Nigerian Soils Research Articles

Degradation and sorption of pirimiphos-methyl in two Nigerian soils.

This research is a continuation of a study on the behavior of hydrophobic organic compounds in the environment and describes the simultaneous abiotic degradation and sorption of pirimiphos-methyl (O-2-diethylamino-6-methylpyrimidin-4-yl O,O-dimethylphosphorothioate) under controlled conditions in soil/water slurries. A microfiltration-HPLC technique was employed to follow these processes in two well-characterized soils from the Middle Belt region of Nigeria. Rapid sorption of the pesticide occurs during the first 10 min of equilibration and accounted for 37% of the original pirimiphos-methyl in the Rhodic Kandiustalf soil and for 41% of the original concentration in Aquic Ustropept soil. Subsequent slow processes were followed during the remaining 30 days of the experiment. During this time, first-order rate constants for disappearance from solution of pirimiphos-methyl were found to have values of 6.1 x 10(-)(7) and 9.8 x 10(-)(7) s(-)(1) for the Rhodic and Aquic soils, respectively. Similarly, rate constants for production of the product, pyrimidinol, were calculated to be 6.0 x 10(-)(7) and 9.4 x 10(-)(7) s(-)(1) for the Rhodic and Aquic soils, respectively, giving pesticide degradation half-lives of 13 and 8.5 days. Disappearance of the pesticide is discussed in terms of a scheme involving both sorptive uptake by the soil and degradation by hydrolysis in the presence of the soil matrix. The labile sorption capacities for pirimiphos-methyl in the Rhodic and Aquic soils were found to be 0.75 and 0.90 micromol g(-)(1), respectively.

Lead in a Nigerian savanna soil under long-term cultivation.

Concern about heavy metal accumulation in agricultural soils under long-term application of phosphate fertilizers and organic wastes makes investigation of heavy metals in agricultural soils imperative. This study examines the total, available and chemical forms of lead (Pb) in a savanna soil after 50 years of continuous cultivation and application of NPK fertilizers and farmyard manure (FYM). Total Pb concentration ranged from 28 to 42 mg kg(-1) over 2-3 times more than the average Pb concentration of non-polluted soils worldwide. Available Pb was, however, less than 2 mg kg(-1) indicating that Pb in the soils was largely insoluble. There were no detectable concentrations of water soluble and organically-bound Pb fractions. On average, residual Pb accounted for over 80% of total Pb. Compared to the natural site, cultivation and fertilization with NPK and FYM increased total Pb concentration by 19 and 17%, respectively, or, on mass basis, by 10 and 35 kg ha(-1), respectively, after 50 years. Soil Pb showed strong linear relations with sand fraction and inorganic phosphorus in the soils. Thermodynamic equilibrium relations provided some indirect evidence that the control on soluble Pb appeared to be chloropyromorphite [Pb5(PO4)3Cl], an insoluble lead phosphate mineral.

Three new species of Chaetomium from soil

Chaetomium macrostiolatum sp. nov., Chaetomium olivicolor sp. nov. and Chaetomium tarraconensis sp. nov. isolated from Nigerian, Indian, and Spanish soils respectively, are described and illustrated. The first species is characterized by ascomata with a very broad ostiole and yellow hairs, and limoniform ascospores; the second by its thermotolerant growth, inconspicuous and short straight ascomatal hairs and fusiform ascospores; and the last by its unusual, irregularly-shaped ascospores and subglobose ascomata with flexuous to undulate, unbranched ascomatal hairs.

Potassium recovery from farm wastes for crop growth

Potassium (K) is a scarce agricultural chemical, which is being depleted from Nigerian soils at a fast rate. There are no known resources in Nigeria and farmers depend on imported muriate of potash (KCl) for their needs. A study has been undertaken on the potential for resource utilization of potash from known farm wastes available in plentiful supply. Thirteen farm wastes were assessed for their K and other mineral contents. Among them, cocoa waste, plantain waste, market waste, and water hyacinth were found to be rich in their K contents. Varying levels (0, 10, 15, 20, 25, and 30 tons/ha) of these wastes in ash form along with recommended NPK fertilizer were examined in greenhouse experiments using Amaranthus cruentus L. as a test crop. The results indicated that water hyacinth and cocoa waste promoted maximum crop growth and yield when applied at 10 tons ha−1, respectively. Crop growth and yield were significant at the 0.05% level as compared to application of conventional NPK fertilizer at K levels 10 and 20 kg ha−1. From the soil residual K levels and plant uptake, it was observed that the K from water hyacinth seems to be more available to the plant as compared to sources from other farm wastes. Samples of potassium salt in the carbonate form were recovered and concentrated from ash of water hyacinth and cocoa waste which may prove to be economical for farmers in the country to meet K demand of their soils.

