S. O. Adesiyan's research while affiliated with University of Ibadan and other places

Cogongrass is an aggressive perennial weed, which causes severe yield losses in major crops of the moist savanna of West Africa. Field studies were conducted from 2000 to 2002 at Alabata and Ilorin, Nigeria, to evaluate the influence of dosage and time of nicosulfuron application on the control of cogongrass and corn grain yield. Nicosulfuron dosages were 50, 100, 150, and 200 g ai/ha applied 1, 2, 3, or 4 wk after planting (WAP) corn. Hand-weeded and nonweeded treatments were the controls. Three to 4 wk after treatment and at final harvest, all plots that received nicosulfuron had significantly lower cogongrass shoot dry matter (DM) than the nonweeded control across locations in all years (P ≤ 0.01). Nicosulfuron increased corn grain yield at Alabata by 96% in 2000, 100% in 2001, and 34 to 54% in 2002, and at Ilorin by 79 to 83% in 2001 and 60 to 69% in 2002 when compared with the nonweeded control. The weeded control had corn grain yield similar to plots that received nicosulfuron at 200 g/ha at Alabata in 2001, 150 g/ha at Ilorin in 2001, 50 to 200 g/ha at Alabata in 2002, and 150 and 200 g/ha at Ilorin in 2002. There were negative linear relationships between corn DM, grain yield, and cogongrass shoot DM. Application of nicosulfuron at 1 or 2 WAP, when cogongrass was 22 to 27 cm tall, gave better grain yield and lower cogongrass shoot DM than at 3 or 4 WAP, when cogongrass was 36 to 45 cm tall. The study concludes that 150 to 200 g/ha of nicosulfuron applied at 1 or 2 WAP is effective for cogongrass control without adverse effect on corn grain yield. Nomenclature: Nicosulfuron; cogongrass, Imperata cylindrica (L.) Beauv. #3 IMPCY; corn, Zea mays L. Additional index words: Crop injury, sulfonylurea herbicide, weed competition. Abbreviations: DM, dry matter; WAP, weeks after planting; WAT, weeks after treatment.

Studies on the effect of gamma irradiation on yam tubers infected with Scutellonema bradys showed that dosages between 5 and 15 krad did not eliminate the nematodes completely, but suppressed sprouting and signs of deterioration in the tubers. Dosages between 20 and 30 krad eliminated 70–80 % of the nematode population in yam peels. The appearance and taste of yams treated with between 7·5 and 15 krad were generally acceptable to a panel of tasters.

Control of plant-parasitic nematodes essentially involves use of synthetic nematicides. However, apart from cost, increased concern for the environment has necessitated a reduction in the amount of nematicides used for control. Additionally, there has been an increase in the search for other efficient; ecologically sound and safe control methods. Eggs of root-knot nematode, Meloidogyne incognita (Kofoid & White) Chitwood, were exposed to concentrations of root extracts of Siam weed [Chromolaena odorata (L.) King and Robinson], Neem (Azadirachta indica A. Jass), Castor bean (Ricinus communis L.) and Lemon grass (Cymbopogon citratus L.). Undiluted (100%) concentrations of root extracts of Siam weed and Neem exhibited 100% inhibition of egg hatch and larval mortality, while the 100% concentration of root extracts of Castor bean and Lemon grass exhibited 93 and 95% inhibition of egg hatch and 62 and 75% larval mortality, respectively. Egg hatch inhibition and larval mortality decreased as extracts were diluted. With an increase in exposure time, juvenile mortality increased for the diluted concentrations, but time had no effect on juvenile mortality at the 100% concentration for all of the plant species.

An oil spill polluted site at Ogbodo-Isiokpo in Ikwere Local Government Area of Rivers State in southern Nigeria, was identified for study following three successive reconnaissance surveys of oil fields in the Agbada west plain of Eastern Niger Delta. A sampling area of 200 m x 200 m was delimited at the oil spill impacted site using the grid technique and soils were collected at surface (0-15 cm) and subsurface (15-30 cm) depths from three replicate quadrats. A geographically similar, unaffected area, located 50 m adjacent to the polluted site, was chosen as a control (reference) site. Total extractable hydrocarbon contents of the polluted soils ranged from 3.02-4.54 and 1.60-4.20 mg/kg (no overlap in standard errors) at surface and subsurface depths respectively. The concentrations of two "diagnostic" trace heavy metals, nickel (Ni) and vanadium (V), which are normal constituents of crude oil, were also determined in the soils by atomic absorption spectrophotometric method after pre-extraction of cations with dithionite-citrate carbonate. Ni varied from 0.15 to 1.65 mg/kg in the polluted plots and from 0.18 to 0.82 mg/kg in the unpolluted plots; vanadium varied from 0.19 to 0.70 mg/kg in the polluted plots and from 0.14 to 0.38 mg/kg in the unpolluted plots. Ni and V were more enhanced (p < 0.05) in the oil-polluted soils, especially at subsurface depth. Whilst the oil spillage could be said to be indirectly responsible for the enhanced concentrations of nickel and vanadium via the injection and availability of the petroleum hydrocarbons that might have increased the activities of biodegradation on site, the physico-chemical properties of the soils and inherent mobility of metals, as well as the intense rainfall and flooding that characterized the period of study, may have also contributed, at least in part, to these enhanced concentrations. Such levels of Ni and V may result to enhanced absorption by plants, which may bring about possible bioaccumulation in such plants and the animals that depend on them for survival and all of these may lead to toxic reactions along the food chain.

