The distribution of heavy metals as well as minerals in the fine sand and clay fractions in saprolite derived from coastal plain sands in Southeastern Nigeria were investigated. Heavy metal levels were generally low, when compared to existing permissible standard limits. Ranges for Iron, Manganese, Copper and Zinc were 400-1750 mgkg-1, 51.75-223.75mgkg-1, 12.01-92.75 mgkg-1 and 55-122.1mgkg-1 respectively. Chromium ranged from 1.15-2.53mgkg", Nickel and lead ranged from 0.02-0.08mgkg and0.02-0.25 mgkg-1 respectively. Mineralogical results from the XRD revealed the dominance of quartz, followed by kaolinite with occasional occurrence of illite and wiserite. Trace amounts of Al-Si-Oxide(0.8%) was also found in the fine sand fraction at 18.2-18.9m depth at Uyoafaha. Infrared spectroscopy of the clay fraction also revealed the presence of quartz, kaolinite and lite as well as gibbsite and halloysite.

This study aimed to characterize, classify and evaluate the agricultural potentials of soils formed from the beach ridge sands parent material in the Niger Delta area of Akwa Ibom State, Nigeria. Three toposequences were used as study sites. Along with each toposequence, three profile pits were studied-one at the crest, middle slope and valley bottom. Results of laboratory analysis and fertility capability classification (FCC) showed that the soils were predominantly sandy in texture, strongly acidic (pH 3.3-4.3) and low in the following fertility parameters -organic matter content (1.00-1.28%), total nitrogen (N) (0.043-0.057%), effective cation exchange capacity (ECEC) (2.38-6.02 cmol c kg(-1)), base saturation (56-71%), exchangeable K (0.038-0.090 cmol c kg(-1)) and available phosphorus (P) (4.60-13.12 mgkg(-1)). Based on Soil Taxonomy, soils in the area belonged to two soil orders-Entisols (44.4%) and Inceptisols (55.6%). Also, results of land suitability evaluation (LSE) revealed the land to be marginally suitable (S3) for oil palm, rubber and upland rice cultivation, moderately suitable (S-2) for cocoa and cashew and highly suitable (S1) for coconut cultivation. Major crop production constraints were soil physical characteristics (texture/structure) and fertility. To raise land productivity, management techniques should include application of organic fertilizers to enhance nutrient holding capacity of the soils and supply deficient basic cations. Regular soil testing for proper fertilizer application to ensure a balance nutrient application is also recommended.

Three pedons representing soils on the summit to shoulder (Pedon 1), backslope to footslope (Pedon 2) and toeslope (Pedon 3) positions along a typical hillslope in Afikpo area of Ebonyi State of Nigeria were studied regarding their morphological, physico-chemical and mineralogical properties. The soils were also classified according to the criteria of the USDA Soil Taxonomy and the FAO World Reference Base for Soil Resources. Soils of Pedons 1 & 2 occur on very strongly sloping, severely eroded uplands and are derived from ferruginous, feldspathic sandstone with shale intercalations. The soils in the toeslope position, occur on extensive, nearly level plains which are seasonally waterlogged with colluvio-alluvial sediments constituting the parent material. Irrespective of slope position, all the soils are very strongly acidic with a narrow pH range of 4.6 – 5. 1 and an average exch. Al3+ content of 3.77cmol kg-1 in all the horizons studied. Levels of organic C, total N, avail. P, exch. Ca, Mg, and K, range from being very low in Pedon 1, low to moderate in Pedon 2 but moderate to high in Pedon 3 indicating a gradual improvement in soil fertility from the summit to the toeslope of the hillslope . Kaolinite, mica, quartz, microcline, plagioclase, goethite and gibbsite were detected in the silt fraction of all the soils while kaolinite and poorly ordered illite as well as Fe-rich chlorite dominated the clay mineralogy. According to the criteria of the USDA Soil Taxonomy, the upland soils are Typic Udorthents while the valley bottom soils are Mollic Fluvaquents. In the FAO-WRB system, they qualify as Hper-Dystric Regosols and Mollic Gleysols respectively. Recommendations regarding soil management options have been included. Key words : acid soils, characterization, classification, Entisols, hillslope

Inland valley soils (i.e., valley bottoms and minor flood plains which are seasonally submerged for part or all of the year) are prime soils with problems of less efficient utilization compared to their fertility potentials, and dearth of soil structural information particularly in the tropics. The Cross River State in south-eastern Nigeria has 38 000 ha of inland valleys. A total of six profiles were sampled in this study to evaluate the distribution of soil structural properties with a view to assessing its agricultural implications. Apart from few cases of crumb, angular blocky, and prismatic structures, the surface horizons were principally made of sub-angular blocky structures. The structures of the upper part of the subsoil horizons were a mixture of sub-angular blocky and prismatic whereas that of the lower part was mainly prismatic. Textures ranged from sandy-loam to clay but the latter predominated. The percentage clay increased with increase in soil depth. Particle size distribution showed the soils will be quite suitable for paddy rice production. All the sampled soils had no problems of excessively high bulk densities, hence, would not be expected to impede root penetration and development. The differences in the mean particle density were quite minimal. Particle density was generally less than the average for soils elsewhere, which may be taken as 2.65 g cm(-3).

