Benjamin D. K. Ahiabor

Maize-grain legume intercropping for enhanced resource use efficiency and crop productivity in the Guinea savanna of northern Ghana

Highlights • Productivity of different intercropping patterns was tested in Guinea savanna of northern Ghana.• Land Equivalent Ratios in intercropping systems are greater under low soil fertility conditions.• Competitive balance between intercrops in poor fields leads to greater Land Equivalent Ratios.• Within-row maize-legume intercropping is more productive than distinct row systems.• Radiation use efficiency is higher in intercrops than in sole crops.

N 2- fixation and N contribution by grain legumes under different soil fertility status and cropping systems in the Guinea savanna of northern Ghana

Highlights • Cropping system and soil fertility effects on N2-fixation were tested in northern Ghana.• More N2 is fixed in sole cropping than intercropping despite comparable %Ndfa.• Poorly fertile fields give limited grain legume benefits despite enhanced %Ndfa.• Partial N balances are unreliable indicators of cropping system sustainability.• Different grain legumes should be targeted to different sites in the Guinea savanna.

COWPEA (VIGNA UNGUICULATA) CROPS IN AFRICA CAN RESPOND TO INOCULATION WITH RHIZOBIUM

Cowpea (Vigna unguiculata L. Walp) is the most important food grain legume in Africa. Cowpea is nodulated by rhizobium bacteria in almost all soils of the tropics, but studies performed in the 1970s and 1980s in Nigeria suggested only modest responses of grain yield in the field to inoculation of selected rhizobium strains. More recently, experiments performed in Brazil have shown that cowpea responded to inoculation of rhizobium selected locally and grain yields increased by up to 30%. We tested some of the Brazilian strains on cowpea at a site in northern Mozambique and at several sites in Northern Ghana. At all sites phosphorus fertilizer (26 kg P ha⁻¹) was added to all plots. At the site in Mozambique despite considerable damage to the crop by the parasitic yellow witchweed (Alectra vogelii), grain yields were more than doubled by inoculation of one of the Brazilian strains and reached 1.4 Mg ha⁻¹. In on-station experiments conducted in 2012 in June and August in northern Ghana using the local cowpea variety Padi-Tuya as the test crop, nodule weight at 35 days after planting (dap) tripled with rhizobium strain BR 3299 (530 mg plant⁻¹) in August with the other inoculants (BR 3267 and a mixture of BR 3267 and BR 3299) also increased nodule weight to over 300 mg plant⁻¹. In the first on-station experiment, grain yields were doubled by the inoculation of any of the three rhizobium strains, and in the second experiment, significant increases in grain yield ranged from 39% to 57% and reached over 2.0 Mg ha⁻¹. Similar increases in nodulation and grain yield due to inoculation were observed in 22 on-farm trials. Nitrogen fertilizer application promoted vegetative growth but did not increase grain yield and nodulation. Inoculating cowpea with highly effective rhizobium strains can therefore enhance grain yield of smallholder farmers in Africa.

PCR assay for direct specific detection of Bradyrhizobium elite strain BR 3262 in root nodule extracts of soil-grown cowpea

AimsSuccessful inoculation of legume crops with rhizobia depends on dominating nodule occupancy with highly efficient strains. The aim of this study was to develop a rapid and reliable conventional PCR methodology to specifically detect an elite Bradyrhizobium strain in root nodule extracts from soil-grown cowpea plants.MethodsThe draft genome sequence of Bradyrhizobium pachyrhizi BR 3262 was compared to the closely related strain PAC 48T. BR 3262-specific regions were selected to design specific primer pairs, which were tested with respect to PCR amplification specificity and efficiency on extracted DNA, bacterial cells and root nodules from cowpea plants grown under gnotobiotic conditions and in soil.ResultsEleven designed primer pairs were specific for BR 3262 amplification and two of them (pairs 2645 and 2736) were highly sensitive and selected for further analyses. Experiments with gnotobiotic and soil-grown plants showed that both primer pairs were suitable to reliably determine nodule occupancy and confirmed the competitiveness of strain BR 3262 in natural soil.ConclusionsPrimer pairs 2645 and 2736 are novel tools to accompany the fate of strain BR 3262 in inoculation experiments of cowpea in soil. This strategy should be applicable to other rhizobium/legume symbioses in the field.

Establishing the link between market orientation and agricultural commercialization: Empirical evidence from Northern Ghana

This paper established a positive relationship between market orientation and intensity of commercialization among rural farm households in northern Ghana. The IV Tobit regression estimate suggests that intensity of maize commercialization is significantly determined by education, agro-ecology, household size, total livestock units, farm size, access to formal markets and market orientation. In addition, a highly and unbiased significant positive effect is observed between market orientation and intensity of maize commercialization after controlling for endogeneity in market orientation. Intensity of maize commercialization increased by 0.86% for a 0.1 unit increase in the market orientation index. The empirical implications of the results are discussed.

Immobilized Laccase Mediator-Catalyzed Oxidation of Aqueous Mixtures of Polycyclic Aromatic Hydrocarbons

ABSTRACT Although terrestrial and aquatic environments are polluted with mixtures of polycyclic aromatic hydrocarbons (PAHs), much of the research efforts toward bioremediation of these toxic, mutagenic and/or carcinogenic pollutants have focused on individual compounds. The potential of laccase (E.C. 1.10.3.2) from Trametes versicolor immobilized on soil and kaolinite for in vitro oxidation of equimolar concentration of anthracene (AnT), benzo[a]pyrene (BaP), benz[a]anthracene (BaA) and pyrene (PyR) in sole, binary, ternary and quaternary substrate systems, in the presence of 2, 2-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and 1-hydroxybenzotriazole (HBT) as mediator compounds was investigated. Results indicated that HBT was a better mediator compared to ABTS due to favorable redox potential difference (ΔEo) between laccase-HBT and PAH couples. The amount of each PAH oxidized depends on the type and number of PAHs present in the mixture. Due to its low molecular weight and high Eo, AnT inhibited the oxidative transformation of the other PAHs, and appeared to be competing for the same active site of the enzyme with BaP. Except for AnT, the oxidation of all the PAHs decreased with complexity of the mixture, with PyR oxidation inhibited by the presence of BaA. The oxidation of the PAHs was significantly low in the quaternary substrate system, probably due to enzyme inhibition from substrate overload. The results indicated that competitive effect may arise when more than one PAH is present in the reaction solution to interact with the enzyme and offer the possibility of the use of immobilized LMS for remediating complex PAH mixtures in the environment.

Bacteria related to Bradyrhizobium yuanmingense from Ghana are effective groundnut micro-symbionts

Highlights • Native rhizobium strains effectively nodulated a popular groundnut variety in Ghana.• Rhizobium inoculation increased biological N2 fixation in groundnut grown in soil.• Ghanaian groundnut strains are genetically related to Bradyrhizobium yuanmingense.• Native isolates are a potential source of strains for local inoculant production.