Agronomic Performance and Productivity of Common Bean (Phaseolus vulgaris L.) Varieties in Double Intercropping with Maize (Zea mays L.) in Eastern Ethiopia

MATERIALS AND METHODS

Description of experimental sites: Field experiments on common bean-maize double intercropping were conducted at Alemaya (in 2003 and 2004) and at Hirna (in 2004), experimental stations of Alemaya University, Ethiopia during the Belg and Meher seasons. The Alemaya (9° 26’N, 42° 3’E, 1980 m asl, average temperature 17°C, average annual rainfall 790 mm, fluvisol) is in eastern Hararghe zone while Hirna (9° 15’N, 41° 6’E, 1870 m asl, average temperature 24°C, average annual rainfall 1045 mm, vertisol) is in western Hararghe zone of eastern Ethiopia.

Test varieties: Seven best performing common bean varieties namely; Ayenew, Roba-1, Gofta, MAM-25, A-197, TY3396-12 and Red Wolaytta (local check) were used. The varieties have bush type growth habit; vary in seed color and seed size. Under sole cropping, the varieties vary in their maturity period (78-110 days). A late maturing maize variety Rarre-1 with white kernel and released for highlands of eastern Ethiopia was used as an associate cereal.

Treatments, trial design and management: Field trials were arranged in randomized complete blocks design in three replications. Each common bean variety was sown in double intercropping with maize. Respective double sole crops of the common bean varieties and the maize were included.

The maize variety was sown in mid-April at both locations and years on a plot size of 5.1x3.75 m (19.125 m²) at 0.75 m inter- and 0.3 m intra-row spacings. Simultaneously, the common bean varieties were sown in between the maize rows at 0.11 m intra-row spacing. The bean-maize intercropping consisted of five rows of maize at rate of 44444 plants ha^-1 (100% of sole maize population) and four rows of bean at rate of 125000 plant ha^-1 (50% of sole bean population) as recommended for the sites (Tamado and Eshetu, 2000). Sole bean was sown at 0.4 m inter-row and 0.1 m intra-row spacing.

In Meher, the respective common bean varieties were sown on the same plot in July immediately after the harvest of the Belg sown bean in both sole and intercropping. Old and dead lower leaves (3-5) of maize were defoliated during the Meher common bean sowing to reduce the shading effect of maize on the bean. The central three rows of maize and four rows of common bean, in both sole and intercropping, were harvested in both seasons.

At time of maize sowing in Belg, all plots received a basal application of diammonium phosphate (DAP, 18% N, 20% P) at the rate of 100 kg ha^-1. At knee high growth stage of maize, N in the form of urea (46% N) was applied at the rate of 50 kg ha^-1 to all plots except the sole common bean plots assuming the common bean would benefit from self-fixed N. Stalk borer (lepidopterous species) incidence on maize was managed by the application of cypermethrin 1% granules once at knee high (50-75 cm height). Hand weeding and frequent hoeing were done.

Belg sown common bean was harvested in mid July at Alemaya and late July at Hirna while Meher sown common bean was harvested in mid November at both locations. Maize was harvested in mid October at Alemaya and early November at Hirna. The maize grain yield was adjusted to 12.5% moisture level and that of common bean to 10%.

Data collection on common bean: For common bean varieties Leaf Area Index (LAI), number of nodules per plant, days to maturity (DM), number of pods per plant, number of seed per pod, 100 seed weight and seed yield were recorded. LAI was calculated as the ratio of total leaf area to ground area occupied by the plant. In determining LAI, all leaves on five randomly selected plants were detached at 50% flowering and their areas were determined using CID-202 leaf area meter (CID, Inc., USA). Ground area per plant was 400 cm² for sole bean and 800 cm² for intercropped bean.

Number of nodules and pods per plant were recorded from a count of 10 randomly sampled plants per plot at flowering and at harvest, respectively. Number of seeds per pod was recorded from 10 randomly sampled pods per plot at harvest. Hundred-seed weight was determined from randomly taken seeds at harvest by adjusting to 10% moisture content.

Data collection on maize: Maize height was measured from five randomly sampled plants per plot from ground level to terminal stem at tasseling. The leaf area was determined as leaf length (L) x maximum leaf width (W) x 0.733 as described by McKee (1964). Then LAI was calculated as the ratio of total leaf area (cm²) of the plant to the ground area (2250 cm²). Thousand Kernel Weight (TKW) was determined after weighing 1000 kernels at 12.5% moisture content. The seeds were counted using electronic seed counter from a sample of threshed seeds from each plot after harvest. Harvest index was calculated as the ratio of grain yield to above ground dry biomass.

