A field experiment was conducted during the 2005/6 growing season to assess the effect of
Nitrogen is one of the most abundant elements on earth. However, it is one of the most limiting factors of growth and production of crops. Nitrogen can be utilized when it is reduced to ammonia by nitrogen fixation. It can be reduced by chemical fixation through industrial production and/or biological fixation involving microorganisms. Even in the presence of such process called biological nitrogen fixation, nitrogen is one of the usually deficient plant nutrients in soils. Despite its abundance in the atmosphere as a gas, it cannot be utilized directly by plants. Most plants utilize nitrogen in its ionic forms ammonium (
The increasing cost of fertilizers and their impact on the environment have forced people to look for other possible sources of plant nutrients. In this regard, nitrogen fixation which is a process by which elemental atmospheric nitrogen is changed to organic forms by biological nitrogen fixation both by symbiotic and asymbiotic microorganisms in soil has drawn much attention. The symbiotic nitrogen fixation is used to maximum advantage in case of leguminous crops. There is no doubt that specificity exists between rhizobialstrain and the legume, and compatibility between the two is essential for successful nodulation. This necessitates using specific cultures for different legumes. When growing a new legume species on a soil, it is necessary that the appropriate rhizobial culture be applied [
Soils usually lack
Cultivar variation affects levels of nitrogen fixation in many legume crop species, and in some crops particular combinations of strain and cultivar have been shown to be especially efficient at fixing nitrogen [ Study the effects of inoculated Determine the main and interaction effects of
The experiment was conducted on Nitisols of Bako ATVET College Campus Experimental field during the 2005-2006 growing season. Bako is a small town in West Shoa zone of Oromia region which is located at 09°06′ north latitude and 37°09′ east longitude. Its elevation is 1650 meters above sea level (masl). According to the climate data collected from 1998 to 2002, the total annual rainfall of the area ranges from 1040 to 1559 mm. Mean annual maximum temperature is 31°C and the minimum being 11.2°C. The mean relative humidity is 64%. The mean soil temperature at the depth of 50 cm is 23.3°C. The major soil types at Bako area are Nitisols according to the FAO/UNESCO or Alfisols according to USDA soil classification systems. These soils are well-drained reddish brown in color and slightly to moderately acidic in reaction with surface soil pH (H2O) ranging from 5.3 to 6.5 [
The Bako area is well known for its maize production. A number of improved maize varieties, well-known throughout the country, were released by the Bako Agricultural Research Center. It is characterized by mixed crop-livestock farming system, encompassed by the Gibe River and with abundant natural vegetation, and grass lands [
The study enhanced a factorial combination of two strains of
Land preparation was done following the conventional practice to make the field suitable for planting. Chemical fertilizer as DAP at 100 kg/ha was applied at planting which supplied 18 kg nitrogen/ha as starter dose and 20.2 kg Phosphorous/ha. Then the land was leveled and divided into blocks and individual plots. The size of each plot was 3.2 × 4 m (12.8 m2). The plots were kept 0.5 m apart with 1 m spacing between blocks. Canals were prepared around each plot making the plots beds.
Carrier-based inoculant of each strain, obtained from NSRC, was applied at the rate of 10 g inoculant/kg seed [
Five plants were sampled randomly from the second border rows of each plot at midflowering (50% flowering). The whole plant was carefully uprooted using a spade so as to obtain intact roots and nodules for nodulation parameters and dry weight of plants. Uprooting was done by exposing the whole-root system to avoid loss of nodules. The adhering soil was removed by washing the roots with intact nodules gently with water over a metal sieve. The same five plants from each plot were used to rate nodulation and to record number of nodules per plant, nodule volume per plant, and nodule dry weight.
Out of the total number of plants uprooted from a treatment, the number of plants showing tap root nodulation (
After calculation of nodulation rating, the number of nodules per plant was determined by counting the number of nodules from all the five uprooted plants per plot and then averaged as per plant. To determine nodule volume, the nodules of the above five plants of each plot were collected carefully and immersed in a 50 mL capacity plastic cylinder which was filled up to 30 mL with water. The volume of water displaced by the nodules obtained from the five plants was recorded, and the average was considered as nodule volume per plant. Finally, the nodules collected from the five plant samples from each plot were pooled, and their dry weight was determined by drying the nodules at 70°C to constant weight, and the dry weight was reported as mg/plant.
Five plants were sampled randomly at maturity from each plot, pods were counted for all the five plants, and the average value was reported as number of pods per plant. The number of seeds per pod was determined from 20 pods randomly sampled from the five sample plants, and the average was reported as number of seeds per pod. The number of plants per plot was recorded at harvesting from the central six rows, and the mean was computed and used for the analysis of final plant stand.
