Deterioration of soil physical properties and organic matter depletion resulting from continuous cultivation of tropical sandy loam soils, even with the regular applications of inorganic fertilizers is common. To regenerate the soil organic matter and maintain soil structural and hydraulic properties for crop production, the effects of different legumes green manures and NPK chemical fertilizer were evaluated after a 3-year field experiments at the University of Port Harcourt, Teaching and Research Farm (2018 – 2021). Treatments were: 5 tons ha-1Centrocema (Ce5), 5 tons ha-1 Gliricidia (Gl5), 5 tons ha-1Calapogonium (Ca5), NPK 20:10:10 (NPK) and the Control, arranged in a Randomized Complete Block Design (RCBD), in 5 replications. Results showed that three annual applications of  Centrocema, Gliricidia, and Calapogonium  increased  soil organic carbon pool at the 0-30 cm topsoil, and reduced the bulk densities by 8.5%, 4.1%, and 7.0%, respectively, compared to the NPK fertilizer and control. The increased in bulk density in untreated  plots led to decrease in water stable aggregates, low water holding capacity and low yield of cucumber crop. Green manures applications increased soil organic carbon pool, improved topsoil physical properties and cucumber yield, while NPK chemical fertilizer had negative effects on these properties.

Evaluation of carbon stock in soil is an essential step in estimating the carbon storage potential of an ecosystem. A field study was carried out on a humid tropical Rainforest and Mangrove soils at the Forestry Unit of the Rivers State University Teaching and Research Farm and the Eagle Island quantify the effects of vegetation and seasons on soil organic carbon, organic carbon stock and other physical to attributes of the soils. Results revealed that seasons and vegetation did no change the soil texture, but influenced other properties of the soils. Bulk density was significantly low (p<0.05) at 0.64 g cm-3 in Mangrove soils in the peak of dry season. Saturated hydraulic conductivity (Ksat) was moderately rapid (20.88 cm h-1) in Rainforest soil, and moderately slow (15.59 cm h-1) in the Mangrove soils. Soil organic carbon (SOC) was significantly higher (p<0-05) in mangrove soils at 53 g kg-1 during the rains, and 16 g kg-1 in Rainforest soils during the same season. Soil organic carbon stock (SOCS) was significantly higher at 65.4 kg m-2 in Rainforest soils (p<0.05), compared to 8.4 kg m-2 in Mangrove soils during the same season. SOCS correlated positively bulk density (BD) (r = 0.679, p<0.05) and clay content (r = 0.892, p<0.01). The model: Y = 0.165+4.068x can be used to predict SOCS and bulk density, also the model Y = -0.246+0.361x can be used to predict the effects of clay content on SOCS in the two soils during the seasons. The Rainforest was found to have the potentials to store carbon in the soil than the Mangrove.

Crude oil contamination in the Niger Delta has become a serious problem for soil health and agricultural production. We hypothesized that applying Trinervitermes spp of termite soil and introducing the Blue porter plant (Stachytarpheta jamaicensis) to crude oil contaminated soil can accelerate microbial activities and improve the soil's physical properties and organic matter content. A field experiment was carried out on a 0.02 ha land to assess the effects of Trinervitermes geminatus termite soil and Stachytarpheta jamaicensis plant on the physical properties of a sandy loam soil contaminated with crude oil in the Niger Delta of Nigeria. The experiment was arranged in a Randomized Complete Block Design (RCBD), consisting of 13 treatments in 3 replications. The soil was contaminated with 4% crude oil (equivalent of 40,000 mg kg-1) (Cr4) and 5% crude oil (equivalent of 50,000 mg kg-1) (Cr5), in single application. The soil was treated with 10 and 20 t ha-1 of Trinervitermes geminatus termite soil (10Mo and 20Mo, respectively), alone and in combination with Blue porter plant (Stachytarpheta jamaicensis). Results revealed that 6-month applications of Trinervitermes geminatus termite soil and Stachytarpheta jamaicensis plant have significant effects on physical properties and Soil Organic Matter SOM) Applying 10 and 20 t ha-1 of termite soil in combination with Stachytarpheta jamaicensis plant to 4% crude oil increased SOM from 29 g kg-1 in the control plots to about 61 g kg-1 after 6 months. The application of 20 t ha-1 termite soil to 4% crude oil (Cr4+20Mo) reduced soil bulk density, increased saturation water content by 15%, and saturated hydraulic conductivity (Ksat) from zero to 1.67 and 1.53 cm h-1 in 6 months, after the application compared to the untreated Cr4 soil. Macro-aggregates > 0.25 mm were generally higher in the termite soil alone and in combination with the Blue porter plant. Micro-aggregates <0.25 mm dominated the Control plot (54 and 46% after 3 and6 months). Water stable aggregates in 4.75-2.0 mm size class increased from 22% to 56% for Cr5+20mo after 6 months. The termite soil improved the macro-aggregates, while the Blue porter plants improved Ksat of the soil after 6 months.