Distribution and movement of sludge-derived trace metals in selected Nigerian soils.

Use of metal-rich sewage sludge as soil fertilizer may result in trace- metal contamination of soils. This study was conducted to evaluate the effects of long-term sludge application on trace-metal (Zn, Cu, Pb, and Ni) distribution and potential bioavailability in Nigerian soils under a tropical wet-dry climate. Total metal analyses, sequential chemical fractionation, and DTPA extractions were carried out on samples of control and sludge-amended pedons in Nigeria (a Rhodic Kandiustult and two Rhodic Kandiustalfs from Nigeria, respectively). The sewage sludge applied to the soils contained higher levels of Zn and Cu than Pb and Ni. The control pedon contained low levels of all four metals. Soil enrichment factors (EF) were calculated for each metal in the sludge-amended pedons. Compared with the control soil, the sludge-amended pedons showed elevated levels of Zn and Cu, reflecting the trace-metal composition of the sewage sludge. Zinc and Cu in the sludge-amended soils were strongly enriched at all depths in the profile, indicating that they had moved below the zone of sludge application. The sequential extraction and DTPA analyses indicated that the sludge-amended soils contained more readily extractable and bioavailable metal ions than the unamended soil.

Forms and profile distribution of potassium in typical soils of the lower Benue Valley of Nigeria

Six profiles, derived from Precambrian Basement Complex rocks (mainly gneiss), Cretaceous sediments (mainly shale and sandstone), and Quaternary alluvium, and which are typical of the major agricultural soils in the Lower Benue Valley (Nigeria) were studied with the objective to determine their overall potassium (K) reserves and any relationship between these and other soil properties including their parent materials. Total K in the soils varies from 0.13–27.1 g kg‐1 with average 6.64 g kg‐1. This correlates positively with the clay, and negatively with the sand contents of the soils and is also influenced by their parent materials. The order of abundance according to parent material is: alluvium‐ > Basement Complex (gneiss)‐ ≈ shale‐ > sandstone‐derived soils. The concentrations of readily available K (RAK) in the soils are quite low, accounting for only between 0.30 and 7.8% of the total K in the soils and less than 4.0% of their exchange capacities. Based on critical limits established for many Nigerian soils, the soils derived from sandstone are clearly deficient in RAK, while soils developed from gneiss, shale and alluvium parent materials have moderate to sufficient levels for a wide range of crops. Non‐exchangeable or moderately available K (MAK) in the soils is also relatively low (0.020–8.59 mmolc kg‐1); while the sandstone‐derived soils have the least MAK, the alluvial soils have the most levels. However, the potassium supplying power (KSP) of the soils may be considered to be generally high. Although this bears no particular relationship to soil parent materials, the sandstone‐derived soils have the lowest KSP. The bulk of the total K reserves in the soils (55–88%) exists as difficultly available or structural K (DAK). The alluvial soils first, then the gneiss‐ and shale‐derived soils next have the highest contents of DAK, while the highly weathered sandstone soils have the lowest. Simple correlation analysis shows that, irrespective of parent material and K form, clay content and CEC are the most important soil properties influencing the overall K supplying status of these soils. It is concluded that in major agricultural soils of the Lower Benue Valley of Nigeria K exists mostly in the lattice structures of K‐bearing minerals, with accumulations in the subsurface horizons. Its plant‐available or supplying status is low on sandstone‐derived soils and moderate to sufficient on soils derived from Basement Complex rocks, shales and alluvium.