Soybean plants were harvested from each plot at physiological maturity leaving the border rows and 0.5 m row length on every end of each rows. Seed yield was obtained by adjusting the moisture level to 10% according to the formula indicated by Abebe [
The weights of thousand seeds randomly counted from the seeds of each plot maintaining the seed moisture content at 10% were reported as thousand seeds weight. Whole plants, including above-ground parts and roots after separating the nodules, sampled from each plot at midflowering were pooled together and oven dried at 70°C to constant weight. The average of five plants was reported as dry weight per plant.
After recording the seed yield, for each plot, five plants were taken randomly from the central rows and oven dried at 70°C to constant weight to determine above-ground dry matter yield. Finally, the total above-ground biomass yield was obtained by adding the seed yield and above-ground dry matter yield. Harvest index was calculated as a ratio of seed yield to above-ground biomass yield.
The plant samples taken at midflowering from each plot were oven dried at 70°C to a constant weight, ground to pass a 1 mm sieve, and analyzed for their nitrogen concentrations using the modified Kjeldahl method as described by Jackson [
Representative seed and straw samples were taken separately from each replication and composited treatment wise. Materials were separately air dried and then oven dried at 70°C to a constant weight, ground to pass a 1 mm sieve and were saved for laboratory analysis of seed and straw nitrogen concentrations. The nitrogen in the plant parts was determined by the modified Kjeldahl method as described by Jackson [
The data were subjected to analysis of variance following the standard procedure given by K. A. Gomez and A. A. Gomez [
Soil analysis of the experimental field has shown that the soil was moderately acidic in reaction (pH = 5.5) and sandy clay loam in texture (Table
Surface (0–30 cm) soil physical and chemical properties of the experimental site.
Particle size distribution (%) | Textural class | pH (1 : 2.5 H2O) | OC (%) | TN (%) | AP (ppm) | CEC (Cmol (+)/kg) | PBS | ||
---|---|---|---|---|---|---|---|---|---|
Sand | Silt | Clay | |||||||
47 | 20 | 33 | SCL | 5.5 | 1.88 | 0.14 | 14.82 | 15.60 | 54 |
SCL: sandy clay loam; OC: organic carbon; TN: total nitrogen; AP: available phosphorous; CEC: cation exchange capacity; PBS: percent base saturation.
Uninoculated control did not show any nodule indicating the absence of native rhizobial population specific to soybean. Soybean varieties, irrespective of rhizobial strain inoculation, did not vary significantly in relation to nodulation rating. Nodulation rating was not significantly affected by the interaction effect of soybean variety and rhizobial strain (Table
Main effects of soybean varieties and
Treatment | Nodulation rating | Number of nodules (no./plant) | Nodule volume (mL/plant) | Nodule dry weight (mg/plant) |
---|---|---|---|---|
Variety | ||||
| ||||
Jalele |
2.38 |
4.36 |
0.29 |
68.89 |
| ||||
Strain | ||||
| ||||
Uninoculated |
0.00b |
0.00b |
0.00b |
0.00b |
| ||||
Significance | ||||
| ||||
Variety | NS | NS | NS | NS |
Strain |
|
** | ** | ** |
Variety × strain | NS | * | NS | * |
| ||||
CV (%) | 22.19 | 12.66 | 6.62 | 25.18 |
NS, *, **: nonsignificant or significant at
As it is evident from the data presented in Tables
The interaction effect of soybean varieties and
Treatments | Number of nodules (no./plant) | Nodule dry weight (mg/plant) |
---|---|---|
Variety |
||
| ||
Jalele (uninoculated) |
0.00c |
0.00d |
| ||
Variety × strain | ||
| ||
TAL 378 + Jalele |
0.07c |
0.00d |
TAL 379 + Cheri | 13.47a | 193.33ab |
TAL 378 + ET-Y | 0.33c | 12.67c |
TAL 379 + ET-Y | 9.60b | 140.00b |
Means within a column followed by the same letter(s) are not significantly different.