Productivity and monetary value of the system: Land Equivalent Ratio (LER), the relative land area required as sole crop to produce the same yield as an intercrop, was used to assess the productivity of the double intercropping to that of sole cropping using the formula described by Willey (1979). Land equivalent ratio

where n is the number of crop species, YiI is the yield of ith species in intercropping and Yim is the yield of ith species in sole cropping. The Meher sole bean yield was considered as a basis for comparison due to the fact that bean is normally grown in Meher season in eastern Ethiopia and the main research question was to compare the productivity of double intercropping of bean with the standard farmers’ practice.

Gross Monetary Value (GMV) was calculated from the yield of maize and bean by multiplying yields of the component crops by their respective market price. During December 2004, the prices for maize and common bean were 1.3 and 1.5 Ethiopian Birr (ETB) per kg, respectively at Harar grain market (1 ETB ≈ 0.12 USD in December 2004).

Data analysis: Analysis of variance (ANOVA) was performed using STATISTICA computer software (StatSoft, 1999) for all data collected in different seasons and locations separately as the seasons and locations are quite different. Least Significance Difference (LSD) test at 5% probability level was used for mean comparison when the ANOVA showed significant difference.

RESULTS

Days to maturity, LAI and nodulation of common bean: Days to maturity (DM) was not significantly affected by cropping system. However, it varied significantly (p<0.05) among varieties in intercropping in Belg at Alemaya and in Meher at Hirna (Table 1). Bean variety MAM-25 matured at the earliest (80 days in Belg at Alemaya and 89 days in Meher at Hirna) while the variety TY3396-12 matured late at both sites and seasons. On average, the varieties matured 15 days earlier in Belg compared with the Meher season at Hirna. However, it was not possible to determine the days to maturity of bean at Alemaya in 2004 due to frost occurrence towards maturity of bean.

The varieties did not show significant differences in their LAI in both locations and seasons except during Meher season at Alemaya where the bean variety TY3396-12 gave the highest LAI of 1.56 in intercropping (Table 1). Sole cropped bean showed significantly (p<0.05) higher LAI than intercropped bean during Meher season both at Alemaya and Hirna in 2004.

Mean number of nodules counted in Belg season were lower than that of the Meher. Although nodulation was not significantly affected by cropping system in seasons and locations, higher number of nodules were counted from sole cropped bean than intercropped bean. The varieties were also not significantly different in their number of nodules when grown in intercropping except in Meher season at Alemaya in 2004. Bean variety TY3396-12 produced the highest number of nodules (78.3) per plant in Meher at Hirna.

Yield and yield components of common bean: Common bean seed yield (kg ha^-1) significantly (p<0.05) varied among varieties in Belg and between sole and intercropped bean in both seasons in 2003 at Alemaya (Table 2). The yield of the varieties under the intercropping ranged from 318.0 kg ha^-1 for Gofta to 581.3 kg ha^-1 for Red Wolaytta in Belg season. In contrast, Meher season and total yields were not significantly different among the varieties. However, sole cropped bean gave significantly higher Belg, Meher and total yields (Table 2). Number of pods plant^-1 and number of seed pod^-1 were not significantly different among the varieties and between cropping systems in both seasons.

In 2004, Belg, Meher and total yields at Alemaya as well as Belg season yield at Hirna were significantly different among the varieties grown in intercropping with maize (Table 3). However, the performance of the varieties over seasons and locations was not consistent. For instance, variety A-197 yielded the highest (996 kg ha^-1) in Belg but ranked 6th in Meher season at Alemaya.

Table 1:	Days to maturity, LAI and number of nodules per plant of common bean varieties grown in intercropping with maize (M) and in sole crop during Belg and Meher seasons of 2004 at Alemaya and Hirna
NR = Not Recorded

Table 2:	Number of pods per plant, number of seeds per pod and seed yield of common bean varieties grown in intercropping with maize (M) and in sole crop during Belg and Meher seasons of 2003 at Alemaya

Variety Gofta showed relatively higher yield performance both in Belg and Meher seasons at Hirna. Similarly, variety TY3396-12 showed consistently better performance in the Meher season at both sites. At both locations and seasons, sole cropped bean gave significantly higher yields (Table 3). Likewise, the varieties revealed significant differences in their hundred seed weight showing that seed weight is a varietal character which is less influenced by management practices. In contrast, number of pods plant^-1 was not significantly different among the varieties and between cropping systems except during Meher season at Hirna where variety TY3396-12 produced the highest number of pods per plant (11.6) compared to other varieties.

