1. Introduction

Faba bean requires a cool season for best development. It is grown as a winter annual in warm temperate and subtropical areas; hardier cultivars in the Mediterranean region tolerate winter temperatures of -10° C without serious injury whereas the hardiest European cultivars can tolerate up to -15°C ^[1]. "It can be grown anywhere and does not winterkill. Tolerates nearly any soil type; grows best on rich loams. Moderate moisture supply is necessary" ^{[2, 14]}. They are considered to be the least drought resistant of legume crops; however, cultivars with high water use efficiency have been developed at ICARDA ^[2]. "Moisture requirement is highest about 9-12 weeks after establishment. Faba bean is more tolerant to acid soil conditions than most legumes. Growing seasons should have little or no excessive heat, optimum temperatures for production range from 18 to 27°C (65-85°F)" ^[2]. Rainfall of 650-1000 mm per annum evenly distributed is ideal ^[3]. The maturity period ranges from 90-220 days depending upon the cultivars and climatic conditions ^[4].

Faba bean is the most important food legume in the Sudan ^{[17, 18]}. It is the main staple food and the main source of protein for millions of people. Its nutritional importance is even greater as many people have limited access to animal food protein. Its consumption increased among the middle and low income strata of the population, being the traditional dish for breakfast and supper. Further demand has, however, increased over time in the whole country to magnitudes that increasing productivity would be essential to satisfy the local needs.

Faba beans are traditionally grown in the fertile (Gureir) soils, those are silty loams deposited in a narrow strip along the banks of the Nile and on isolated islands. Due to the scarcity of fertile soil and the high demand for Faba bean coupled with the ever increasing prices, new land of inferior quality such as 'karu' and 'high terrace' soils are coming up into production.

The main objective of this study is to investigate the effect of five environments on biological yield and harvest index in six faba bean genotypes.

2. Materials and Methods

A field experiment was conducted for three consecutive seasons (2005/06, 2006/07 and 2007/08), at five environments to investigate the effect of these environments on biological yield and harvest index of Faba bean (Vicia faba L.) in Sudan. The environments selected mainly to represent different soil types. In addition, temperature and relative humidity during the growing seasons were also considered. The environments where: Environment 1 (E₁): Al Salama location: an island 17 kilometers from Atbara city, longitude 33° 99` E, latitude 17° 84` N and altitude 348 meters above sea level to represent lower terrace soil (Riverian).

Environment 2 (E₂): Hudeiba Research Station Farm, longitude 33° 92` E, latitude 17° 56` N and altitude 350 meters above sea level to represent middle terrace soil (Karu).

Environment 3 (E₃): Almatara location 1.5 kilometers from Hudieba Research Station, longitude 33° 95` E, latitude 17° 56` N and altitude 351 meters above sea level to represent high terrace soil.

Environment 4 (E₄): Wad Medani location, Gezira Research Station Farm, longitude 33° 29` E, latitude 14° 24` N and altitude 410 meters above sea level to represent the Central clay plain soil.

Environment 5 (E₅): Ed Damer Food Security Scheme location 2.5 kilometers from Almatara location, longitude 33° 97` E, latitude 17° 54` N and altitude 355 meters above sea level to present high terrace soil (this environment was added in the second and third seasons to study another location of the high terrace soil).

The soil physical and chemical properties for all sites were described by Abdalla et al. ^[5]. The monthly mean maximum and minimum temperatures and relative humidity during the experimental period were recorded ^[5].

Sex Faba bean lines were used in this study:

Small-medium seeded (H.72/7/1, Daba.1/1, Z B F.1/1, C.86 and Triple White); and large seeded Turki. The treatments were arranged in Randomized Complete Block Design (RCBD) with three replications in the three seasons. The land was pre-irrigated and then prepared by disc ploughing, harrowing and ridging at 60 cm apart. Spacing between plants was 10 cm in all seasons. The size of the individual plot was 6 x 3.6 meters consisting of six ridges. The two outer ridges on each plot were left as guard while the inner ridges were used for yield determination. Sowing was done manually on the shoulder of the ridges on the first half of November in River Nile locations. While, Wad Medani location it was sown on the first week of December. The lines were planted at a rate of 3 – 4 seeds per hole and then three weeks later were thinned to 2 plants per hole to gain the recommended plant population (33 plants /m²). Weeds were controlled three times by hand. Crops were irrigated at 8 – 10 days intervals.

Characters studied included biological yield (ton/ha) and harvest index (%), determined according to method described by El Naim et al ^[16].

The data were statistically analyzed using IRRSTAT software computer packages.

3. Results and Discussion

In the three seasons, the biological yield was affected by all treatments (Tables 1a-c). Statistical analysis showed that environment, line and their interaction had a highly significant effect on mean biological yield in the three seasons. The overall mean biological yield was relatively higher in the second season (4982 kg/ha) compared to the first and third seasons (3383 and 4036 kg/ha), respectively (Tables 1a-c). Toker ^[15] found that the biological yield of faba bean was the most strongly affected by environmental conditions.

