Impact on Soil Organic C and Total Soil N from Cool- and Warm-Season Legumes Used in a Green Manure-Forage Cropping System

Annual forage legumes are important components of livestock production systems in East Texas and the southeastern US. Forage legumes contribute nitrogen (N) to cropping systems through biological N fixation, and their seasonal biomass production can be managed to complement forage grasses. Our research objectives were to evaluate both warm- and cool-season annual forage legumes as green manure for biomass, N content, ability to enhance soil organic carbon (SOC) and soil N, and impact on post season forage grass crops. Nine warm-season forage legumes (WSL) were spring planted and incorporated as green manure in the fall. Forage rye (Secale cereale L.) was planted following the incorporation of WSL treatments. Eight cool-season forage legumes (CSL) were fall planted in previously fallow plots and incorporated as green manure in late spring. Sorghum-sudangrass (Sorghum bicolor x Sorghum bicolor var. sudanense) was planted over all treatments in early summer after forage rye harvest and incorporation of CSL treatments. Sorghum-sudangrass was harvested in June, August and September, and treatments were evaluated for dry matter and N concentration. Soil cores were taken from each plot, split into depths of 0 to 15, 15 to 30 and 30 to 60 cm, and soil C and N were measured using combustion analysis. Nylon mesh bags containing plant samples were buried at 15 cm and used to evaluate decomposition rate of above ground legume biomass, including change in C and N concentrations. Mungbean (Vigna radiata L. [Wilczek]) had the highest shoot biomass yield (6.24 t DM ha-1) and contributed the most total N (167 kg∙ha-1) and total C (3043 kg∙ha-1) of the WSL tested. Decomposition rate of WSL biomass was rapid in the first 10 weeks and very slow afterward. Winter pea (Pisum sativum L. spp. sativum), arrow leaf clover (Trifolium vesiculosum Savi.), and crimson clover (Trifolium incarnatum L.) were the most productive CSL in this trial. Austrian winter pea produced 8.41 t DM ha-1 with a total N yield of 319 kg N ha-1 and total C production of 3835 kg C ha-1. The WSL treatments had only small effects on rye forage yield and N concentration, possibly due to mineralization of N from a large SOC pool already in place. The CSL treatments also had only minimal effects on sorghum-sudangrass forage production. Winter pea, arrow leaf and crimson clover were productive cool season legumes and could be useful as green manure crops. Mungbean and cowpea (Vigna unguiculata [L.] Walp.) were highly productive warm season legumes but may include more production risk in green manure systems due to soil moisture competition.

Efficiency of Legumes in Increasing Yam Yield under Sandy Ferrasol in the Forest Zone of Southwestern Côte d’Ivoire

The cropping system is based on traditional farming in rural areas. In this way, yields of some food crops like yam are very low considering their high need for nutrients. The nutrient-rich land is under high land pressure as it is occupied by cash crops such as oil palm and rubber at the expense of food crops and soil fertility is declining. The study was conducted in Grand-Lahou to assess the effect of organic matter provided by legumes in increasing yam yield. The randomized complete block design included four (4) treatments: Arachis hypogaea + yam association (T1), Acacia mangium + yam association (T2), Arachis + Acacia mangium + yam association (T3) and pure yam crop (T0). The parameters measured were: the soil nutrients content, the rate of mineralization of organic matter through the C/N ratio as well as the yield of yam through different techniques that allowed the objective of the study to be achieved. It was noted a slight improvement of nitrogen and organic carbon in all treatments with a higher value recorded in the T2 treatment. The C/N ratio decreased to 12 in all treatments compared to the control, which reflects a normal decomposition of the organic matter. Treatment T1 increased yam yield (8.4 t/ha) in contrast to treatments T2 (4.1 t/ha) and T3 (2.8 t/ha). Legume-based treatments T2 and T3 were associated with a significant decrease in yam yield, resulting in losses of −46.34% to −25.09%, while treatment T1 resulted in a gain of 28.57%. As a result, the treatments involving legumes contributed to normalizing the organic matter content of the soil. The simultaneous association of these two legumes led to a decrease in yam production, contrary to the treatment associating only groundnut.

Plant growth and soil microbial community structure of legumes and grasses grown in monoculture or mixture

A greenhouse pot experiment was conducted to investigate the in?uence of soil moisture content on plant growth and the rhizosphere microbial community structure of four plant species (white clover, alfalfa, sudan grass, tall fescue), grown individually or in a mixture. The soil moisture content was adjusted to 55% or 80% water holding capacity (WHC). The results indicated that the total plant biomass of one pot was lower at 55% WHC. At a given soil moisture, the total plant biomass of white clover and tall ...

