Soils are polluted by both organic and inorganic substances. Plants growing in polluted soils suffer damages such as leaf rolls, chlorosis, growth inhibition, root tips browning, and death of plant. Soil pollutants such as hydrocarbon and heavy metals are absorbed by crops and such ends up being consumed by human posing health risk like cancer and respiratory abnormally. Conventional methods of remediation such as chemical and physical methods are very expensive and not sustainable. Excavation, which is a type of physical method, merely shifts the pollutant from one site to another. Bioremediation is a biological method of reclaiming polluted soils. Bioremediation is less expensive and more sustainable and safer when compared to the conventional methods of reclamation of polluted environment. This biological method of remediation is an extremely attractive, important, and productive alternative for cleaning, debugging, managing, and rehabilitating and consequently ameliorating contaminated environments via judicious utilization of microbial activities. The rate, at which the waste substances are degraded, is usually dictated by competitiveness among biological agents, sub-optimal supply of essential nutrients, unconducive abiotic conditions (in forms of temperature, aeration, pH, and moisture), and constrained pollutant’s bioavailability. Bioremediation is often effective only under conducive environmental conditions favorable for microbial growth and development. It has been successfully used at various parts of the world. Based on the significance of bioremediation in enhancing the reclamation of polluted environments by decontaminating and degrading heavy metals and xenobiotics, more focused researches would be needed so as to improve contaminated environments in much safer ways and conditions through bioremediation techniques. This research discussed the various types and methods of bioremediation. The mechanisms of actions and strategies of microorganisms in bioremediation were well expatiated. The interaction between bioremediators and the mineral particles in the soil environment was explained.

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Biological nitrogen fixation (BNF), brought about by both free living soil microorganisms and their symbiotic associations with higher plants, is the major source of N input into agricultural systems. Groundnuts (Arachis hypogaea L.), in symbiosis with rhizobia, in their root nodules, fix atmospheric nitrogen (N 2). A field trial was carried out at Samaru, Nigeria, in 2008 with a view to evaluate BNF potentials of five groundnut genotypes (SAMNUT 10, 11, 21, 22 and 23). Each genotype received four rates of P (0, 20, 40 and 60 P 2 O 5 ha-1) in an RCBD with three replications. N-Difference method was employed in assessing the BNF of the genotypes. Nodulation performance of the genotypes was observed. Results of the study showed that SAMNUT 11 and 22 significantly recorded the highest nodulation, by number and weight. All the remaining genotypes statistically produced same nodule number. Moreover, the early maturing SAMNUT 21 fixed the highest (82 kg N ha-1) quantity of N 2 , while SAMNUT 11 (46 kg N ha-1) and 23 (31 kg N ha-1) were statistically similar and fixed the lowest N 2. SAMNUT 11 and 22 were, therefore, found to significantly record the highest nodule number and weigh and SAMNUT 21 fixed the highest N 2 , and hence the highest BNF, indicating their genotypic desirability in terms of N 2 addition to the soil environment, especially for subsequent crops.

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