A. Ayanaba

Response of cowpea (Vigna unguiculata) to inoculation with VA-mycorrhizal fungi and to rock phosphate fertilization in some unsterilized Nigerian soils.

SummaryThe effects on cowpea of inoculation with vesicular-arbuscular (VA) mycorrhizal fungi and rock phosphate (RP) fertilization were studied in pots using Alagba and Araromi series soils and in the field on Alagba, Apomu and Egbeda series soils. Inoculation of the plants with VA-mycorrhizal fungi caused very rapid infection of the roots. A higher per cent mycorrhizal infection was maintained during subsequent plant growth in the field. RP application reduced the degree of infection without affecting plant growth in the field and in pot experiments. Nodulation, nitrogen fixation and utilization of RP were increased by inoculation with mycorrhizal fungi in the pot experiments but not in the field experiments. In the pot experiments, inoculated plants supplied with RP flowered earlier, and took up more phosphorus than either inoculated plants without RP or uninoculated plants. The largest response to inoculation in terms of shoot dry matter, nodule yield and nitrogen content of shoots was obtained in Alagba soil under both pot and field conditions.

Nitrogen fixation of field-inoculatedLeucaena leucocephala (Lam.) de Wit estimated by the15N and the difference methods

The amount of nitrogen fixed byLeucaena leucocephala (Lam.) de Wit was assessed on an Alfisol at the International Institute of Tropical Agriculture located in southwestern Nigeria. Estimated by the difference method, nitrogen fixation of leucaena inoculated with Rhizobium strain IRc 1045 was 133 kg ha−1 in six months. Inoculation with Rhizobium strain IRc 1050 gave a lower nitrogen fixation of 76 kg ha−1. Fertilization with 40 and 80 kg N ha−1 inhibited nitrogen fixation by 43–76% and 49–71%, respectively. Estimates with the15N dilution method gave nitrogen fixation of 134 kg ha−1 in six months when leucaena was inoculated with Rhizobium strain IRc 1045 and 98 kg ha−1 for leucaena inoculated with Rhizobium strain IRc 1050. This nitrogen fixation represented 34–39% of the plant nitrogen. Inoculated leucaena derived 5–6% of its nitrogen from applied fertilizer and 56–54% from soil.

Mineral N effects on cowpea and soybean crops in a Nigerian soil

SummaryIn a Nigerian soil depleted in available N, fertilizer-N enriched in15N was applied at 25 and 100 kg N/ha to crops of four cowpea and two soybean cultivars. Soil-N availability was estimated with three non-fixing crops, non-nodulating soybean, maize and celosia. With sequential harvests we examined the development of the fixing crops, as well as their nodulation profiles and acetylene reduction activities, and the patterns obtained were correlated with uptake of mineral-N. At low levels of mineral-N, excellent nodulation (up to 580 mg dry weight/plant) and very high acetylene reduction activities (up to 208 μmoles/plant/h) were recorded. Although fertilizer-N utilizations were low, 12% and 28% at 25 and 100 kg N/ha respectively, the lower application had a transient adverse effect on nodule development and the higher application had a long-term adverse effect on nodule formation, nodule development and acetylene reduction activity. Cowpea nodule mass reached maximum levels at early pod-fill except at 100 kg N/ha at which it continued to increase into late podfill. In contrast, soybean nodulation did not peak at any level of N but increased into late pod-fill.

Nitrogen contribution of Leucaena/Rhizobium symbiosis to soil and a subsequent maize crop

The nitrogen contribution from the shoot and root system of symbiotically grown leucaena was evaluated in a field experiment on an Alfisol at IITA in Southern Nigeria. Maize in plots that received prunings from inoculated leucaena contained more N and grain yield was increased by 1.9 t.ha.−1. Large quantities of nitrogen were harvested with leucaena prunings (300 kg N ha−1 in six months) but the efficiency of utilization of this nitrogen by maize was low compared to inorganic N fertilizer (ammonium sulphate) at 80 kg N ha−1. Maize yield data indicated that nitrogen in leucaena prunigs was 34 and 45% as efficient as 80 kg N ha−1 of (NH4)2SO4 for uninoculated and inoculated plants with Rhizobium IRc 1045, respectively. In plots where the prunings were removed, the leaf litter and decaying roots and nodules contributed N equivalent of 32 kg ha−1. Twenty-five kg ha−1 was the inorganic N equivalent from nitrogen fixed symbiotically by leucaena when inoculated with Rhizobium strain IRc 1045. Application of prunings from inoculated leucaena resulted in higher soil ogranic C, total N, pH and available NO3.

The efficacy of soybean inoculation on acid soil in tropical Africa

SummaryThe efficacy of inoculating soybean cvs. TGm294-4 and TGm80 in an acid soil (pH 4.6, water) was studied in a field trial in Nigeria.Rhizobium japonicum strains CB1809strr and 46spcr which had been selected for symbiotic competence in the acid soil were used as inocula. Other treatments included no inoculation, combined nitrogen (150 kg N ha−1) and lime (1 t ha−1).Plants grown in acid soil without inoculation and lime had very few nodules, were nitrogen deficient and grain yields were poor (0.3–0.4 t ha−1). Yield responses to combined nitrogen were generally small due to fertilizer loss through leaching. Inoculation greatly increased nodulation, shoot dry matter and shoot N%; grain yields were between 1.6 and 2.0 t ha−1. Lime improved all harvest measurements in the uninoculated and nitrogen treatments but not in the inoculated treatments.In a duplicate trial without lime on near-neutral soil, similar inoculation responses were obtained at 6 weeks. However, at final harvest there were no significant differences in grain yield between treatments due to late, effective nodulation by unidentified strains in the uninoculated treatments.Assays for strain identity confirmed the successful establishment of the inocula in both soils, with 100% of nodules from inoculated plants containing an introduced strain.