Six profiles located in the inland valley soils of central Cross River State were studied. The surface horizon colour of the first four were either dark Grey or dark brown. The last two profiles were grey. All subsurface horizons were either greyish or brownish and highly mottled. The structure of all the profiles were either blocky or prismatic with the latter predominating for the subsurface horizons. The textures of the surface horizons ranged from sandy loam to clay while the subsoil soil horizons were predominantly clay. The pH of the soils ranged from acid (4.7). to neutral 7.4 The percent organic carbon content decreased slightly irregularly with increase in depth with the top soils concentration generally high. Similarly, percent total nitrogen was high with most values greater than 0.2%. However, concentration of available phosphorous was moderate. The exchangeable cations Ca. Mg and K were high. Exchange acidity of the soils decreased with increase in profile depth. Cation exchange capacity results were appreciable for four of the six profile with their base saturation values greater than 50% for the surface horizons. Using the criteria of the USDA Soil Taxonomy, profile APT – 1 was classified as Aeric Epiaqulfs, APT – 2 as Typic Epiaqualfs, ABN – 3 as Typic Umbraqualfs and ABN – 4 as Vertic Epiaqualfs. Profiles APP – 5 and APP – 6 were classified as Typic Epiaquults. Using the FAO – UNESCO soil map of the world legend, profiles APT – 1 APT – 2, ABN – 3 and ABN – 4 were classified as Gleyic Luvisols while APP – 5 and APP – 6 as Gleyic Alisols. KEY WORDS: Characterization, classification, inland valley soil, surface horizon, subsoil horizon. Global Journal of Agricultural Sciences Vol.3(1&2) 2004: 25-34

The morphological properties (colour, structure, texture, consistence, miscellaneous features and horizon boundary conditions) of inland valley soils in central Cross River State were described. The soils were sampled from pedogenic horizons and analyzed for physico-chemical properties. They were specially analyzed for pedogenic forms of iron (Fe) and manganese (Mn), namely, acid (pH 3) oxalate extractible and citrate-bicarbonate-dithionite (CBD) extractable forms The soils were deep, gleyed/mottled acid loams and clays, with low (3%) orgaic matter contents. The contents of CBD extractible Fe (FeD) in the surface horizons of soils range from 6255.00 mg kg-1 to 8131 mg kg-1 with a mean of 7100.0 mg kg-1 while the subsoil horizon values range from 5421.0 mg kg-1 to 8131 mg kg-1 with a mean of 6500 mg kg-1. Amorphous iron (Feox) in the surface soil ranged between 959.0 mg kg-1 and 5838 mg kg-1 with a mean of 4000.00 mg kg-1; and the subsoil horizon values ranged from 1084 mg kg-1 to 5838.0 mg kg-1 with a mean of 3500 mg kg-1. Active iron ratio of the surface horizons was in the range of 0.15 and 0.85 with a mean of 0.55. The extractable manganese oxides for the surface horizons ranged between 83.3 mg kg-1 and 550.0 mg kg-1 with a mean of 250.0 mg kg-1 while the subsoil values ranged from 25.0 mg kg-1 to 3392.7 mg kg-1 with a mean of 570.0 mg kg-1. The surface amorphous manganese oxide values ranged from 41.70 mg kg-1 to 325.0 mg kg-1 with a mean of 261.0 mg kg-1. The subsoil results ranged between 20.8 mg kg-1 and 1583.3 mg kg-1 to give a mean of 378.0 mg kg-1. With these concentrations of manganese and iron oxides in these soils, supplemental phosphorus especially after liming during cultivation is recommended for optimum crop yield. Nigerian Journal of Soil Science Vol.4 2003: 41-49