Maize component: The LAI of the maize variety Rarre-1 grown in association with the common bean varieties during the Belg and Meher seasons at both locations was not significantly different (Table 4). However, sole cropped maize had higher LAI (mean = 4.08) than intercropped maize (mean = 3.41). Similarly, the common bean varieties grown in association had no significant effect on the height of maize in both years and locations (Table 4 and 5).

Table 3:	Number of pods per plant, hundred seed weight and seed yield of common bean varieties grown in intercropping with maize (M) and in sole crop during Belg and Meher seasons of 2004 at Alemaya and Hirna

Table 4:	Leaf area index, days to maturity and plant height of maize (M) grown in intercropping with common bean varieties and in sole crop at Alemaya and Hirna in 2004

The maize matured within 138 to 150 days and it was significantly different at Alemaya in 2004 where sole maize and maize grown in association with early maturing bean variety MAM-25 matured early (138 days).

In 2003, number of maize ears and grain yield (kg ha^-1) were not significantly affected by the associated common bean varieties except the harvest index (HI). The highest HI (0.47) was obtained from maize grown in intercropping with bean variety TY3396-12 and the lowest HI (0.32) was from sole cropped maize (Table 5). In 2004, the associated bean varieties did not have significant effect on thousand kernel weight (TKW) and HI of maize (Table 6). However, the associated bean varieties had a significant effect on maize grain yield at Hirna (Table 6). At both years and locations sole maize gave higher yields than growing in intercropping (Table 5 and 6).

Productivity and monetary values of double intercropping: Productivity of double intercropping was evaluated using total LER as index. In 2003, the total LER among the various intercropping combinations was not significant. However, in 2004 the total LER values were significantly different at both locations (Table 7). In 2003, the total LERs ranged from 1.28 (for Roba-1) to 1.66 (for Red Wolaytta) indicating 28 to 66% relative yield advantage of double intercropping over sole cropping of the component crops, while in 2004 the relative yield advantage ranged from 25 to 53% at Alemaya and from 6 to 46% at Hirna in 2004.

Table 5:	Plant height, number of ears per plant, grain yield and harvest index of maize (M) grown in intercropping with common bean varieties and in sole crop at Alemaya in 2003

Table 6:	Thousand kernel weight, grain yield and harvest index of maize (M) grown in intercropping with common bean varieties and in sole crop at Alemaya and Hirna in 2004

Table 7:	Total land equivalent ratios (LER) and monetary value of maize and common bean grown in intercropping and sole cropping at Alemaya in 2003 and 2004 and at Hirna in 2004
* 1 ETB ≈ 0.12 USD in December 2004

However, the varieties did not show consistency in total LER over locations, seasons and years. For instance, bean variety Red Wolaytta gave the highest LER (1.66) in 2003 at Alemaya, but gave the lowest LER (1.06) at Hirna in 2004. On the other hand, bean varieties Gofta and TY3396-12 gave consistently higher LER while the early maturing bean variety MAM-25 gave lower LER at both locations in 2004.

The monetary values of double intercropping were evaluated by considering the amount of money that can be generated by growing sole common bean, sole maize or double intercropping common bean with maize. In 2003, at Alemaya, double intercropping of bean variety Red Wolaytta with maize gave the highest GMV of 5652.3 ETB ha^-1 followed by sole maize (Table 7). In 2004, at Hirna double intercropping of bean with maize had a significant effect on GMV (Table 7). At both sites double intercropping of common bean variety Gofta with maize gave the highest GMV (6054.8 ETB ha^-1 at Alemaya, 8097.1 ETB ha^-1 at Hirna). On the other hand, the lowest GMV of 4587.9 ETB ha^-1 was recorded when maize was double intercropped with early maturing bean variety MAM-25 at Alemaya. Double cropping of sole bean gave the lowest GMV of 2644.90 ETB ha^-1 at Alemaya in 2003.

DISCUSSION

Maturity, leaf area index and nodulation of bean: The performance of common bean varied between locations, seasons and years. For example, in Belg season, the common bean varieties compared to Meher season, matured earlier, had higher LAI, but produced lower number of nodules. In general, the LAI and number of nodules from intercropped bean were lower than sole cropped bean possibly due to the shading effect from the cereal component. This result is in agreement with the report of Karikari et al. (1999) where they observed higher LAI in sole Bambara groundnut as compared to Bambara groundnut intercropped with pearl millet and maize. Similarly, Tamado and Eshetu (2000) reported significantly lower number of nodules for common bean grown in intercropping with maize and sorghum as compared to sole cropped bean and attributed this to shading by the cereal components. The variation also depends on the amount of seasonal rainfall as seasonal rainfall affects the use of soil moisture by the component crops, days to maturity and transfer of assimilates (Morris and Garrity, 1993). In high rainfall season (Meher) the common bean tends to be more vegetative and hence matures late. The production of nodules could also be affected by the seasonal rain and temperature that may affect the growth and physiology of the rhizobium bacteria. The varieties matured earlier at Hirna than at Alemaya possibly due to the higher mean temperature at the former site (24°C vs 17°C) which might have hastened growth and development. At both locations and seasons, sole cropped bean gave significantly higher yields than intercropped bean possibly due to absence of competition for growth resources from the cereal component and higher population in the sole crops.