Effectivity of indigenous rhizobia for nodulation and early nitrogen fixation with Leucaena leucocephala grown in nigerian soils

Abstract Rhizobium strains isolated from Leucaena leucocephala . Sesbania rostrata , S. grandiflora , S. punctata , Tephrosia vogelii . Acacia albida and Vigna unguiculata growing in Nigerian soils were characterized and tested for their ability to nodulate and fix atmospheric nitrogen with L. leucocephala . Isolates from L. leucocephala , S. rostrata . S. grandiflora and S. punctata were fast-growing and acid producers whereas those from A. albida , T. vogelii and V. unguiculata were slow-growing and alkali producers. Some of these isolates grew in the presence of 500 μg streptomycin ml −1 . The effectivity of the rhizobia isolates on L. leucocephala was tested in Leonard jars. Isolates from all plant species except those from S. grandiflora and V. unguiculata nodulated L. leucocephala but a wide range of effectiveness was observed. Based on this experiment the ten most promising rhizobia were screened for effectiveness in potted soils collected at IITA, Ibadan (transition forest savanna), and at Fashola (savanna, 70 km north of IITA). Establishment of L. leucocephala was poor in soils without previous history of L. leucocephala cultivation due to the presence of only few native leucaena rhizobia ( −1 soil). Rhizobium isolates IRc 1045 and IRc 1050 obtained from L. leucocephala grown at Fashola and IITA were found to be the most effective rhizobia on this host. In addition to their effectiveness and competitiveness they survived well in the field 1 year after their establishment.

Growth and yield responses of cowpea and maize to inoculation withGlomus mosseae in sterilized soil under field conditions

SummaryThe effects of inoculation of cowpea and maize withGlomus mosseae and sowing into field soil fumigated with formalin are reported. Root infection was significantly, though temporarily, decreased and grain yield increased, by sterilization. Inoculation increased root infection, shoot yields, P contents and grain yield.

Response of Leucaena/Rhizobium symbiosis to mineral nutrients in southwestern Nigeria

Pot and field experiments carried out at the International Institute of Tropical Agriculture (IITA) and at Fashola, Southwestern Nigeria, examined the effect of inoculation and N, P and micronutrients on nodulation and growth ofLeucaena leucocephala (Lam.) de Wit. In pot studies all parameters measured, except the percentage of nitrogen in shoots, were improved by inoculation, nitrogen and phosphorus. Micronutrients increased only nitrogen and allantoin contents. Interactions between inoculation and P, N and micronutrients on nodulation and growth of leucaena were observed. The effect of inoculation and fertilization with phosphorus or micronutrients was further investigated in field experiments. Establishment of uninoculated and unfertilized leucaena was poor at both locations due to low soil fertility and the presence of only a few native leucaena rhizobia. At one site, only inoculated plants were nodulated, while at the other, all plants produced nodules. Shoot dry weight, total nitrogen and phosphorus of inoculated plants were statistically equal to nitrogen-fertilized plants. Uninoculated plants were stunted. Generally, micronutrients did not influence nodulation, total nitrogen or growth of leucaena. They had only a positive effect on nitrogenase activity. Phosphorus increased total nitrogen and phosphorus uptake and plant growth. A 75% increase in shoot dry weight was obtained when 80 kg P ha−1 was applied to inoculated leucaena with Rhizobium strain IRc 1045. Inoculated plants contained more allantoins than uninoculated ones but no significant correlation was found between these compounds and other parameters of N fixation.

Effect of seed inoculation and preinfecting cowpea (Vigna unguiculata) withGlomus mosseae on growth and seed yield of the plants under field conditions

SummaryThe effects of inoculation withGlomus mosseae and method of planting on the performance of two cowpea cultivars were studied in field experiments on a sandy loam soil. Inoculation increased the percentage of infected roots, shoot dry matter and nodule yield of both cvs. TVx 1836-44G and VITA-4. Whether seedlings were transplanted or seeds were directly sown, dry matter production and nodule yield of both cultivars were not significantly affected; transplanted VITA-4 had greater per cent root infection than plants from directly sown seed. Seed yield was not affected by method of planting. The results indicated that the initial advantage of transplanted plants was not important in determining yield.

Nodulation and growth ofLeucaena leucocephala (Lam.) de Wit as affected by inoculation and N fertilizer

Leonard jar, pot and field experiments examined the effects of inoculation and the influence of nitrogen fertilizer on nodulation, nitrogen fixation and growth ofLeucaena leucocephala (Lam.) de Wit at IITA, Ibadan, Nigeria. Leucaena responded to both inoculation and/or nitrogen application. Shoot growth and total N and P of inoculated plants were comparable to those of the highest N treatment, and the values were about 55% greater than those of uninoculated ones. Field data indicated that toal N yields of inoculated leucaena were increased by 50% with 40 or 80 kg ha−1 of N fertilizer. However, N fertilizer depressed N fixation by 56% as was expected from nodule mass data. N-fixation was delayed for about 8 weeks in the plots without N. Application of small amounts of N starter (20 ppm) proved to be beneficial to satisfy the plant need during the early stage of leucaena growth. The rhizobial strains IRc 1045 and IRc 1050 were effective, competitive and survived well in the field one year after their establishment.