Many cowpea varieties (
Cowpea (
The research was conducted at the Cinzana Agronomic Research Station, SRAC (13° 15′ N° 5° 57′ W, altitude 281 m). The Cinzana Station is located in the Rural Commune of Cinzana, at 5 km far from Cinzana village situated 45 km from Segou city on the way Segou-Mopti.
The climate is characterized by an interannual variability of rainfall, turbulent high intensity, and irregular intraseason rains. The rainy season begins in June-July and ends in September-October. More than half of the rain usually falls in July-August (Figure
Rainfall in 10- or 11-day periods at Cinzana Agronomic Research Station (1972–2001), 2007, 2008, and 2009.
The research was conducted on a leached tropical ferruginous soil with spots and concretions [
The plant material used consisted of three (3) varieties of cowpea and one variety of pearl millet. The three cowpea varieties were IT89KD-374 (65–70 days) from IITA (International Institute of Tropical Agriculture), CZ1-94-23-1 (75–80 days), and CZ11-94-5C (65–70 days) from IER (Institut d’Economie Rurale), which is the National Agronomic Research Institute of Mali. These varieties are semiprostrate and semideterminate cowpea varieties. The variety of millet used was NKO × Toroniou C1 (110 days) from IER.
The experiment was conducted in two series (2007-2008; 2008-2009) based on a complete randomized blocks design, 4 replications. Treatments consisted of a factorial combination of 3 cropping systems and 3 cowpea varieties. The 3 cropping systems consisted of the millet/cowpea intercropping in alternate rows (1 row millet/1 row cowpea), the millet/cowpea intercropping in interhills (2 hills mil/1 hill cowpea) and cowpea-millet rotation.
The 3 cowpea varieties were IT89KD-374, CZ1-94-23-1, and CZ11-94-5C. Plot size was 7.5 m × 8 m = 60 m2. Soil was prepared by ridging to the tractor at 0.75 m spacing between ridges or 10 ridges of 8 m long. Seedings were made manually on the ridges. A dose of 300 kg ha−1 Tilemsi natural rock phosphate (PNT) was applied in 2008 on all of the plots of the first experiment and at the beginning of the 2009 rainy season for the second.
Cowpea in monocropping system was sown on top of ridges by hand at 0.40 m between the hills or 0.75 m × 0.40 m and thinned at two plants per hill after crop emergence (66 667 plants ha−1). In the millet/cowpea intercropping alternating rows (1 millet/1 cowpea), the spacing of the cowpea seedlings was 0.40 m between the hills, or 1.50 m × 0.40 m and thinned at two plants per hill after crop emergence (33 333 plants ha−1). In interhills system (2 hills millet/1 hill cowpea), cowpea was sown at 1.60 m between the hills of cowpea or 0.75 m × 1.60 m and thinned to two plants per hill after crop emergence (16 667 plants ha−1). The cowpea was sown to the lifting (raising) of millet in the interhills cropping system (2/1), while it was sown simultaneously with the millet in the alternating rows cropping system (1/1). Weedings were done manually as needed using hoe and mounded at the millet growth stage.
Crop symbiotic potential has been characterized through the study of cowpea nodulation and the assessment of the rate of mycorrhizal colonization of the roots of the two crops (millet and cowpea). Nodules harvesting was carefully done by digging up 2 hills of 2 plants in different basic plot points. All of the nodules collected were washed. The total number of nodules was evaluated by counting. The size of the nodules has been measured with a slide calipers and their efficiency estimated by dissection and observation of the presence of corresponding to leg hemoglobin coloration (reddish). Nodules weight dry was determined by weighing after drying in an oven at 65°C.
Mycorrhizal roots were collected in the 45th day after emergence and flowering stage. They were washed in tap water to remove soil and dried in the shade. In the laboratory, roots were treated with 70% alcohol and then rinsed with tap water to eliminate alcohol. Then, were dipped in 10% KOH at 80°C for 30 min followed by a bath Marie at 80°C for 10 min to eliminate the cytoplasmic contents of root cells to better reveal the mycorrhizal structures.