The environmental impact of the 1997 leakage of the high-pressure crude-oil pipeline at Isiokpo in the Niger Delta in the southeast of Nigeria was evaluated, with particular reference to total-organic-carbon (TOC) and total-organic-matter (TOM) contents of soils within the vicinity of the oil spillage. The soils, taken from depths of 0-15 cm (surface) and 15-30 cm (subsurface), were found to be more acidic (pH 4.2-5.6) than the unpolluted soils, with a high average moisture content of 6.8%. The extractable hydrocarbon content ranged from 2.71-3.48 mg/kg, indicating hydrocarbon contamination. However, contrary to expectation, the TOC and TOM contents of the polluted soils did not show any significant increase in concentration, supposedly due to natural rehabilitation of the affected mat layer of soils. Thus, notwithstanding the possible proliferation of heterotrophic organisms by the presence of the added petroleum hydrocarbons, environmental conditions such as weathering and climatic predispositions, as well as physico-chemical parameters such as pH, moisture content, and temperature must have encumbered the carbon-mineralizing capacity of the heterotrophs, thereby reducing the turnover of carbon and the decomposition of organic matter. The restrictions by high moisture content might not come directly from H(2)O itself, but are probably a consequence of hindered soil ventilation, which reduces O(2) supply and gaseous diffusion, conditions that might have been substantially aggravated by the added petroleum hydrocarbons.

Imperata cylindrica (speargrass) is one of the most invasive weeds in the moist savannah zone of sub-saharan Africa. This study was conducted in 2001 and 2002 at Ijaye and Ilorin, Nigeria, to investigate the influence of four nicosulfuron doses (35, 70, 105, and 210ga.i./ha) on the performance of maize, and its efficacy in the control of Imperata. The experiment was designed as a split-plot with three replications. Nicosulfuron was applied 2 weeks after planting maize. Hoe weeded and unweeded treatments were controls. In both years, 7 weeks after treatment, the unweeded control had lower maize leaf area index (LAI) (19% at Ijaye and 25% at Ilorin) than the weeded control. Maize LAI was highest in plots that received 35ga.i./ha of nicosulfuron at Ijaye and the weeded control at Ilorin in both years. All plots that received nicosulfuron had significantly higher maize grain yield than the unweeded control at both locations in both years. Maize grain yield in the weeded control was similar to plots that received nicosulfuron at 35–210ga.i./ha at Ijaye in 2002, 70–210ga.i./ha at Ilorin in 2001, and 35ga.i./ha at Ilorin in 2002. The protein content of maize in the weeded control and at 70ga.i./ha was similar and higher than that at doses of 105 and 210g a.i./ha (P⩽0.01) while the carbohydrate content was not significantly different. The unweeded control had significantly higher weed LAI, shoot and rhizome biomass than all other treatments at both locations in both years (P0.05). An increase in the nicosulfuron dose led to a decrease in weed LAI. Imperata rhizome biomass in the weeded control was similar to that in all nicosulfuron-treated plots. The findings of this study show that nicosulfuron is a suitable postemergence herbicide for speargrass control in maize in the moist savannah of Nigeria.