Table 1(a). Effect of environment, line and their interaction on biological yield (kg/ha) of faba bean grown during season 2005/06

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Table 1(b). Effect of environment, line and their interaction on biological yield (kg/ha) of faba bean grown during season 2006/07

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Table 1(c). Effect of environment, line and their interaction on biological yield (kg/ha) of faba bean grown during season 2007/08

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Average over lines, plants grown at E₁ (Al Salama location) produced significantly the highest biological yield (5511, 9902 and 8064 kg/ha) in seasons 1, 2 and 3 respectively, followed by E₂ (Hudeiba), E₄ (Wad Madeni), E₃ (Almatara) and E₅ (Ed Damer) in the three seasons (Tables 1a-c). The variation in biological yield could be attributed to variations in the growing environments. These results agree with the observations of Dantuma and Thompson ^[6] who stated that soil conditions markedly affect total dry matter productivity.

Average over environments, line C.86 had significantly the highest mean biological yield (3812, 5353 and 4271 kg/ha) in the three seasons, respectively (Table 1a-c). However, the lowest mean biological yield was produced by Triple White (2546, 4253 and 3469 kg/ha) in the three seasons respectively (Tables 1 a-c). Similar variations in biological yield were reported by Toynbee-Clarke ^[7] when he compared whole-plant yields in some major and minor beans. Yield of dry matter ranged from 4900 to 8700 kg/ha, and the spring beans had lower yields than winter cultivars.

The results showed positive correlation between biological yield and seed yield (Tables 1a-c). Almost a similar finding was reported by Agung, et al. ^[8] who pointed out that yield was related to biomass accumulation. Also, Loss and Siddique ^[9] found that faba bean can produce impressive biomass and seed yield in a range of dry land Mediterranean-type environments.

The high biological yield observed in E₁ was attributed to the favourable conditions in this location. Interesting supportive evidence is the finding of Dantuma and Thompson ^[6] that, with potentially high levels of total dry-matter productivity; the proportion devoted to seed production is important. It seems, however, that a high allocation of assimilate to reproductive growth is obstructed by highly fertile growing conditions. However, Thompason and Taylor ^[10] compared crops grown under normal conditions with crops with high cultural inputs to ensure, that resources for growth were available in non-limiting amounts. Their results indicated that non-limiting treatment produced higher yield of total dry matter.

Harvest index of Faba bean lines at different environments in the three seasons is presented in Tables 2a-c. Analysis of variance showed that environment, line and their interaction had a highly significant effect on mean harvest index in the three seasons. The overall mean harvest index was significantly higher in the second season compared to the first and third seasons (Tables 2a-c).

Averaging over lines, plants grown at E₁ (Al Salama) and E₂ (Hudeiba) had slightly higher harvest index in the three seasons. However, the lowest mean harvest index was found at E₄ (Wad Madeni) in the first season and at E₃ (Almatara) in the second and third seasons (Tables 2a-c). The results indicated that high harvest index is recorded under good environmental conditions (E₁ and E₂). Contrasting results were reported by Thompson and Taylor ^[10] who said that crops grown at a lower level of inputs always produced a higher harvest index (HI) than plants grown with minimal constraints to growth.

Table 2(a). Effect of environment, line and their interaction on harvest index % of faba bean grown during season 2005/06

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Table 2(b). Effect of l environment, line and their interaction on harvest index % of faba bean grown during season 2006/07

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Table 2(c). Effect of environment, line and their interaction on harvest index % of faba bean grown during season 2007/08

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Irrespective of environments, line C.86 had higher harvest index (32.4, 43.4 and 35.8) in the three seasons, respectively. However, Triple White line had the lowest mean harvest index (21.2, 37.3 and 25.7) in the three seasons respectively. These results showed considerable variations in harvest index among lines. Contrasting results were reported by Agung, et al. ^[8] who stated that harvest index differed little between genotypes. While, Loss and Siddique ^[9] stated that faba bean had consistently high harvest indices (37-62%).

Table 3. Correlation (r) between grain yield of Faba bean lines and biological yield and harvest index measured in each experimental site of the trial, 2005/2008 seasons

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In this study, the moderately good soil and cool temperature seem to have some effect on the high harvest index observed in E₁ and E₂. A contrasting result was reported by Thompson and Taylor ^[10] who showed that high proportion of total dry matter is utilized for seed production. Harvest index was consistently lower from the plants grown at moderately good soil. However, Fasheun and Dennett ^[11] gave examples of apparently good growing conditions leading to high levels of total dry matter, but relatively low yields of seed. Conversely Ishag ^[12] found that limited vegetative growth was associated with high seed yield and high harvest index. Moreover, Keller and Burkhard ^[13] concluded that the harvest index does not significant from location to location.

4. Conclusion

The results indicated that agro-ecological environment plays considerable role in productivity of faba bean crop. The highest biological yield was produced in low terrace soil Riverian land; Al Salama location. However, low biological yields of faba bean were obtained from the high terrace soil in Almatara location. The highest harvest index of faba bean crop were recorded from the middle and lower terrace soil Environments. The highest biological yield and harvest index were obtained by line C.86 in all production environments tested.

The new production environment, heavy clay soil of Wad Madeni location (central Sudan) produced moderate biological yield of faba bean; thus more further research is needed to come up with appropriate cultural practices to increase the yield of faba bean crop.

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