Effect of chloroxuron on some microbial activities in soil

The effect of chloroxuron on some soil microbial activities, i.e. carbon dioxide evolution, mineralisation of nitrogen, dehydrogenase activity and on microbial colony counts, was assessed by applying different concentrations of the herbicide to soils incubated under laboratory and glasshouse conditions. Experimental results showed no adverse effects on microbial activities in the soils studied when chloroxuron was applied in concentrations up to 100 ppm. Mineralisation of nitrogen and carbon dioxide production were slightly enhanced by the herbicide.     

Multiple virus infections of lablab [<Emphasis Type="Italic">Lablab purpureus</Emphasis> (L.) Sweet] in Nigeria

Leaf samples of Lablab purpureus collected from two agroecological zones of Nigeria—the northern guinea savanna zone (NGSZ) and the derived savanna zone (DSZ)—were infected with viruses when serologically indexed against available antisera. Approximately 31.1 and 81.1% of the leaf samples collected from the NGSZ and DSZ, respectively, were infected. Seven viruses were found: Bean common mosaic virus (BCMV), Cowpea aphid-borne mosaic virus (CABMV), Cucumber mosaic virus (CMV), Cowpea mottle virus (CPMoV), Cowpea severe mosaic virus (CPSMV), Southern bean mosaic virus (SBMV) and Tobacco mosaic virus (TMV) were detected from samples collected from NGSZ, while CMV, CPMoV, Cowpea mosaic virus (CPMV) and CPSMV were detected from samples from DSZ.     

Responses of white yam (Dioscorea rotundata) cultivars to inoculation with three viruses

The responses of 24 white yam ( Dioscorea rotundata ) cultivars to mechanical and vector transmission with each of three viruses infecting yams were assessed through enzyme-linked immunosorbent assay (ELISA) and symptom development. The viruses were Dioscorea alata virus (DAV), genus Potyvirus ; Dioscorea alata bacilliform virus (DaBV), genus Badnavirus ; and Cucumber mosaic virus (CMV), genus Cucumovirus . Only TDr 95-128, a landrace cultivar from Nigeria, developed symptoms of infection with CMV and DaBV following mechanical and vector transmission, respectively. PAS-ELISA showed that nine genotypes remained uninfected by DAV and 11 were uninfected by CMV or DaBV. Genotypes TDr 747 and TDr 1640 both showed resistance to all three viruses.     

Effect of soil application of chloroxuron,metobromuron and fluometuron on nodulation,growth and nitrogen fixation by Centrosema pubescens and Vigna sinensis

The effect of soil applications of three phenylurea herbicides on the growth, nodulation and nitrogen fixation by Centrosema pubescens and Vigna sinensis under two plantings in pots were investigated under glasshouse conditions. Toxicity increased in the order chloroxuron < metobromuron < fluometuron with both legumes. C. pubescens was more susceptible to the effects of the herbicides than V. sinensis. The effects during cropping of C. pubescens and V. sinensis immediately after herbicide application and 9 months later was observed on nodule formation, plant growth and the proportion and quantity of nitrogen in the soil and in dry matter in the plant roots and tops. The levels at which the applied herbicides controlled weeds without any injurious effects on the legumes were for chloroxuron 0.5–2.0 mg/kg and for metobromuron 0.5–1.0 mg/kg but fluometuron killed weeds and was toxic to the legumes at the lowest concentration used (0.25 mg/kg).     

An assessment of non-symbiotic nitrogen fixation in some Nigerian soils by the acetylene reduction technique

Short-term incubation studies of non-symbiotic nitrogen fixation using acetylene as the substrate for nitrogenase were carried out on six soil samples collected from various locations in the Western State of Nigeria, and on one soil sample collected from Wisconsin, U.S.A. Unamended soils reduced a very small amount of acetylene but with added organic materials (5% organic matter, 2% glucose or sucrose) acetylene reduction became substantial and in one case was more than 30,000 times that in the unamended soil. In general, more acetylene was reduced in anaerobic than in aerobic soils. Two of the soils were tested for suppression of acetylene reduction by NH₄⁺-N. With the addition of up to 100 ppm nitrogen as (NH₄)₂SO₄ to the soils incubated with sucrose, no depression of acetylene reduction was observed in one soil while it was reduced by about half in the other.     

Effects of soil,grass and legume root extracts on heterotrophic bacteria,nitrogen mineralization and nitrification in soil

The effects of root extracts of four grasses and two legumes and extracts of soils supporting these plants on the growth of five strains of heterotrophic soil bacteria, and on the rate of nitrogen mineralization and nitrification were measured in culture and in soil. All the root extracts inhibited the growth in culture of the five bacteria by 9–98 per cent. The legume-soil and one of the grass-soil extracts did not inhibit bacterial growth. Only two of the grass-soils, Andropogon lectorum and Pennisetum purpureum markedly inhibited the five bacteria. Incubation of soils with extracts of grass roots or grass-soil increased the rates of nitrogen mineralization and nitrification and incubation with legume root and soil extracts increased the rates of nitrogen mineralization and nitrification even further.