Advances in Crop Science and Technology
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Intercropping advantage; Land equivalent ratio; Monitory advantage index; Maize

Intercropping is one of the commonly used cropping practices in most tropical areas in Africa. It is the growing of two or more crop species simultaneously in the same land during the growing season. Shortage of the farm land due to population pressure forced to explore new ways to intensify production and productivity per unit area of land. The benefit of intercropping over sole cropping in terms of production per unit area is stated by Nasrietal. It is an attractive strategy to increase the productivity and land use efficiency. Cereallegume intercropping is the most commonly used practice by smallholder farmers in developing countries because of its environmental as well as economic advantages. It is also important for better use of resources, improvement of soil fertility, soil conservation and reduction of risks and suppression of weed infestation. However, the advantage of intercropping is obtained when correspondent species1 has differences in crop architecture, maturity time, nutrient use to optimize the use of natural resources and environmental factors when cropped together [1].

Maize and common bean are the major food crops among cereals and pulses in mid and low land areas of Ethiopia. Maize is the most important cereal crop after wheat and rice with regards in production area in the world and fourth after teff, barley and sorghum in Ethiopia. In view of its importance in terms of wide adaptation, total production and productivity, maize has been selected as one of the high priority crops to feed the increasing human population of Ethiopia. On the other hand, common bean is also a major food crop particularly in Southern and Eastern parts of Ethiopia and it is also considered as the main cash crop and protein source for farmers. Most of the research findings of the previous studies proved that the productivity of intercropping over sole cropping [2].

Intercropping has an advantage and often provides higher economic benefit than mono cropping. Intercropping productivity and economic benefit was determined by using different evaluating indices. Land Equivalent Ratio (LER) and Monitory Advantage Index (MAI) are the commonly used indices adopted in intercropping to evaluate intercropping advantages. LER is an indicator to determine the efficiency of intercropping. Its value greater than one indicates greater efficiency of land utilization in intercropping due to greater efficiency of resource utilization in intercropping [3].

Maize and common bean has been considered as the best component crops in intercropping system because of its suitability to the cropping system. In fact, mono-cropping of maize is the common farmer’s practice in the low lands of Gimbo and Guraferda areas. Due to this, the productivity of the crop has been declined substantially. On the other hand, the demand for food is rapidly increasing and the availability of land for agriculture is shrinking due to population pressure and urbanization [4]. Under this situation one of the most important strategies is intensification of crop production and increasing the productivity per unit area of land. Intercropping is an attractive strategy to increase crop productivity and land use efficiency. However, not much is known about the importance of intercropping in terms of land use efficiency and economic benefit. In addition, there is no research activity conducted regarding intercropping of common bean with maize on yield and economic benefits of the cropping system. Therefore, this study was undertaken to determine the appropriate intercropping row ratio of common bean with maize for better productivity and economic benefit [5].

Description of the experimental site

The experiment was conducted for two years in Kaffa and Bench Maji zones. The specific experimental site is Shomiba Sheka in Gimbo district and Otuwa, in Guraferda district [6]. The experimental site was located at 07°24’ N latitude, 36°26’ E longitude and an altitude of 1233 meter above sea level (Shomiba Sheka site) and 06°50’ N latitude, 35°15’ E longitude and an altitude of 1133 meter above sea level.

Experimental materials

Maize variety BH-540 and common bean variety Hawassa dume were used for this study. These varieties were the most adopted and high yielding varieties in the location [7].

Agronomic practices

The experimental field was ploughed, leveled properly. Sowing was done by putting the seeds in rows at the space of 25 cm and 10 cm for maize and common bean, respectively. NPS fertilizer (NPS 19:38:5) was applied at the rate of 100 kg ha^-1 during sowing. Other than the treatment effects weeding, harrowing and fertilizer application were carried out uniformly in all experimental plots [8].

Treatments and experimental design

Inclusion of common bean by constant maize population was used in the study. The treatments consisted of sole maize, sole common bean, 1:1 and 1:2 row ratios of maize-common bean intercropping, respectively. The experiment was arranged in randomized complete block design with four replications. Each experimental plot area consisted of 4.8 m × 5 m length (24 m²) and 16 m² was used as a net plot area. The distance between plots and blocks were 1 m and 1.5 m, respectively. Plants from the internal rows of net plot area were used for data collection and analysis of the parameters under study [9,10].