Bowman-Birk inhibitors from legumes as colorectal chemopreventive agents

Aberrant functioning of serine proteases in inflammatory and carcinogenic processes within the gastrointestinal tract(GIT)has prompted scientists to investigate the potential of serine protease inhibitors,both natural and synthetic,as modulators of their proteolytic activities.Protease inhibitors of the Bowman-Birk type,a major protease inhibitor family in legume seeds,which inhibit potently and specifically trypsin-and chymotrypsin-like proteases,are currently being investigated as colorectal chemopreventive agents.Physiologically relevant amounts of Bowman-Birk inhibitors(BBI)can reach the large intestine in active form due to their extraordinary resistance to extreme conditions within the GIT.Studies in animal models have proven that dietary BBI from several legume sources,including soybean,pea,lentil and chickpea,can prevent or suppress carcinogenic and inflammatory processes within the GIT.Although the therapeutic targets and the action mechanism of BBI have not yet been elucidated,the emerging evidence suggests that BBI exert their preventive properties via protease inhibition;in this sense,serine proteases should be considered as primary targets in early stages of carcinogenesis.The validation of candidate serine proteases as therapeutic targets together with the identification,within the wide array of natural BBI variants,of the most potent and specific protease inhibitors,are necessary to better understand the potential of this protein family as colorectal chemopreventive agents.

Iron and Folate Contents of Tajik Legumes

Seven varieties of Tajik legumes and two Tajik snack type ready-to-eat (RTE) whole/split chickpeas were analyzed for iron in raw and cooked legumes and for naturally occurring folate content in cooked legumes. Iron was measured according to AACC method 40 - 41B. Folate contents were determined by microbiological (Lactobacillus casei subsp. Rhamnosus ATCC 7469) and high-performance liquid chromatography analysis utilizing a tri-enzyme treatment (pro-tease, α-amylase and conjugase). Folate derivatives of tetrahydrofolate, 5-formyl-tetrahydrofolate and 5-methyl- -tetrahydrofolate were identified and quantified. Iron content for Tajik legumes ranged from 5.52 to 13.27 mg/100 g for raw;2.81 to 4.12 mg/100 g for cooked and 4.37 and 4.76 mg/100 g for RTE chickpeas. The total folate content of cooked legumes ranged from 53 to 81 μg/100 g for beans;133 to 203 μg/100 g for peas, and from 39 to 22 μg/100 g for small and large lentils, respectively. The predominant form of folate in legumes was tetrahydrofolate, followed by 5-formyl-tetrahydrofolate and 5-methyl-tetrahydrofolate.

Methodological impact of starch determination on starch content and ileal digestibility of starch in grain legumes for growing pigs

Background： Grain legumes represent a valuable energy source in pig diets due to their high starch content. The present study was conducted to determine the content and apparent ileal digestibility（AID） of starch in different grain legume cultivars for pigs by means of both a polarimetric and enzymatic method for starch determination.Methods： Three experiments were conducted with six barrows each which were fitted with ileal T-cannulas. In total, 18 diets including six different cultivars of faba beans（Vicia faba L.） and peas（Pisum sativum L.）, five different cultivars of lupins（Lupinus luteus L., Lupinus angustifolius L.）, and one diet with a soybean meal（SBM） were fed.Results： The starch content of faba beans and peas was greater（P ＆lt; 0.05） when determined polarimetrically than enzymatically（438 vs. 345 g/kg dry matter（DM） in faba beans and 509 vs. 390 g/kg DM in peas, respectively）.Considerable lower starch contents were obtained in lupins and SBM, with 82 and 48 g/kg DM（analyzed polarimetrically） and ＆lt;1.1 and 3 g/kg DM（analyzed enzymatically）, respectively. Mean values for contents of neutral detergent fiber（NDF） and acid detergent fiber（ADF） in grain legumes ranged from 111 and 79 g/kg DM in peas to248 and 207 g/kg DM in lupins, respectively. Contents of condensed tannins in the colored flowered faba bean cultivars ranged from 2.1 to 7.4 g/kg DM. The AID of starch was greater（P ＆lt; 0.05） in pea than in faba bean cultivars,and using the polarimetric starch determination method resulted in greater（P ＆lt; 0.05） digestibility values than using enzymatic starch analysis（84 vs. 80% in faba beans and 86 vs. 83% in peas）. Moreover, AID of starch differed（P ＆lt; 0.05）within pea cultivars and starch digestibility in faba beans decreased linearly（P ＆lt; 0.05） as the content of condensed tannins increased. However, there was no relationship between contents of NDF and ADF and AID of starch in pea and faba bean cultivars.Conclusion： Both contents and AID of starch in grain legumes can vary as influenced by the analytical method used for starch determination. Generally, starch digestibility is greater when measured by polarimetric rather than enzymatic methods.