The physical properties of six Inland valley pedons in central Cross River State, Nigeria were investigated. The percent total sand generally decreased with increase in profile depth with the mean total sand for the surface horizons of 47.4% and 37.2% for the subsoil horizons. The mean of percent silt for the surface horizons was 26.9% and 27.2% was that of the subsoil ones while the corresponding values for clay were 25.9% and 38.7%. The percent clay generally increased with increase in profile depth. The surface layers were generally loamy in texture while the subsoil layers were clayey. The mean bulk density of the topsoil horizons was 1.03gcm-3 while that of the subsoil was 1.32gcm-3. Mean particle density of the surface and subsoil horizons were 2.31gcm-3 and 2.29gcm-3 respectively. The mean of total porosity for the surface horizons was 55.1% and that of the subsoil horizons was 32.18%. Soils with these physical properties are very suitable for swamp rice production and dry season farming since their erodibility is low and capillarity high. Keywords: Physical properties, surface soil, subsoil horizon, porosity, texture. [Global Jnl Agric Res Vol.2(1) 2003: 37-42]

The dispersion of sesquioxide-rich or plinthitic soils is difficult and not completely achieved within routine dispersion period. Two prolonged shaking periods of 24 and 48 hours were tested to see which gives a more complete dispersion of two plinthtic soils-a drier Plinthustalf and a more humid Plinthustult. Iron oxides which are the main aggregating agents in plinthite were also determined and the iron ratios calculated to relate their contents to the rate of dispersion of the soils. Results showed that prolonged shaking for 24 hours gave greater dispersion which changed the textural classification of the soils from the routine time (5 minutes shaking) to finer textural classes. Shaking for 48 hours increased the clay content significantly (P = 0.001) over that of the 24 hours but textural classification did not change further. The soil clay was aggregated mainly into silt-size particles as the clay content increased at the expense of the silt fraction on prolonged dispersion period. Both the amorphous and crystalline inorganic iron (Fe) oxides were responsible for aggregation in the soils. and their effects were enhanced by desiccation. Dispersion was therefore more difficult in the drier Plinthustalf than in the more humid Plinthustult.

Abstract The contents and pedogenetic distribution of pyrophosphate, oxalate, and dithionite extractable iron oxides were examined in three Ultisois and an Alfisol developed on older granites. The soils represented a bio‐climatic sequence in Nigeria, the Sudan, Northern Guinea, and Southern Guinea savannas and the Rainforest zones. Pyrophosphate extractable iron (Fe) in the soils rangfid from 0.14 to 0.69%, oxalate extractable iron (Feox) ranged from 0.03 to 0.36%, whereas the dithionite extractable form (total free iron oxides) varied from 0.50 to 8.00%. The contents of pyrophosphate and oxalate extractable Fe, i.e., the amorphous forms were low and represented only 0.9 to 28% and 5 to 6%, respectively, of total free iron oxides. The soil in the more humid rainforest contained the highest amounts of all forms of free Fe oxides. In the savanna soils the contents of free iron oxides decreased in the order Northern Guinea > Sudan > Southern Guinea. Pyrophosphate and oxalate extractable Fe increased slightly...

Three pedons developed on basaltic parent materials on the Biu Plateau in the semi-arid region of Nigeria were characterized and classified. Soil pH values ranged from 6·0 to 6·6 and increased slightly with increase in profile depth. The clay content was generally above 40% and the slit fraction ranged from 20 to 34%. Exchangeable bases were high and values for exchangeable acidity did not exceed 0·20cmol(+) kg−1. The NH4OAc-CEC, effective CEC, and base saturation (NH4OAc-CEC) were moderately high, while base saturation by effective CEC method was high with all values above 90%. Organic C content of the surface soils was medium, but the soils were deficient in N, P and S. The pedons were classified as Typic Haplustalfs (Haplic Alisol and Chromic Luvisol) and as Ustic Dystropept (Chromic Cambisol). The agricultural potentials of the soils were considered to be favourable, although constrained by N, P and S deficiencies.

The profile distribution of total, diethylene triamine penta-acetic acid (DTPA)- and 0·1mHCl-extractable Fe and Mn were determined in 12 pedons formed on three contiguous sand dunes in the semi-arid savanna of Nigeria. The total Fe and Mn contents varied from 100 to 3750 and 40 to 11,375μgg−1, respectively. Values of 0·1mHCl-extractable Fe and Mn varied from 8·0 to 123 and 1·5 to 43·5μgg−1, respectively. The corresponding values of DTPA-extractable Fe and Mn were 4·5 to 16·0 and 1·0 to 38·8μgg−1. Total Fe and Mn correlated significantly with clay in nearly all the dunes (p≤ 0·01) but were not significantly correlated with organic matter. The 0·1mHCl-extractable Mn had a positive significant correlation with soil pH (r= 0·58*) in Illela dunes but a negative significant correlation with pH in the Sangiwa dunes (r= −0·75***). The values of extractable Fe and Mn in the sand dune soils are above the critical limits reported in other literature, thus deficiencies of these micronutrients do not pose a problem to crop production in the study area.