Data collection

Grain yield (kg/ha): Grain yield of the component crops were measured from the net plot area and expressed as kg ha^-1. The grain yield was adjusted to recommended moisture content of 12.5% for maize and 10% for common bean. Finally, the data was subjected to the statistical analysis [11].

Land equivalent ratio: The total land area required under sole cropping to give the yields obtained in the intercropping. The LER values were computed using the following formula described by Willey, Willey and Osiru [12].

Where,

Y_ab=Yield of maize when intercropped with common bean; Y_ba=Yield of common bean when intercropped with maize; Y_aa=Yield of sole sown maize; Y_bb=Yield of sole sown common bean.

Monetary advantage index: The yield of intercropping and sole cropping system and their economic return in terms of monetary value were evaluated to find out whether maize yield and added common bean yield are profitable or not. The value of combined intercrops in each cropping system was the lower market prices of maize and common bean in Ethiopian Birr per kg at the time of experiment. The lower average price at Gimbo and Guraferda districts after harvest of crops was 5 birr kg^-1 for maize and 6 birr kg^-1 for common bean. The higher the MAI value the more profitable is the cropping system [13].

Where,
P_ab=P_a × Y_ab P_ba=P_b × Y_ba P_a=Price of maize P_b=Price of common bean

Statistical analysis

The collected data were subjected to statistical analysis using PROC GLM procedures in SAS version 9.3. Variations between the treatment means were compared using Least Significant Difference (LSD) at 5% probability level.

Analysis of variance of the combined data showed significant difference (p<0.05) among the treatments for grain yield. The significant difference was also observed between years for grain yield (Table 1). Among years the higher grain yield was recorded in 2017 than 2018 when we see the mean values of individual year data. B This might be due to the variations in weather conditions of both years (Table 1).

Table 1: Mean squares for source of variation of the component crops.

Effect of intercropping on grain yield of the component crops

The statistical analysis of the data from field experiment revealed that there were significant variations between intercropping and sole cropping on grain yield of maize and common bean. The grain yields of the component crops under sole cropping were significantly higher than those under intercropping.

Maize yield

The result obtained from field experiment indicated that intercropping of common bean with maize had significant (P<0.05) effect on grain yield of maize in both locations. The sole cropped maize and 1:1 maize-common bean intercropping was statistically same at Guraferda. The inclusion of one row common bean in between maize row didn’t affect grain yield of maize. This might be due to less competition between the component crops for nutrients. The higher maize grain yield was recorded for sole cropped maize (6545.7 kg ha^-1) and 1:1 maize-common bean intercropping (6353.9 kg ha^-1) at Guraferda.

However, the lower grain yield of 6158.2 kg ha^-1 was obtained from 1:2 maize-common bean intercropping. The performance of maize in producing grain yield at Gimbo was less than that of Guraferda. The higher maize grain yield of 5570.6 kg ha^-1 was produced in monoculture as compared to the intercropping systems at Gimbo location. However, the lower was obtained at 1:2 maizecommon bean rows (4626.5 kg ha^-1), which was not significantly vary from 1:1 maize-common bean intercropping (5015.4 kg ha^-1) (Table 2). The higher grain yield of sole cropping as compared to intercropping was due to the result of competition between the component crops for natural resources. This result is similar with the previous findings. In contrast, Takim reported that the increased maize grain yield when maize intercropped with cow pea. Among the two locations, the higher grain yield of maize was obtained at Guraferda. It had showed 20% of yield advantage when compared to Gimbo site. This indicates the conduciveness of the area for maize production. It might be due to the variations in soil characteristics and environmental conditions of both locations (Table 2).

Table 2: Mean grain yield (kg ha^-1) of maize when intercropped with common bean.

Common bean yield

Intercropping of maize with common bean significantly affect common bean yield (P<0.05). There was significant variation observed between the locations. When we compare the mean grain yield of the two locations, the higher common bean yield was recorded at Gimbo than Guraferda, which gave 29.5% more yield as compared to Guraferda site. It might be due to the conduciveness of weather condition as well as soil characteristics for the growth and development of common bean in the location.

The higher grain yield of 3407.2 kg ha^-1 was produced from sole cropped common bean at Gimbo. The lower grain yield was obtained from 1:2 (2056.9 kg ha^-1) and 1:1 (2107.8 kg ha^-1) maize-common bean intercropping, respectively. At Guraferda, the highest grain yield of 2638.0 kg ha^-1 of common bean was recorded for sole cropped common bean. The lower common bean yield was recorded from the treatments of 1:2 and 1:1 maize-common bean intercropping with the respective grain yield of 1497.2 kg ha^-1 and 1714.1 kg ha^-1. The more grain yield of common bean obtained from sole cropping as compared to intercropping might be due to more number of plant populations per unit area. Similar result was reported earlier by Tamiru (Table 3).