Effect on maize component: Growing of common bean in double intercropping with maize had no significant effect on maize LAI, height, number of ears and grain yield as also reported for single intercropping by Davis and Garcia (1987) and Harwood et al. (2000). In contrast, significant yield reductions of maize intercropped with common bean were reported by other workers (Francis et al., 1982; Fininsa, 1997). It appears that the late maturing maize variety Rarre-1 used in these trials is highly competitive under the highlands of Hararghe conditions to withstand the competition effect of double intercropped common bean for resources and root spaces. However, the magnitude of the effect of common bean varieties on the performance of maize differed in double intercropping.

Productivity and monetary values: The productivity of the double intercropping as determined by total LER, in all combinations, was superior compared to sole cropping in resource use efficiency. The relative yield advantage of the double intercropping as indicated by total LER ranged from 6 to 66% as compared to growing of single cropping of the associated crops separately. This implies that double intercropping intensified crop production both in space and time. The total LER revealed that it would require 0.06 to 0.66 more units of land with the farmers’ practice of single cropping of bean and maize to produce comparable yield to double intercropping of common bean with maize. The yield advantages from such intercropping are reported to be due to better utilization of both underground and above ground growth resources such as light, soil moisture, nutrients by the intercrops than sole crops (Willey, 1979; Rao and Willey, 1980; Ofori and Stern, 1987).

Early maturity is one of the characters required for selecting common bean varieties for double intercropping system. However, the early maturing (75 to 89 days) bean variety MAM-25 showed poor compatibility for double intercropping with maize as compared to the late maturing (80 to 96 days) bean variety TY3396-12 due to its low yield. The latter variety has higher total LER and GMVs over locations and years (Table 7). In addition TY3396-12 was reported for its multiple disease resistance against major common bean diseases (Fininsa and Tefera, 2006). In general, the performance of varieties Gofta and TY3396-12 under double intercropping was relatively better compared to other bean varieties evaluated.

Gross Monetary Value (GMV) was calculated by multiplying the respective yields of the component crops by their market prices and then adding the values of the component crops. The highest LER (1.53) and GMV (6054.8 ETB ha^-1) in 2004 at Alemaya was recorded when bean variety Gofta was double intercropped with maize. However, at Hirna in 2004, bean variety TY3396-12 gave the highest LER (1.46), but the highest GMV of 8097.1 ETB ha^-1 was recorded when bean variety Gofta was double intercropped with maize. This shows difference between agronomic and economic advantages from the intercropping system due to the price differences between the component crops and proves the need for economic evaluation of intercrop systems. Tamado and Eshetu (2000) also reported such discrepancy in agronomic and economic advantages in maize, sorghum and bean intercropping study. Sole bean gave the lowest GMV at Alemaya in 2003 and at Hirna in 2004 which also confirms farmers’ justification of growing common bean mainly as an intercrop in eastern Ethiopia (Fininsa and Yuen 2001).

The present study indicated field based empirical evidence that double intercropping of common bean with maize in the highlands of Hararghe, eastern Ethiopia is feasible, productive and increases household income. The system is also known to enhance biodiversity, conserve soil moisture, avert crop failure risks and diversify crop harvest. Common bean-maize intercropping was also reported to reduce incidence and severity of common bean common bacterial blight (caused by Xanthomonas campestris pv. phaseoli) and rust (caused by Uromyces appendiculatus) (Fininsa, 1996; Fininsa and Yuen, 2002) in Hararghe highlands.

Among the bean varieties evaluated for double intercropping with maize, varieties Gofta and TY3396-12 were found to be compatible. As soil moisture has great significance in double cropping system, study related to soil moisture and possibility of early planting of common bean and late planting of maize to reduce the competition of maize component on the bean might be investigated as a planting schedule in double cropping system at both sites.

ACKNOWLEDGMENTS

The study was financially supported by Alemaya University. We thank Wotatu Wolebo and Seife Lemma, Alemaya University for their assistance in data collection.