The available (0.1M HCl- and DTPA-extractable) and total forms of copper (Cu) and zinc (Zn) were determined in soils developed on various groups of basalts, namely, the Newer, Older, Lateritized-Older, and Bin (undifferentiated) basalts. The HCl-, DTPA-extractable, and total Cu in the soils ranged from 0.40 to 5.60, 0.15 to 2.64, and 15 to 65 mg On kg(-1), respectively, with corresponding means values of 2.06, 0.89, and 41 mg Cu kg(-1). Similarly, HCl-, DTPA-extractable, and total Zn varied from 3.00 to 6.20, 0.14 to 2.15, and 25 to 265 mg Zn kg(-1) with respective mean values of 4.65, 0.52, and 89 mg Zn kg(-1). The soils were high in the total forms of On and Zn, generally sufficient in available Cu, but deficient in available Zn. Both the total and available forms of Cu and Zn were little correlated with soil properties in soils of the Lateritized-Older and Bin basalts, while only the available forms were related mainly to silt, clay, pH, and organic carbon in soils of the Newer and Older basalts. Furthermore, the available forms were correlated with each other, but not with the total forms.

Sulphate adsorption and desorption characteristics of three Ultisols and an Alfisol developed on basaltic parent materials in the Nigerian savanna were investigated. All the soils exhibited high Q (quantity) or adsorption capacities for low levels of added sulphate (30 to 60 mu g S g(-3) soil) at all levels of added sulphate. The Q/I curves closely fit the Freundlich but not the linear form of the Langmuir equation. The Ultisols adsorbed similar amounts of sulphate which were all significantly higher than that adsorbed by the Alfisol (P = 0.01). Sulphate adsorption in the soils was not significantly related to clay content, but was negatively correlated with soil pH (r = -0.77*) and positively correlated with dithionite extractable iron (r = 0.813*) and oxalate extractable aluminium (r = 0.863**). The amounts of sulphate desorbed from the Ultisols were also similar and significantly higher than that desorbed from the Alfisol (P = 0.05). Sulphate desorption was not significantly related to soil pH, clay content or Fe and Al oxides but was negatively correlated with organic carbon (r = -0.899**) and available sulphur (r = 0.770*). About 77 to 89% of initially adsorbed sulphate in surface soils and 36 to 72% in subsoils were not recovered by three sequential extractions with a 500 mu g P cm(-3) solution and between 78 and 100% of the total amounts of sulphate desorbed was removed by the first extraction with the P solution.

Soils representative of the stabilised Illela sand dunes in northwestern Nigeria were examined in the field and additional properties of four pedons determined in the laboratory. The soils are deep, dark-brown and sandy throughout their profile. Organic carbon contents are very low, less than 2 g kg(-1), and with the siliceous parent material the consequence is low amounts of available nutrients, particularly Ca, K, Mg and N. However, P is moderate to high due to the occurrence of phosphatic nodules at depth. Available micronutrients, Cu, Zn, Mn and Fe, are generally above the critical limits and are adequate for most crops. The high bulk density and low porosity constituted largely of macroporosity impart low water-holding capacity to the soils. Quartz is the dominant mineral in the sand and silt fractions while kaolinite dominates the clay fraction of the soils. According to the USDA Soil Taxonomy and FAO/UNESCO systems of soil classification, all pedons are classified as Ustic Quartzipsamments or Ferralic Arenosols, except four pedon 2 which is classified as Arenic Haplustult or Haplic Acrisol. From the general characteristics of the soils, it is recommended that proper organic matter management via the incorporation of crop residues into the soil, the use of organic manure and crop rotation involving legumes, will greatly enhance the productivity of the soils.

The contents of 0.1M HCl and DTPA extractable and total iron (Fe) and manganese (Mn) were determined in soil profiles developed on four groups of basaltic parent materials, namely, the Newer-, Older-, Lateritized-Older-, and Biu-basalts. HCl- and DTPA-extractable and total Fe in the soils ranged from 15.0 to 66.3 mg/kg, 1.1 to 26.7 mg/kg, and 4.50 to 10.50%, respectively, with corresponding means of 37.5 mg/kg, 9.5 mg/kg, and 7.33%. The corresponding forms of Mn ranged from 1.1 to 89.0 (mean, 39.8) mg/kg, 0.3 to 114.7 (mean, 24.3) mg/kg and 34 to 1010 (mean, 346) mg/kg, respectively. The soils were high in total Fe and Mn and sufficient in the available forms (HCl- and DTPA-extractable forms). Total Fe and Mn were neither related to the available forms or to soil properties tested. The available forms were, however, related one with another and largely associated with organic matter.