Nigerian agriculture and the challenges of the 21st century: Nigerian soils

The cardinal roles of agriculture in Nigeria, her landmass, approximate hectares under different land uses, the national average cultivated land ratio per caput, soil studies, government policies on agriculture, soil constraints and problems and technologies of soil conservation and management in the 20th century were reviewed. Their implications on soil and agriculture are discussed. Nigerian soils are found to be of medium to high potentials. There is no class one soil and class two soils account for 5.5% of the total land area. Class three soils constitute 46.5% and they are of medium productivity and have a good potential for agricultural development. Over 48% fall into classes four and five and they generally have low productivity. Soil constraints and problems that militate against high crop yields are soil erosion, salinization, flooding, declining fertility, desert encroachment, mismanagement and misuse etc. Conservation and management measures include adoption of minimum tillage, crop rotation, fallowing, fertilization, mulching etc. The expectations and approaches for the study and use of Nigerian soils in the 21st century are discussed. Some of them include establishment of soil research institutes, detailed characterization and mapping of the soils, production of land capability maps, zoning of crops based on land capability and the suitability of the soils; use of modern methods of acquiring, storing and retrieving data; proper formulation and use of inorganic and organic fertilizers etc. New technologies must be sought to handle the cultivation of the fragile soils. Irrigated agriculture and water conservation techniques should be encouraged at small to medium scale farming. Soils study should be approached from a multi-disciplinary viewpoint for sustained productivity and environmental harmony.

Quantity‐intensity parameters of potassium in relation to uptake by guinea‐corn in representative soils of the ecological zones of Nigeria

Quantity‐intensity (Q‐I) relation studies were often used to supplement information obtained from conventional soil tests for the estimation of potassium (K) needs of crops. With a view to ascertaining the reliability of the Q‐I relation parameters for comprehensive characterization of K dynamics in typical Nigerian soils, K values derived from Q‐I isotherms were related to neutral normal ammonium acetate (1 N NH4OAc, pH 7.0) (exchangeable) K, other soil K forms [non‐exchangeable (Kne), exchange (Ke), mineral K (K m ), and solution K (Ks)] and the K uptake by Guinea‐corn (Sorghum bicolor, var. LS 187) subjected to weekly cuts in Neubauer cultivation vessels. Most of the soil K (about 98%) was in the form of soil minerals while less than 1% was plant available whereas about 1% was trapped within the interlattice layers of the clay minerals (as fixed K or Kne). Mineral K (Km) content was closely related to total K (Kt), but not to the other forms, Kne, Ke, and Ks. A close relationship was noted between the two components of labile K (Ke and Ks). Except for % K saturation, the relationships between the K measurements with plant response were poor. The results of these investigations clearly demonstrate that the Q‐I relation could not adequately characterize the K dynamics of these tropical soils.

Relationship of percolation stability of soil aggregates to land use, selected properties, structural indices and simulated rainfall erosion

Simple tests of structural stability are needed for evaluating the ease with which soils slake and erode when in contact with water. In a laboratory study, we related the percolation stability (PS) of 22 Nigerian soils to land use, soil properties, structural stability indices and simulated rainfall erosion. All measurements were carried out with the 1–2 mm diameter air-dry aggregates. Land use influenced PS more than the type of soil. Forest soils, bush fallows, mulched, minimally tilled plots and pasture lands had rapid PS (>250 ml/10 min) values, whereas mulched conventionally tilled plots, bare fallows and continuously cultivated plots from where residues were removed by burning had relatively slow to moderate PS values (34–241 ml/10 min). The single most important soil property that correlated positively with PS is organic matter (OM) ( r = 0.55 *) followed by total Fe + Al ( r = 0.52 *). The significant inverse relationship ( r = −0.49 *) between log (PS) and log (pH/OM) indicates a decrease in PS of these acidic, low-OM soils with increasing pH levels. The percent water-stable aggregate (WSA) >0.20 mm diameter, aggregated clay index (AC) and clay dispersion ratio (CDR) correlated weakly with PS. Conversely, the sealing index (SI) (i.e. the ratio of saturated hydraulic conductivity of an uncrusted to that of a crusted soil) had a strong, inverse relationship with PS ( r = −0.97 ***). These relationships indicate that PS measures the slakability (and not dispersibility) of soils. The relationship between PS and erosion ( E) was an exponential decay form, E = 102 e −0.0043PS ( r 2 = 0.98) and showed that high interrill erosion rates would be expected on soils with PS < 250 ml/10 min. The PS which is simple to measure, is, therefore, a good indicator of structural stability for assessing the potential of these soils to erode.