The interaction between soybean varieties and rhizobial strains was found significant in relation to number of nodules (Table
Analysis of variance has shown that the nodule volume per plant was not affected significantly by the main effect of the soybean varieties. However, it was significantly (
The dry weight of nodules was not affected significantly (
Nodule dry weight was significantly (
The dry matter production at midflowering was significantly (
Main effects of soybean varieties and
Treatment | Dry matter (g/plant) | Nitrogen uptake (mg/plant) |
---|---|---|
Variety | ||
| ||
Jalele | 19.03b | 654.91b |
Cheri | 17.22b | 644.25b |
Ethio-Yugoslavia | 23.75a | 872.22a |
| ||
Strain | ||
| ||
Uninoculated | 16.78b | 555.62b |
TAL 378 | 17.10b | 578.90b |
TAL 379 | 26.12a | 1036.86a |
| ||
Significance | ||
| ||
Variety | ** | ** |
Strain | ** | ** |
Variety × strain | NS | NS |
| ||
CV (%) | 13.44 | 15.35 |
NS, **: nonsignificant or significant at
The main effect of inoculation of rhizobial strains also showed significant (
The main and interaction effects on nitrogen uptake due to soybean varieties and rhizobial strains are presented in Table
The main effect of soybean varieties alone was significant in relation to number of pods per plant. EthioYugoslavia recorded significantly higher number of pods as compared to Jalele although it was statistically at par with Cheri. The number of pods per plant was also significantly (
Main effects of soybean varieties and
Treatment | NPP (Nr.) | NSP (Nr.) | FPS (Nr.) | SY (kg/ha) | TSW (g) |
---|---|---|---|---|---|
Variety | |||||
| |||||
Jalele | 77.36b | 2.21 | 162.44 | 2560.19b | 212.81a |
Cheri | 100.62a | 2.07 | 161.56 | 3416.67a | 204.07a |
Ethio-Yugoslavia | 103.82a | 2.18 | 157.89 | 3044.75ab | 181.41b |
| |||||
Strain | |||||
| |||||
Uninoculated | 75.71b | 2.09b | 161.33 | 2580.25b | 190.54b |
TAL 378 | 81.16b | 2.07b | 159.67 | 2487.65b | 191.36b |
TAL 379 | 124.93a | 2.30a | 160.89 | 3953.71a | 216.39a |
| |||||
Significance | |||||
| |||||
Variety | ** | NS | NS | ** | ** |
Strain | ** | ** | NS | ** | ** |
Variety × Strain | NS | NS | NS | NS | NS |
| |||||
CV (%) | 15.19 | 6.01 | 2.84 | 15.65 | 7.00 |
NS, **: nonsignificant or significant at
NPP: number of pods per plant, NSP: number of seeds per pod, FPS: final plant stand, SY: seed yield, TSW: thousand seed weight, Nr: number.
Although the number of seeds per pod was not significantly different among the varieties, it was affected significantly (
The summarized results for the final plant stand are presented in Table
Seed yield was affected significantly (
Thousand seed weight was found to be affected significantly (
The main effect of varieties did not show significant effect on the above-ground dry biomass yield (Table
Main effects of soybean varieties and
Treatment | BY (ton/ha) | HI | TNU (mg/plant) |
---|---|---|---|
Variety | |||
| |||
Jalele | 12.44 | 0.204b | 1783.71b |
Cheri | 12.64 | 0.268a | 2106.29a |
Ethio-Yugoslavia | 11.68 | 0.262a | 2055.27ab |
| |||
Strain | |||
| |||
Uninoculated | 10.48b | 0.248 | 1580.20b |
TAL 378 | 10.75b | 0.230 | 1664.96b |
TAL 379 | 15.53a | 0.257 | 2700.12a |
| |||
Significance | |||
| |||
Variety | NS | ** | ** |
Strain | ** | NS | ** |
Variety × strain | NS | NS | NS |
| |||
CV (%) | 10.22 | 12.77 | 10.14 |
NS, **: nonsignificant or significant at
BY: above-ground dry biomass yield, HI: harvest index, TNU: total nitrogen uptake at maturity.
Harvest index was observed to be significantly (
The total nitrogen uptake by soybean plants at maturity was significantly (
Successful nodulation of leguminous crops by
The total nitrogen value is in the low range of nitrogen content as per the criteria developed by Landon [
It seemed apparent from the responses obtained that the moderately acidic soil pH did not pose major problems on the bacterial strains, the soybean plant, and their association. Although the presence of high amount of total nitrogen in the rhizosphere is known to exert an adverse effect on the nodule nitrogen fixation of legumes [
Legumes have a high internal phosphorous requirement for their symbiotic nitrogen fixation. Singleton et al. [
The inability of TAL 378 to produce nodules on soybean roots could be attributed to incompatibility of this strain with soybean varieties used in the present study. Kuykendall et al. [
The results of the present study have indicated that it is important to promote the appropriate use of biofertilizers through national fertilizer programs. Efforts should be made, wherever possible, to introduce inoculation technology to the farming community. More research based on standard methods needs to be undertaken to assess the contribution of nitrogen-fixing plants to the overall nitrogen budget. The use of rhizobial inoculants is at its infancy in Ethiopia, and so far it is not one of the research priorities of Agricultural Research Institutions in the country. Rhizobial inoculants are not locally available, and farmers are not aware about this new technology. Therefore, more efforts need to be done to popularize this cheap and ecofriendly technology among resource poor farming community of the nation. For an alternative use, TAL 379 can be recommended for soybean inoculum production.
The funding for this study was provided by the Ministry of Agricultural and Rural Development. The authors thank all those who gave us constructive ideas in shaping this manuscript. However, only the authors did participate in the conduction of the study, data collection and interpretation, and article preparation.