Phenotypic, Stress Tolerance and Plant Growth Promoting Characteristics of Rhizobial Isolates from Selected Wild Legumes of Semiarid Region, Tirupati, India

Rhizobia are vital for nitrogen input, fertility of soil and legume plant growth. Knowledge on rhizobial diversity from arid and semiarid areas is important for dry land agriculture in the context of climatic change and for economic utilization. This study provides morphological, biochemical, stress tolerance and plant growth promoting characteristics of fifteen rhizobial isolates from the nodules of same number of wild legumes and one isolate from cultivated Arachis hypogea from semi-arid region, Tirupati. The bacterial isolates were confirmed as rhizobia based on colony morphology and biochemical tests. Based on the colour change of YMA-BTB medium, eight isolates were identified as slow growers and six were fast growers. The isolates differed in growth pattern, colony morphology, antibiotic resistance at higher concentrations and uniformity in utilization of carbon and nitrogen sources. The isolates are tolerant to NaCl up to one percent, displayed normal growth at temperatures 28℃ - 30℃, at neutral pH and poor growth at pH 5and 9. The isolates varied in the production of EPS and IAA, positive for phosphate solubilization and siderophore formation. This functional diversity displayed by the isolates can be utilised for the legume crop production by cross inoculation.

Influence of Mineral Fertilization on the Capacity of Nodulation of Three Species of Legumes(Groundnut,Cowpea and Soybean)

Groundnut (Arachis hypogaea), cowpea (Vigna unguiculata) and soybean (Vigna radiata) are the main food legumes grown in Cote d’Ivoire and the localities of Haut-Sassandra. These legumes are highly valued for their nutritional, agronomic and economic value. Groundnut, cowpea and soybean are the main food legumes grown in Cote d’Ivoire and in the localities of Haut-Sassandra. On the other hand, Ivorian soils are characterized by a tendency towards acidification and a decrease in the content of nutrients such as phosphorus and nitrogen which have a direct impact on the products. To restore soil fertility, farmers use mineral fertilization. However, this fertilization has an influence on the nodulation of these legumes. The study took place at Jean Lorougnon University. We adopted a completely random experimental block device. The parameters measured included the number of nodules, the length and weight of the plant, the length and weight of the root system. Our results showed that mineral fertilization reduced the nodulation capacity of legumes. However, a small dose of phosphorus ( g) would be required for early growing legumes.

Estimation of N_2 Fixation by Some Legumes Using ^（15）N－Labelled Soil in Greenhouse Experiment

Pot experimeats were carried out to estimate N2 fixation by vetch, milk vetch, sickle alfalfa and broadbean in pure stand using a 15N-labelled soil. Winter wheat was used as the non-fixing control. The 15N-labelled soil used was prepared by growing corn-wheat-corn successively on a nearly organic-matter-free Xiashu loess supplemented with adequate amounts of (15NH4)aSO4, P, K and micronutrients, then incorporating these 15N-labelled plant msterials into the soil after each harvest, and allowing the plant materials to be decomposed aerobically for 410 d after incorporation of the plant material of the third crop. The 15N enrichment of wheat plant-N varied slightly with organs,with a maximum difference of 9.8%. Based on 15N enrichment of soil N inferred from the mean value of the 15N enrichment in different organs of wheat 79%-91% of total N in the tops and 67%-74% of total N in the roots of legumes studied were derived from atmosphere. Estimate by isotope dilution method was in good agreement with that by the conventional difference method provided values obtained by the latter were corrected for seed N, and also with that from the measurement of N accumulated in the tops of the legumes.