Table 3: Mean grain yield (kg ha^-1) of common bean when intercropped with maize.

Yield advantages of the cropping system

One of the main objectives of intercropping is increasing productivity per unit area. The productivity and benefit of the maize-common bean intercropping were evaluated by using Land Equivalent Ratio (LER) and Monitory Advantage Index (MAI), respectively. Land Equivalent Ratio (LER) is used for estimating advantages or disadvantages of intercropping over sole cropping system. Based on the result, the intercropping treatments had higher LER than monoculture, which indicated the superiority of intercropping over sole cropping. Likewise, the highest economic advantage was also recorded from intercropping as compared to sole cropping in both locations. In terms of productivity and economic benefit per unit area, the highest yield was recorded for Guraferda location. Growing 1:1 maize-common bean intercropping had the highest land use efficiency and economic benefit than growing 1:2 maize-common bean intercropping at both locations. The higher LER of 1.62 and 1.57 was recorded from 1:1 maize-common bean intercropping at Guraferda and Gimbo locations, respectively. The lower was recorded from 1:2 maizecommon bean intercropping at both locations. It indicates that the growing of one row of maize with one rows of common bean gave a 62% and 57% yield advantage than growing maize or common bean independently as sole crop. This result is consistent with the findings of higher LER in intercropping treatments compared to sole cropping is attributed to better utilization of natural resources. In addition, several researchers reported that the higher LER due to intercropping of legumes with maize, sorghum and rice in different locations.

Monitory advantage index was also evaluated to find out whether maize yield and the added common bean yield are profitable or not. The experimental locations were significantly different in production potential. The higher economic benefit was obtained from Guraferda as compared to Gimbo location. Among the treatments the higher monitory advantage index was obtained from 1:1 maize-common bean intercropping. The higher benefit of 15,268.05 (Guraferda) and 13,695.90 ETB ha^-1 (Gimbo) was also obtained from 1:1 maize-common bean intercropping. However, 1:2 maize-common bean intercropping gave 12,899.74 (Guraferda) and 11,505.05 ETB ha^-1 (Gimbo). The results obtained at both locations were clearly indicated the economic advantages of intercropping over sole cropping. Stated that the yield obtained from combination of the two component crops in the intercropping system was better than the sole yield of either of the two crops. The result is in line with the previous reports in grass-legume intercropping systems. Likewise, Bhatnagar and Chaplot were also reported that a 55% increase in productivity for maize-legumes intercrop as compare to sole cropped maize. The agronomic as well as economic importance of intercropping due to maize with common bean intercropping was also stated earlier by Workayehu and workman (Tables 4 and 5).

Table 4: Land Equivalent Ratio (LER) and monitory advantage index for intercropping of common bean with maize at Gimbo.

Table 5: Land Equivalent Ratio (LER) and monitory advantage index for intercropping of common bean with maize at Guraferda.

Sole cropped maize and common bean had significantly higher grain yield than intercropping. Conversely, the higher intercropping advantage and economic benefit was obtained in intercropping as compared to sole cropping. The combined yield advantage in terms of LER and economic benefit (MAI) was higher due to intercropping 1:1 maize-common bean intercropping. Consequently, intercropping of one row of common bean with one row of maize (1:1) gave the higher yield advantages, 62% at Guraferda and 52% at Gimbo location. Likewise, the higher economic benefits of 15,268.05 ETB ha^-1 and 13,695.90 ETB ha^-1 were also recorded when growing 1:1 maizecommon bean intercropping at Guraferda and Gimbo location, respectively. Therefore, on the bases of the research results, growing 1:1 maize-common bean intercropping gave better agronomic as well as economic advantages. So, it could be suitable combination to increase productivity of land per unit area and economic benefit. Thus, it can be suggested to use for production in the study areas.

We are thankful to the Southern Agricultural Research Institute (SARI) and Bonga Agricultural Research Center for providing the research budget. We would like to thank the staff of Bonga agricultural research center, particularly Ashenafi Abriham, Tesfaye Tarekegn, Demeke Lea and Aminat Hassen for their technical support and cooperation during the field work.

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