1. INTRODUCTION
Oil palm (Elaeis guinensis ) is one of the plantation crops grown in some tropical countries of the world especially Nigeria in addition to cocoa, kola, teak, gmelina, rubber, and cashew as a result of transformations in agriculture. It is cultivated mostly in the southern, eastern, and western parts of the country. Recently, planted areas had increased at a rapid pace, and the increase is significantly evident. Oil palm was adopted and cultivated among the high-value perennial tree crops by individual small-scale growers, private agencies, and government agencies (state and federal). Global oil palm production is approximately 272,055,131 tonnes from 18,917,400 hectares, with Asia (84.1%) taking the lead, followed by Africa (9%) (FAO, 2020). It is a major source of oils and fats for human food, livestock feed, and manufacturing of several other domestic products, such as cosmetics, soap, and detergents (Reiger, 2006).
The increase in oil palm demand has resulted in the conversion of natural vegetation into oil palm plantations. The conversion of some rainforests and the use of abandoned logged-off forests into oil palm plantations is expected to have contributed significantly to nutrient losses from both soil and vegetation (Brahene et al., 2016; Rozieta et al., 2016). Deforestation and loss of habitat of critically endangered species (Clay, 2004), a decrease in soil productivity, an increase in soil erosion, and soil biodiversity loss (Comte et al., 2012; Savilaakso et al., 2014), and a substantial increase in greenhouse gas emissions are the detrimental effects of oil palm on the climate (Bates et al., 2008; Hassan et al., 2011). Rising tillage intensity and the conversion of the natural environment to agricultural land have contributed to a decline in soil organic matter levels due to decreased organic carbon inputs and decreased physical conservation of soil organic carbon contents (Chibsa and Ta’a, 2009).
As a consequence of the combined effects of physical, chemical, and/or biological processes operating at various intensities and on different scales, the classification of soils depends on the degree of spatial heterogeneity (Priyabrata et al., 2008). Research has shown that crop age also leads to soil variability because nutrients are extracted from the soil during harvest for grain, fiber, wood, and crop residues as the crops grow older (Basiron, and Weng, 2004; Aweto and Enaruvbe, 2010). If replenishment with inorganic and/or organic fertilizers is insufficient, nutrient removal can result in a decrease in soil fertility (Okon et al., 2017). There seems to be little or no knowledge as touching the impact of oil palm plantations of different ages on soil physico-chemical properties in the research region to date on various studies on oil palm plantations in Nigeria. Therefore, it is of great importance to assess the quality of soil nutrients in existing oil palm plantations of various maturity ages and to analyze the variability (differences) in the soil properties of these oil palm plantations.