Agro-Ecological Adaptation and Participatory Evaluation of Multipurpose Tree and Shrub Legumes in Mid Altitudes of Sud-Kivu, D. R. Congo

Livestock is traditionally managed in mixed crop-livestock production systems in Sud-Kivu, D. R. Congo. Currently, livestock production is facing numerous constraints due to wars and insecurity in the country, with looting of animals, demographic pressure on natural resources, and lack of extension services. Multipurpose trees and shrubs with adequate forage quality could help overcome dry-season feed shortage. The objective of this research was to assess the agro-ecological adaptability of selected forage tree and shrub legumes combined with farmer participatory evaluation. The study was carried out at two distinct mid-altitude sites in Sud-Kivu. Trees and shrubs were planted randomly in eleven lines, with each species/accession consisting of nine plants split into three replications. Following a standardization cut after one year of growth, regular biomass harvests were performed every eight weeks during one year;Desmodium and Flemingia were cut at 0.5 m above soil surface, while Leucaena and Calliandra at 1 m. Before every harvest, plant height was measured and number of stems counted. Fresh leaf and stem biomass were weighted, sub samples dried and leaves analyzed for nutritive value. Results from agronomic evaluation show that Leucaena diversifolia ILRI 15551 and Leucaena leucocephala had the highest yield in the rainy season on fertile soil;during dry season, Leucaena diversifolia ILRI 15551 was superior. On poor soil, Flemingia macrophylla CIAT 17403 performed best in both seasons, however, its forage quality was relatively low. Forage tree and shrub legumes chosen by farmers were, in general, the same as those superior ones in agronomic evaluation.

Preparation of Dried Vegetarian Soup Supplemented with Some Legumes

The present work was aimed to prepare dried vegetarian soup supplemented with some legumes. Potatoes, hull-less barley flour, carrot, tomatoes, onion, garlic, salt, black pepper, coriander and cumin (served as F1) were used in combination with lentil, green pea and chickpea to formulate F2, F3, and F4, respectively. Chemical, physical, rheological and sensory evaluation was performed. The results indicated that supplementation with legumes significantly enhanced the nutritional characteristics, where the dried vegetarian soup mixtures had reasonable amounts of the required nutrients particularly, protein, carbohydrates, fats, Fe and Zn with good in vitro protein digestibility and mineral availability. Moisture content and water activity predicted the extended shelf-life and stability of the dried soup mixtures. The four resultant soup samples F1, F2, F3 and F4 had a noticeable viscosity pattern characterized by a non-Newtonian pseudoplastic flow behavior. Supplementation with legumes significantly (p ≤ 0.05) affects taste, color, flavor attributes and overall acceptability of the resultant soup samples. But, it had no significant effect on thickness and appearance. The results clearly demonstrated the usefulness of supplementing the dried vegetarian soup mixtures with legumes to enhance nutritional and technological quality of the resultant soup and lentil was the most valuable addition with the highest acceptability.

Testing Agro-Ecological Adaptation of Improved Herbaceous Forage Legumes in South-Kivu, D.R. Congo

In tropical african countries where livestock is either reared in herds on natural grasslands or individuallly tethered to herds on natural or spontaneous vegetation, the productivity is low, especially during the dry season. Using improved forages could play an important role in both enhancing livestock production and improving soil fertility and preventing from soil erosion. Eleven herbaceous forage legumes previously tested in tropical South America and South Asia by CIAT were tested in South-Kivu, D. R. Congo. Across sites, Stylosanthes guianensis, Desmodium uncinatum, Centrosema molle and Canavalia brasiliensis had a highest yield, nowhere Vigna unguiculata adapted. Differencial plant adaptation occured, e.g. Clitoria ternatea being well adaptated only in the midlands with good soils, where the mean of dry mater leaf yield was higher. Farmer evaluation emphazied overall biomass production with preference in the highlands, farmers chose Desmodium uncinatum, Canavalia brasiliensis and Lablab purpureus 21603 and in the midlands Stylosanthes guianensis 11995 and Lablab purpureus 22759. Farmer evaluation confirmed the best yield fit herbaceous forage legumes.

Morphological Variability of Neglected and Underutilized Legumes (NULs) Collection from Côte d’Ivoire

In order to characterize neglected and underutilized legumes seeds (NULs), prospection, collection and characterization were carried out in five administrative regions from Cote d’Ivoire. Two thousand and fifty-four accessions were collected. NULs cultivation is done mainly by women (88.1% compared to 11.9% of men). Productors distinguish 22 morphotypes of NULs based on seeds shapes, colors and patterns. Morphological traits of the collected morphotypes revealed a significant phenotypic polymorphism. Quantitative analyses showed a clear structure of accessions;three main groups were revealed. The first group contains accessions with large and thick seeds, but a low index shape opposite to group II with high index shape. Seeds of group III are characterized by small width and thickness, but a high shape index. Analyses of qualitative traits revealed five groups characterized by heterogeneous or homogeneous coloured integument, inked or elevated edge of hilum, presence or absence of eye.