Aggregation and organic matter fractions of three Nigerian soils as affected by soil disturbance and incorporation of plant material

Soil management involving organic matter incorporation and reduced tillage intensity has often been reported to improve soil structure. However, the mechanisms and roles of soil organic matter (SOM) fractions in the process of soil structural stabilisation are not well documented. Furthermore, documentation of their positive effects on soils in the tropics is scarce. This study examined the changes in soil structure in response to SOM fractions dynamics in an incubation experiment. Three Nigerian soils: Iwo series (Oxic Tropudalf), Itagunmodi series (Tropeptic Euthrothox) and Owode series (Oxisol) were incubated with ground barley straw ( Hordeum vulgare L.) or green ryegrass ( Lolium perenne L.) with and without disturbance of the soil during incubation. The incorporation of plant material significantly increased the light fraction organic matter (LFOM) with density <1.7 g cm −3 but had no effects on the heavy fraction polysaccharides (HFPS), i.e. polysaccharides attached to heavy fraction soil minerals with density >1.7 g cm −3. A significant decline of LFOM was recorded with time of incubation (0–41 days: 21%, 30% and 36% decrease for the no plant material treatment, the barley straw treatment, and the green ryegrass treatment, respectively). This was associated with a significant rise of HFPS. Furthermore, the added plant material clearly decreased the soils' fraction of dispersible clay even before incubation, which was interpreted as a direct effect of the LFOM on the clay. Therefore, the use of dispersible clay as an indicator of macro-aggregate stability is questioned. After 41 days of incubation the concentration of water-stable aggregates was on an average 9% higher for soils with added plant material relative to soils not receiving plant material. When packing the post-incubation soil in metal cores, the volume of pores with equivalent neck diameter >10 μm was from 0.024 to 0.033 m 3 m −3 higher and the saturated hydraulic conductivity 18–24% higher for soils with added plant material than for soils without. Disturbance of the soil during incubation reduced the concentration of water-stable aggregates by 7% relative to undisturbed. Also the volume of pores with a neck diameter >10 μm and the saturated hydraulic conductivity were significantly reduced (by 6% and 19% relative, respectively) when the soil was disturbed during incubation. The results demonstrate that rapid changes of SOM fractions can occur over a short incubation period and that these changes have a pronounced positive effect on the structure of these tropical soils. It also suggests that incorporated plant material may correct tillage induced degradation of soil physical properties over a relatively short time.

Degradation of 14C-Dichloro-Dipheny1 Trichloro-ethane (DDT) in Nigerian Soils.

Degradation of 14C-Dichloro-Dipheny1 Trichloro-ethane (DDT) in Nigerian Soils.

A PRELIMINARY CHLORINE SURVEY OF THE SAVANNA SOILS OF NIGERIA

Chlorine contents of 32 surface soils representing the four savanna zones in Nigeria, the major soil parent materials and the main agricultural fields were examined. Total chlorine contents varied from 47.2 to 296.5 mg kg-1 while the water-soluble chloride varied from 0.1 to 7.7 mg kg-1 in all the soils. Total Cl and water-soluble Cl- did not vary by either ecological zones or by soil parent material. However, according to the order of magnitude, the contents in the ecological zones may be arranged as follows: Southern Guinea > Sudan > Northern Guinea > Sahel while, with respect to parent material, the contents could be arranged as follows: Basement Complex > Basalt > Sedimentary > Aeolian. Preliminary results tend to indicate that over eighty percent of the Nigerian savanna soils may be deficient in Cl, though detailed study may be necessary. Lack of significant correlation between Cl and selected soil properties tends to indicate that neither texture, organic matter nor soil reaction has a controlling influence on Cl occurrence in the study area.

Evaluation of organic carbon oxidation efficiencies of a modified wet combustion and Walkley‐black procedures in Nigerian soils

The organic carbon (C) oxidation efficiencies of the Walkley‐Black and modified wet combustion procedures were evaluated in soil samples taken from different ecological zones and diverse parent materials in Nigeria. Dry combustion using a C analyzer was the standard to evaluate the efficiency of the modified wet combustion method. The efficiency of the Walkley‐Black method was later compared to that of the modified wet combustion procedure. The results indicated that the modified wet combustion and the dry combustion procedures were highly correlated (r=0.99**)‐Significant correlation (r=0.96**) was also found between the Walkley‐Black and the modified wet combustion procedures. There was no correlation between the C data obtained using the modified wet digestion method and the % DCB‐Fe2O3. These results suggest the absence of strong organo‐mineral complexes in these soils. Organic C recoveries by the Walkley‐black method were not affected by fine‐grinding (<0.5 mm) of the soil samples. It is suggested that both the modified wet combustion and the Walkley‐Black methods may be used without a correction factor in Nigerian soils. The modified wet combustion procedure was also found to be an adequate substitute for the dry combustion procedure.