Twelve crops commonly grown in association with yam in South-Western Nigeria were evaluated for resistance to root-knot nematode Meloidogyne incognita (Kofoid and White 1919) Chitwood 1949, race 2 infection using the quantitative modification by Sasser et al. (1984) of host suitability designations of Canto-Saenz (1983) for plants infected with root-knot nematode in 1998 and 1999 planting seasons. Observations, based on gall indices and recovery of the juvenile larvae from the roots and soil indicated that Abelmoschus esculentus, Corchorus olitoris cv Angbadu and Sphenostylis stenocarpa cv Nsukka Brown were highly susceptible, while Arachis hypogaea cv UGA 4, Cajanus cajan cv Cita-2, Cucumis melo cv Bara To139, Manihot esculenta cv TMS 30572, Sorghum bicolor and Zea mays cv DMR-LSR-Y were hyper-susceptible to Meloidogyne incognita race 2 with reproductive factor and gall index of ≤1 and ≥2 respectively. Crotalaria juncea, Mucuna cochinchinensis and Stylosanthes gracilis were resistant to Meloidogyne incognita race 2 with reproductive factor and gall index of ≤1, ≤2 and ≥2 respectively. These intercrops if planted on yam mounds will play a prominent role in altering the populations of root-knot nematode Meloidogyne incognita race 2.

Chemical control of plant-parasitic nematodes, essentially, involves the use of synthetic nematicides. However, apart from its very high cost, increased concern for the environment has necessitated a reduction in the amount of nematicide used for nematode control. Additionally, there has been an increase in the intensity of search for other efficient, ecologically sound and safe control methods. Meloidogyne incognita (Kofoid and White) Chitwood, eggs were exposed to concentrations of root extracts of Siam weed [Chromolaena odorata (L.) King and Robinson], Neem (Azadirachta indica A. Jass), Castor bean (Ricinus communis L.) and Lemon grass (Cymbopogon citratrus (DC.) Stapf). One hundred percent concentration of root extracts of Siam weed and Neem exhibited 100% inhibition of egg hatch and larval mortality. While 100% concentration of root extracts of Castor bean and Lemon grass exhibited 93 and 95% inhibition of egg hatch and 62.1 and 75% larval mortality respectively. Egg inhibition and larval mortality decreased with an increase in the dilution of all the extracts. Similarly with an increase in exposure time, juvenile mortality was also increased. Significant differences were also observed in the concentrations of the root extracts in respect of the two parameters.

Nicosulfuron is a new alternative herbicide for post-emergence control of perennial weeds in maize. Field studies were conducted to evaluate the response of four maize cultivars (Low-N-Pool, TZB-SR, Oba Super-1 and Oba Super-2) and speargrass to different rates of nicosulfuron (35, 70, and 105 g a.i. ha − 1). Hand-weeded and unweeded plots were controls. All plots that received nicosulfuron had significantly lower speargrass shoot biomass than the unweeded control 3 weeks after treatment and at crop harvest. Maize biomass was highest in the weeded control in both years. In 2000, maize biomass in plots that received 35 g a.i. ha − 1 of nicosulfuron was similar to that in the unweeded control, and in both cases was higher than in all the other nicosulfuron treatments. In 2001, all rates of nicosulfuron produced significantly higher maize biomass than the unweeded control. Higher maize grain yield was obtained from 70 and 105 g a.i. ha − 1 than from 35 g a.i. ha − 1. All the cultivars responded similarly to nicosulfuron. A linear regression equation is given for grain yield and speargrass biomass. Our results suggest that nicosulfuron has the potential for effective speargrass control in Nigeria.

Typical post-impact assessment of an oil-spill-impacted site in Agbada west plain of the Niger Delta basin of Nigeria was carried out 13 months after recorded incidence of spillage, using empirical indices of reconnaissance and extractable hydrocarbon content. Field-reconnaissance surveys revealed lower species' numbers and diversity of surface and subterranean flora and fauna. The presence and absence of such plant species as Elaeis guineensis, Musanga cecropiodes, and Andropogon gayanus, as well as animal species like earthworms and nematodes in sampled plots, corroborated the evidence provided by the total extractable hydrocarbon content (of (2.53+/-0.43)x10(2) mg/kg and (2.00+/-0.76)x10(2) mg/kg at surface and subsurface depths, resp.) on the level of degradation and/or regeneration at the polluted site. The most important evidence that oiling must have been responsible, at least in part, for the reduction in species' number and diversity was provided by the plant cover, Andropogan gayanus, which occurred at a lower density of 0.9 plants/m2 in the oil-impacted plots and 14.00 plants/m2 in the unimpacted reference plots of an adjacent, geographically similar area. The presence of this species on site thus presented a significant difference (P<0.05) of over 85%, and indicated exhaustion or impoverishment of impacted soils. Elaeis guineensis, with a population density of 0.1 stands/m2, provided evidence of past cultivation on site, while species like Musanga cecropioides, with a density of 0.5 stands/m2, at the unimpacted site, confirmed the abandonment of the farmstead over a long period of time. For the fauna, the most sensitive indicator of hydrocarbon toxicity was provided by nematode Xiphinema sp. that were completely absent in the oil-impacted site.