Growth and yield of groundnut (Arachnis hypogeal) in bituminous soils of Southern Ondo State, Nigeria

Several studies have been conducted on the physio-chemical and heavy metals characterization of a bituminous soil, but very few studies have investigated the potential of cultivating an economical like groundnut in such soil. Therefore, this study investigated the potential of cultivating groundnut in bituminous soils with the aim of determining; (i) the effects of soil nutrients and heavy metals on the growth and yield of groundnut; and (ii) the main and interactive effects between locations with varying bitumen contents and soil depth on the heavy metals. Three different locations (Loda, Lofo, and Legbogbo sites) were considered for the research. Loda and Lofo are bituminous soils, while Legbogbo is bitumen free. Soil samples were collected at interval of 10 cm depth up to 100 cm during two growing seasons and taken to the laboratory for physico-chemical and heavy metal tests. During the growing seasons, the plant height, number of leaves were measured. Significant difference (P < 0.05) in the growth parameters were observed among the locations (Loda, Lofo, and Legbogbo) where the crop was planted in both seasons. It was observed that there was an increasing trend for the agronomic measurement in all locations and seasons were in the order of Legbogbo > Lofo > Loda in most cases on function of weeks after planting (WAP). Also, significant (P < 0.05) effects of the location were recorded on the groundnut components, due to the level of bitumen present in the soil. For the year 2020 growing season, weight of the groundnut pod ranged between average value of 4.27 and 29.53 g at Loda and Legbogbo, while it similarly ranged between 8.08 and 59.87 g at Loda and Legbogbo for the year 2021 growing season. Significant main and interactive effects were observed in the bituminous soil on the soil nutrients and heavy metals, thus further explaining the markedly differential groundnut productivity. Using the stepwise regression model, analysis of results showed that the soil potassium and phosphorus are important for the cultivation of groundnut. Therefore, cultivation of groundnut in a bituminous soil is possible with the presence of increased potassium and phosphorus contents.