Evaluation of phosphorus availability from three phosphorus sources in Nigerian soils

In an attempt to search for a cheaper source of phosphorus (P), both for direct application and industrial use, three P fertilizers were evaluated in incubation and greenhouse studies. Indigenous Sokoto rock phosphate (SRP) imported, Togo rock phosphate (TRP), and conventional single superphosphate (SSP) were applied on three soil types namely Oxisol, Ultisol, and Alfisol at rates ranging from 0–800 mg P kg‐1 soil. Evaluation of the P sources was conducted for 12 weeks in incubation study, and five weeks in the greenhouse using maize as test crop. Evaluation of direct application of SSP and SRP on an oxic paleudult was carried out in the field for three years. The results of incubation studies revealed in general, that P availability increased as fertilizer rates increased. The P availability was, however, greater when SSP was applied on the Alfisol than on the Oxisol and Ultisol. The rock phosphates on the other hand were more efficient on acid soils than on soils neutral in pH. Optimum P availability from the fertilizers was observed to occur predominantly between four and eight weeks of incubation. In the greenhouse study, SSP gave the highest cumulative P uptake and optimum rate of application was 200 mg P kg‐1 soil, while optimum rate for rock phosphate was 400 mg P kg‐1 soil. The agronomic effectiveness (EA) of the rock phosphates was about 40% relative to SSP on the Alfisol. The EA, however, for TRP and SRP was 120% and 160%, respectively, on the Oxisol, while on the Ultisol, SRP was equally effective as SSP and TRP had 65% effectiveness. The results of the field trial indicated that the SRP had 54%, 83%, and 107% agronomic effectiveness of SSP, respectively, in the first, second, and third year of cropping. Optimum rate for SSP and SRP application was considered to be 50 and 75 kg P2O5 ha‐1, respectively.

A study of soil factors in relation to erosion and yield of maize on a Nigerian soil

The study aimed at quantifying the effects of erosion on the productivity of a Nigerian soil involved the use of a half hectare farmland with history of various degrees of erosion severity. The farmland was divided into 3 different classes; class I (uneroded), class II (slightly eroded) and class III (moderately eroded) based on the degree of erosion severity and were then planted with maize. The mean topsoil's (0–15 cm) colour hue reduced from 7.5YR on class I to 5YR on class III soils (representing colour change from dark brown to dark reddish brown) on Munsell's colour chart. The soil properties and the maize yield on the farmland exhibited strong spatial variability, the trend of which appears to have been influenced by the topography of the area. The mean yield on the class II plots and the class III plots were 80% and 65% respectively of that in class I plots. Because of the strong functional dependencies identified among many of the variables, multivariate statistical procedure was used to identify the variables that influence maize yield. Seven components were selected based on factor analysis. These components when regressed against maize yield, were found to explain 95% of the variability in maize yield. The yield of maize on this soil was found to be determined by soil properties such as; bulk density, organic carbon, topsoil thickness, texture, pH and gravel content in the topsoil, and by base saturation, organic carbon and exchangeable acidity in the subsoil.

Mosquitocidal Bacillus thuringiensis from Nigerian soils

Out of 85 Bacillus thuringiensis strains isolated from Nigerian soils, 18 were larvicidal to Aedes aegypti, Culex quinquefasciatus and Anopheles gambiae . At 10 −6 dilution of the final whole culture (FWC), the 11 most active strains, code-named GSC1, GSC3, GNA13, GNA14, OGL8, BUS4, BUS5, OBG1, OBG4, OBG8 and BAR3 produced mortality of 11.7–61.7% and 3.3–48.3% in Ae. aegypti and in C. quinquefasciatus fourth instars respectively. At 0.5 × 10 −5 dilution of the FWC, the B.t . strains caused mortality in An. gambiae larvae ranging from 31.7 to 94.1%. All the 18 mosquitocidal isolates belonged to the subspecies israelensis , i.e. serotype 14. Microscopic examination revealed all the isolates to be typically Bacillus , with irregular or amorphous crystals of varying sizes.

Selected physico‐chemical characteristics of soils from the sub‐humid and semi‐arid zones of Nigeria

Soil samples obtained from basement complex soils which spread across the major soil areas in northern Nigeria were analyzed for both physical and chemical properties. The soils are slightly acid. Acidity decreased with depth. The textural class ranged from sand in the semi‐arid areas to sandy clay loam in the southern part of the sub‐humid zone. Organic carbon content ranged from 0.17 to 1.5%, whereas nitrogen (N) levels ranged from 0.04 to 0.08% in the surface horizon. The soils have high base saturation indicating low Al3+concentration. The levels of available phosphorus (P) were inadequate for satisfactory plant growth, given a critical level of 15 mg kg‐1 was established for Nigerian soils. A significant correlation (r=0.63) was observed between pH and P on one hand and with clay content (r=0.47) on the other hand. The low values of the silt:silt + clay ratio, used as a weathering index indicated that the soils must have undergone advanced weathering. The magnitude of calcium:magnesium (Ca:Mg) ratio indicated that more calcium than magnesium was available in the soils. More iron than aluminum was extracted from soils by the dithionite‐citrate method. Soils from the sub‐humid zone had relatively higher levels of organic matter and total N than the semi‐arid areas. In the same vein, marginal higher values for sand and base saturation were found in soils from the semi‐arid areas than the sub‐humid zone.