Production and Nutritive Value of Shrub Legumes in West Timor, East Nusa Tenggara Province Indonesia

This study aimed to identify the potential of shrub legumes as protein feed in West Timor. Eight shrub legumes, i.e., Clitoria ternatea Q5455 （CT Q5455）, Clitoria ternatea millgara （CT millgara）, Centrosema pascuorum bundey （CP bundey）, Centrosema pascuorum molle （CP molle）, Macroptilium bracteatum juanita （MB Juanita）, Macroptilium bracteatum cadaarga （MB cadaarga）, Dolichos lablab （DL） and Stylossanthes seabrana （SS） were evaluated for their yield and nutritive value in Randomized Block Design. Each legume was cultivated in four plots of different soil fertility as block （5 ~ 5 m2 per plot）. Phosphorus （P） fertilizer was applied once just before planting at level of 50 kg ha~. Watering was done three times per week using sprinkler. The legumes were harvested at 120 days after planting （dap） in three sub-plots of 1 x 1 m2 size for their yield measurement. Samples of each legume was taken for Dry Matter （DM）, Organic Matter （OM）, Crude Protein （CP）, cellulose, hemi-cellulose and lignin content and in vitro DM, OM and CP digestibility test. Data were statistically analyzed using Genstat release 12.2. The results showed that the legumes showed significantly different （P 〈 0.01） in biomass yield. The highest biomass yield was shown by SS （6,739 kg DM ha-l; 6,120 kg OM ha1 and 1,224 kg CP hal） and the lowest was by DL （1,294 kg DM ha^-1; 1,157 kg OM ha^-1 and 242 kg CP ha^-1）. In general, there was no significant difference （P 〉 0.05） of DM digestibility of the eight legumes, except for DL which showed significantly highest （P 〈 0.01） DM and OM digestibility compared to the other.

Accelerating Grain Legumes Production in Nigeria： Prospects and Challenges

This paper reviews programs and projects that are elements of the strategy to boost crop production in general and grain legumes in particular in Nigeria. The objective is to bring to fore the neglect of grain legumes production in such strategies and for improved understanding of the need to implement grain legumes specific programs for enhanced food security in the country. The paper reiterates that grain legumes were neglected in most of the strategies for increased crop production which presented enormous challenges and reflects largely the inbalance in the policies for the attainment of food self-sufficiency and food security in the country The paper gives an overview of the programs and projects, and reviews the output of grain legumes during the period （1970-2007）. It submits that the activities of some research institutes and the presidential initiative on vegetable oil development program had positive impact on the output of legumes which is an added impetus for the need to establish grain legumes specific research institutes and programs for further productivity increases. Constraints identified by the paper include： poverty, storage systems, among others. It itemizes prospects and current challenges for grain legume crop sub-sector in Nigeria.

Cultivation of Perennial Herbaceous Legumes in Weed Management in Coffee Plantation on the Cerrado

The aim of this study was to evaluate the cultivation of perennial herbaceous legumes on weed control and yield of the coffee crop in the Cerrado. The experimental design was a randomized complete block with four replications. The 10 treatments tested in factorial 4 × 2 ＋ 2, were four legumes： forage peanut （Arachis pintoi）, hybrid Java （Macrotyloma axillare）, perennial soybean （Neonotonia wightii） and wild ground nut （Calopogonium mucunoides）; two forms in the interrows of coffee plants with two and three rows of legumes spaced by 0.50 m and 0.25 m, respectively; and two additional treatments consisted of hand weeding with hoe and chemical control with glyphosate. The hybrid Java and wild ground nut in the first year and the hybrid Java and perennial soybean in the second year, all followed by forage peanut, promoted lower density and biomass of the weeds. The wild ground nut in the first year and forage peanut in the second year showed higher soil cover. The hybrid Java had its highest biomass production in two years, and wild ground nut being higher in the first year. The cultivation of perennial herbaceous legumes promoted weed control without interfering in the productivity of the coffee crop.