Mycorrhizal fungi were highlighted directly on root fragments after staining in a 0.05% Trypan blue solution for 30 min at 80°C and microscopy observation. Phillips and Hayman [
Assessments of the promising results obtained on station with CZ11-94-5C and IT89KD-374 cowpea varieties were conducted in farmers’ fields in Cinzana Rural commune during the 2010 growing season. Eight villages of the municipality were chosen based on their accessibility (roadside). Farmers’ choice was made on voluntary basis to conduct the test.
Two improved cowpea varieties CZ11-94-5C and IT89KD-374 and the local millet variety of the collaborating farmer were used. The two cowpea varieties are short maturity types (65–70 days) as previously.
The experimental design used was plots of observations in scattered replications. Each farmer had a block of complete treatments and therefore was a replication. Six (6) treatments were compared: sole crop of CZ11-94-5C (T1), sole crop of IT89KD-374 (T2), millet/CZ11-94-5C intercropping (1 row/1 row) (T3), millet/IT89KD-374 intercropping (1 row/1 row) (T4), millet/CZ11-94-5C intercropping (2 rows/1 row) (T5), millet/IT89KD-374 intercropping (2 rows/1 row) (T6). Plots size was 400 m2 (20 m × 20 m). Cowpea plots did not receive fertilizer. Mixtures of 50 kg DAP (diammonium phosphate) and 50 kg ha−1 of urea were applied on the millet rows.
The test was conducted in nineteen farmers’ fields. The objective was to evaluate at farmer’s level the performance of nodulation and the two cowpea varieties (CZ11-94-5C and IT89KD-374) yields in three cropping systems.
The seedings have been carried out between July 25 and August 03, 2010.
The rainfall distribution graph (Figure
At the flower buds stage, highly significant differences (
Cowpea nodules number (nodules/plant) and efficiency as affected by cropping system and cowpea variety at flower buds stage at Cinzana Agronomic Research Station, 2007 and 2008.
Treatments | Flower buds stage | |
---|---|---|
Nodules number (nodules/plant) | Efficient nodules (%) | |
Years | ||
Year 1: 2007 | 41a | 77 |
Year 2: 2008 | 30b | 76 |
| ||
Cropping systems | ||
Millet/cowpea intercropping (1 row/1 row) | 47a | 78ab |
Millet/cowpea intercropping (2 hills/1 hill) | 19c | 69b |
Cowpea sole crop | 40b | 81a |
| ||
Cowpea varieties | ||
V1: IT89KD-374 | 36 | 86a |
V2: CZ1-94-23-1 | 32 | 62b |
V3: CZ11-94-5C | 37 | 80a |
| ||
Effect |
|
|
Year (Y) | <0.01 | — |
Cropping system (S) | <0.01 | 0.03 |
Year × cropping system (Y × S) | 0.07 | — |
Cowpea variety (V) | 0.06 | <0.01 |
Year × variety (Y × V) | <0.01 | 0.30 |
Cropping system × cowpea variety (S × V) | — | — |
Year × cropping system × variety (Y × S × V) | 0.13 | — |
Coefficient of variation (%) | 22.78 | 21.21 |
Means followed by the same letters in the same column for each parameter are not significantly different (
Nodules dry weight (mg/plant) as affected by year × cropping system × cowpea variety interactions effects (
Cropping system effects on efficient nodule numbers (
Average mycorrhization rates of cowpea and millet were at the same order of magnitude at flower buds (30–40%) and flowering stages (40–50%). Cropping systems and cowpea varieties did not have a significant influence (
The three-way interaction between year × cropping system × cowpea variety was highly significant (Figure
Cowpea plants density (plants/ha) as affected by year × cropping system × cowpea variety interactions effects (
Crops yields: (a) cowpea grain as affected by cropping system × cowpea variety interactions effects (
Multiyear analysis of grain and above-ground total biomass dry yields of millet showed high significant interactions between year, cropping system, and cowpea variety (
The differences between nodules numbers were highly significant (
Cropping system effects on cowpea nodules number (nodules/plant), nodules dry weight (mg/plant) at bloom stage, and cowpea and millet grain yield (kg/ha) in farmers’ fields in 2010.