Estimating water retention and availability in Nigerian soils from their saturation percentage

A possibility of estimating the field capacity (FC), wilting point (WP), total available water (TAW), and readily available water (RAW) of soils was investigated from their saturation percentage (SP). Regression equations were obtained from the data from 166 Nigerian soils with wide variations in texture and other physico‐chemical properties. The results showed a strong linear relationship between saturation percentage and the gravimetric percentage moisture contents at FC (r=0.972, P<0.001), and WP (r=0.949, P<0.001), but a weak linear relationship with TAW (r=0.771, P<0.01) and RAW (r=0.489, P<0.05). The regression equations calculated between these soil moisture constants and SP predicted the FC and WP of 25 independent soils very well, but were not good predictors of TAW and RAW. Reliable and satisfactory estimates of TAW were obtained by subtracting estimated WP from estimated FC, and of RAW by subtracting estimated moisture content at ‐100 kPa matrix potential from estimated FC.

Long-term tillage and maize monoculture effects on a tropical Alfisol in western Nigeria. II. Soil chemical properties

Intensive monocropping of maize is widely practised in densely populated regions of west Africa. A wide range of tillage systems are used for seedbed preparation without the benefits of research information from long-term experiments relating tillage method to soil properties. Soil chemical effects of eight tillage and residue management treatments were studied for 8 years or 16 consecutive maize monoculture crops for a western Nigerian soil with a coarse-textured surface horizon. Treatments established on a newly cleared land were: (1) notill ± crop residue mulch, (2) notill ± chiselling in the row zone at 50 cm depth, (3) mouldboard ploughing ± harrowing, (4) disc ploughing ± rotovation, (5) notill − residue mulch, (6) mouldboard ploughing at the end of rains or summer ploughing, (7) mouldboard ploughing ± residue mulch, and (8) mouldboard ploughing and harrowing ± ridging or ridge till. Soil chemical properties of the 0–5-cm and 5–10-cm depths were measured during the dry season every year beginning with base line characterization soon after land clearing in 1980. Soil pH declined with cultivation duration from 6.6 in 1981 to 5.4 in 1987 for the 0–5-cm depth, and from 6.5 in 1981 to 5.5 in 1987 for the 5–10-cm depth. Mean soil pH for the 0–5-cm depth declined from 6.7 to 5.6 in notill ± residue mulch, and from 6.7 to 5.4 with mouldboard ploughing. Soil content of Bray P increased with cultivation duration due to application of phosphatic fertilizers. There occurred a significant decrease in soil organic carbon (SOC) and total soil nitrogen (TSN), and an increase in C:N ratio with cultivation duration. Mean SOC content in 1987 of the 0–5-cm depth was 13.9 g kg −1 for the notill treatment compared with 11.0 g kg −1 for the plough-based methods. Soil concentration of Ca and Mg and total cation exchange capacity (CEC) increased with cultivation duration. Maize grain yield was significantly correlated with SOC, exchangeable Ca 2+, and CEC. Continuous cropping decreased soil chemical quality, and the rate of decreases was more with plough-based than notill methods.

Growth, Nodulation and Yield of Bambara Groundnut (Vigna subterranea (L) Verdc) on Selected Nigerian Soils

To compare their performances in terms of growth, nodulation and yield, six bambara groundnut lines collected from Benue, Bauchi, Enugu and Sokoto states of Nigeria were grown on five different Nigerian soils: alfisol, entisol, inceptisol, ultisol and vertisol. Data obtained showed that the soil reaction did not impair the nodulating capacity of the genotypes except at very low pH values. Best performances in terms of growth and yield were observed in vertisol. Nodulation, growth and yield were consistently depressed in entisol and inceptisol. The ease of penetration of the different soils measured at field capacity, during pegging, was an important factor in the cultivation of bambara groundnut. There were strong evidences of differential pod and seed yields per plant by the genotypes on the different soils. © 1997 SCI.