Extrapolations on the Use of Rhizobium Inoculants Supplemented with Phosphorus (P) and Potassium (K) on Growth and Nutrition of Legumes

Land scarcity and poor farming management practices has resulted in to intensive agriculture which rendered most of the soil in sub Saharan Africa depleted in essential plant nutrients. High prices of chemical fertilizer are crucial bottleneck toward increasing production of legumes and other food crops in most countries found in sub-Saharan Africa. Nitrogen, phosphorus and potas-sium are among the most limiting nutrients for plant growth as they play different but crucial roles in the plant physiological processes. These macronutrients are fundamental components of cell building blocks including genes and chromosomes. This review intend to show the vital roles played by rhizobial inoculants supplemented with phosphorus and potassium in enhancing growth, yield, photosynthesis, nodulation, nutrient uptake and nitrogen fixation of legumes.

Formulation and Optimization of Constituent in Legumes-Based Milk Chocolate Fortified with Citrus Peel Powder

The present study was employed to optimize the process for development of legumes-milk based chocolate using peanut (PN) and yellow-pea (YP) milk using Response surface methodology (RSM). Different combinations of legumes-milk chocolate at various ratios of PN:YP milk with fixed concentration of other regular ingredients were prepared, and the finest combination (1:1) was selected on the basis of their sensory and nutritional properties. PN and YP milk, Jaggery (JG), Butter (BT), and Citrus Peel Powder (CPP) served as independent variables while the dependent variables were allocated to the regression equation to determine folic acid (R2 = 93.15) along with protein content (R2 = 93.11) and vitamin C (R2 = 90.57). The nutritional parameters such as Folic acid, Protein and Vitamin C content were found to be optimum in the milk chocolate. The optimized concentrations of PNM, YPM, JG, BT and CPP were found to be 5.0 ml, 5.5 ml, 18.1 g, 2.9 g and 0.53 g respectively. Addition of JG had an interactive effect on folic acid in YP milk (p < 0.05) and CPP shows a significant. Enhancement of vitamin C was perceived in legume based milk chocolate than the control chocolate due to supplement of CPP.

Elemental Analysis of Some Nigerian Food Legumes by <i>k_o</i>-ENAA and INAA

Samples of the food legumes, cowpeas (Vigna unguiculata), soya beans (Glycine max) and groundnuts (Arachis hypogaea) collected from rural farmers in four rural villages around Zaria, Nigeria were analysed for the concentrations of the major, minor and trace elements by the ko-ENAA and INAA methods. Irradiation and γ-ray counting were performed using the NIRR-1 and associated facilities. The NIST 1515 Apple leaves were used as the quality control material. The concentrations of the elements Se, Br and Rb were determined by ko-ENAA while those of Na, K, Zn, La, Br, Sm and Sc were determined in INAA in the food legumes. The concentrations of Zn found in all the legumes are within the limit specified in international guidelines. The concentrations of Se found in the food legumes are above the limit specified in international guidelines. The food legumes are good sources of the elements Na, K, Zn which can meet adequate dietary requirements provided the legumes are not refined. Bromine is not at toxic levels in the food legumes.

Impact of Crude Oil on Soil Nitrogen Dynamics and Uptake by Legumes Grown in Wetland Ultisol of the Niger Delta, Nigeria

The effects of crude oil on soil nitrogen dynamics and cycling in plant-soil ecosystems and its effect on the growth of legumes (Calopogonium mucunoides, Centrosema pubescens and Pueraria phaseolodes) grown in wetland ultisols were investigated. The test plants species were grown on wetland soil simulated with 0.35, 10.8, 20.5, and 50 g.kg-1levels of crude oil contamination. The results showed time and species dependent variation in mineral N content of the treated soils. The variation is indicative of significant interaction between the hydrocarbon content and plant species. Variations in microbial N and microbial C were similar and correlation between the microbial N and the total C (Organic matter (C) + hydrocarbon content (C)) in soil was highly significant (r = 0.96, n = 12, P ≤ 0.01). The presence of hydrocarbon contaminant widens the C:N ratio in soil and leads to more available N being immobilized by soil microorganisms, which reduces available N for plant uptake. This result implies that crude oil contamination significantly reduces N uptake by plants but increases N accumulation in soil microbial biomass. The findings show that N dynamics, transformation and cycling in soil are influenced by hydrocarbons and that the interactions between hydrocarbon content and plant species in contaminated soil are remarkable. The use of plant Centrosema pubescens with poultry manure or NPK fertilizer for bioremediation is more effective than that of Calopogonium mucunoides and Pueraria phaseoloides. However, the selective attributes of the various treatment approaches adopted here may be exploited for enhanced remediation of contaminated wetlands in the Niger Delta region of Nigeria.