Cropping systems | Cowpea nodules number by plant | Cowpea nodules dry weight (mg/plant) | Cowpea grain yield (kg/ha) | Millet grain yield (kg/ha) |
---|---|---|---|---|
Farmers’ control | No* | No* | No* | 465a |
Cowpea variety CZ11-94-5C sole crop | 22a | 160 | 730a | No* |
Cowpea variety IT89KD-374 sole crop | 16b | 117 | 605b | No* |
Millet/CZ11-94-5C alternate rows intercropping (1 row/1 row) | 20ab | 140 | 390c | 335b |
Millet/IT89KD-374 alternate rows intercropping (1 row/1 row) | 15b | 119 | 340cd | 350b |
Millet/CZ11-94-5C alternate rows intercropping (2 rows/1 row ) | 23a | 163 | 280cd | 485a |
Millet/IT89KD-374 alternate rows intercropping (2 rows/1 row) | 17b | 139 | 245d | 495a |
Effect |
|
|
|
|
Cropping system | <0.01 | 0.09 | <0.01 | <0.01 |
Coefficient of variation (%) | 37.02 | 45.21 | 42.17 | 21.41 |
Means followed by the same letters in the same column are not significantly different (
No*: no millet.
Cropping system had high significant effect (
The results showed highly significant effects of cropping system on cowpea nodules number and nodules dry weight whatever the stage of observation with three-way high significant interaction of year, cropping system, and cowpea variety. These results were not supported by the finding of Kombiok et al. [
The differences between cropping systems effects on cowpea nodulation can be explained by differences in plants density of the different systems. These results were consistent with those of Makoi et al. [
The results of the main parameters for symbiotic fixation (nodulation number and weight and the efficiency of nodules) showed that the variety CZ11-94-5C has the best symbiotic potential.
Mycorrhization rates increased from 45th day after emergence to the flowering, whatever the cropping system was in agreement with the observations of Bagayoko [
The best cowpea grains yields in sole crop (Figure
Under low plants density, cowpea roots accumulate more nutrients, including mineral N, which inhibits the activity of nitrogenase [
Increase in millet grains yield in rotation is consistent with the results obtained by different authors [
Rhizobium associated with cowpea in different cropping systems may also explain the results. Some specific strains associated with cowpea varieties in different cropping systems are responsible for the performance of crops rotation, especially that of CZ11-94-5C-millet. In biennial rotation (cowpea-millet), the best millet grain yields (2 100 kg and 2 000 kg ha−1) were observed after two previous cowpea with
The precipitation regime (year factor) also influenced grains and above-ground dry biomass yields, even though the annual rainfalls were equivalent (654 and 663 mm, resp.). This was explained by the frequency and the ten-day rain quantities which were different during the two millet cropping years (2008 and 2009, Figure
Results of this study showed the performance of cowpea CZ11-94-5C variety nodulation and its contribution to the improvement of the performance of the subsequent millet yield. The tested cowpea varieties and cropping systems did not have a significant influence on mycorrhizal colonization of millet and cowpea roots.
This research was supported by Syngenta Foundation for Sustainable Agriculture. The authors would like to thank Dr. Oumar NIANGADO, representing this Foundation in West Africa. Acknowledgment is also due to Mr. Oumar TOGOLA and Cheick A. KEITA for their assistance in field work; Drs. Drissa DIALLO, Sidy B. COULIBALY, and Minamba BAGAYOKO for reviewing the paper.