Ayodele Olumide Adelana

Evaluation of two methods of soil quality assessment as influenced by slash and burn in tropical rainforest ecology of Nigeria

The sustainability of slash-and-burn agriculture for sustainable crop production has been a subject of controversy. The objective of this study was to quantify the effect of slash and burn on soil quality. Two sites, Ibadan (7° 23′ N; 3° 51′ E) and Akure (7° 17′ N; 5° 14′ E), within the tropical rainforest of Nigeria were selected for the study. Burnt and unburnt soils were cropped with maize, melon, and cowpea (in sole and intercrops). Soil and earthworm cast samples were collected and analyzed for physical, chemical, and biological indicators. Integration into soil processes and quality indices involved the transformation of analyzed indicators using Soil Management Assessment Framework (SMAF) and Multiple Variable Indicator Transform (MVIT) techniques. Organic matter, water-stable aggregates, pH, cation exchange capacity, macroporosity, and water infiltration were reduced after burning in both sites. Active carbon and potentially mineralizable nitrogen increased after burning at Ibadan but decreased after burning at Akure. Soil quality decreased after burning by a range of 11.3–24.8% using SMAF and MVIT, respectively, although only MVIT showed significant differences (p ≤ 0.05). Test crops increased in yields on burnt soils due to prompt release of nutrients to the crops; the benefit was dwarfed by the adverse effects of burning on soil quality indices.

Conservation Strategies for Effective Management of Eroded Landform: Soil Structural Quality, Nutrient Enrichment Ratio, and Runoff Water Quality

Water erosion remains a major threat to soil and water conservation in the humid tropics and, thus, requires effective conservation measures to curb it. To quantify the efficacy of vetiver grass (Chrysopogon zizanioides L.) strips and mulch in soil structural quality buildup and in reducing the eutrophic quality index and enrichments ratios of major nutrients, a study was conducted between 2007 and 2009 on eroded landform (8% slope) of a Typic Kanhapludalf in a subhumid region of southwestern Nigeria. Treatments were vetiver buffer strips (10 m vetiver grass strip [VGS]), vetiver mulch (6 Mg ha−1 vetiver grass mulch [VGM]), combined vetiver strips and mulch (10 m VGS + 4 Mg ha−1VGM), and a control (no buffer strips or mulch). Soil structural quality estimated by water-stable aggregates at 0- to 5-cm depth increased by 36%, 73%, and 64% under 10 m VGS, 6 Mg ha−1 VGM, and 10 m VGS + 4 Mg ha−1 VGM, respectively, more than the control. The corresponding increase in mean weight-diameter under the vetiver systems was 30%, 42%, and 47% higher than the control. The water-stable aggregates and mean weight-diameter at the 5- to 15-cm depth followed a similar trend in the 0- to 5-cm layer. The resistive potentials of the vetiver systems in reducing soil loss, sediment-associated nutrients, total suspended solids, and eutrophic quality index were significantly higher than the control because of an increase in surface hydraulic roughness, which were in the order of 6 Mg ha−1 VGM < 10 m VGS < 10 m VGS + 4 Mg ha−1 VGM. Application of 6 Mg ha−1 VGM appear to be better than 10 m VGS and contributed to the reduction of runoff and enrichment ratios, thus, changing the order to 10 m VGS < 6 Mg ha−1 VGM < 10 m VGS + 4 Mg ha−1 VGM. The results indicate that an integration of vetiver buffer strips and mulch (10 m VGS + 4 Mg ha−1 VGM) had a better control of runoff, soil loss, sediment-associated nutrients, and water quality degradation, as well as improving soil structural quality buildup when compared with vetiver buffer strips or mulch alone.

Comparative Effects of Vetiver Grass (Chrysopogon zizanioides) Strips, Vetiver Mulch and Veticompost on Soil Quality and Erodibility of a Sloping Land

Abstract This study investigates the influence of vetiver grass strips (VGS), vetiver mulch (VGM) and composted vetiver prunes (veticompost) on soil quality of an eroded land in the Institute of Agricultural Research and Training, Ibadan (70 22’ N; 30 50’E), Nigeria. The treatments were 3-m wide VGS established at 10-m inter-row spacing, VGM imposed at 5 Mg ha-1, veticompost applied at 5 Mg ha-1 and a control (no-vetiver grass). All quality indicators including physical, chemical and biological indices and soil erodibility (K) factors were determined between 2008 and 2011. Results show that soil organic matter (SOM) and associated nutrients play a major role in soil quality variation. VGM had the highest impact on soil quality (76.5%) but not significantly different (P<0.05) from veticompost (72.5%). Soil quality ratings were in the order of VGM > veticompost > VGS > control. Significant and positive relationship (r = 0.92*) exist between soil quality ratings and maize yield, with 70% of grain yield variability accounted to the soil quality. K factor ranged from 0.013 to 0.030 Mg h MJ-1 mm-1 with the VGM and control plots having the least and highest K factors, respectively. Although the soil quality under veticompost is lower than vetiver mulch but the SOM and associated nutrients under veticompost enhanced better soil productivity, and thus accounted for higher crop yields than other treatments.

Assessment of spatial variability and mapping of soil properties for sustainable agricultural production using geographic information system techniques (GIS)

Abstract Mapping of soil properties is an important operation as it plays an important role in the knowledge about soil properties and how it can be used sustainably. The study was carried out in a local government area in Oyo state in order to map out some soil characteristics and assess their variability within the area. Soil sampling was carried out in three different locations in the local government area using the cluster sampling technique. Ten samples were collected in each location within a 10 by 10 km area, soil was sampled at two depths (0–20 and 20–40 cm) respectively. The soil samples were air-dried, crushed and passed through a 2 mm sieve before analyzing it for Nitrogen, phosphorus, Potassium, Organic carbon, pH and exchangeable bases in the laboratory while the SAR, ESP% and cation exchange capacity (CEC) were calculated. After the normalization of data classical statistics was used to describe the soil properties and geo-statistical analysis was used to illustrate the spatial variability of the soil properties by using kriging interpolation techniques in a GIS environment. Results showed that the soil properties with high variability in terms of coefficient of variation are available phosphorus and potassium (C.V = >35%), nitrogen, CEC, OC, SAR and ESP were all moderately variable (C.V = 34–15%) while pH had low variability (C.V = <15%). These variations in chemical properties are mostly related to the different soil management practices carried out in the study area and the parent material on which the soil is formed.

Distributions of cadmium and lead in peri-urban wetlands as influenced by soil organic matter, clay fraction, and moisture content

Abstract Environmental distribution of cadmium (Cd) and lead (Pb) were studied in two wetlands (alluvial plain and inland depression) in Ibadan, Nigeria. Mean and median values of variables measured across the wetlands showed that soil properties varied considerably. Hydraulic conditions, soil organic matter (SOM), and particle size distribution contributed to the distribution of heavy metals recorded. Profile distribution of Cd and Pb maintained two patterns: (1) linear distribution pattern, where concentrations of Cd and Pb increase and decrease respectively, with increase in soil depth and (2) middle depth enrichment. Active carbon (AC), SOM, and clay fraction affected the surface and profile distribution of Cd and Pb. Cadmium showed significant correlation (R2 = −0.61* and 0.64*) with AC and SOM, respectively, while Pb had R2 values of 0.77* and 0.57 with SOM and clay content, respectively. The non-residual fractions of the heavy metals increased with increasing metal loading and SOM. This study is useful in assessing chemical changes for Cd and Pb in different wetlands, and their potential release to the environment.