activity clays of the area (Oyegoke, 2011). Subsequently, the obtained
CEC is a function of the pH and SOM in the soil and, with the age of the
oil palms, the value remained reasonably constant in the soil. This is
an indication that the soils remain low in CEC at their natural pH
levels, demonstrating the soils’ low nutrient retention ability.