Productivity and Land Use Efficiency of Maize-Soybean Intercropping Under Different Tillage Practices at Teppi Southwestern Ethiopia

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Productivity and Land Use Efficiency of Maize-Soybean Intercropping Under Different Tillage Practices at Teppi Southwestern Ethiopia

Behailu Mekonnen

Ethiopian Institute of Agricultural Research (EIAR)

Teppi Agricultural Research Center (TARC), P.O. Box 34, Teppi Ethiopia

Fax: +251475560087, Email: [email protected]

Submitted 14 June 2023 / Accepted 18 July 2023

Abstract

A two-year field experiment was conducted at Teppi Agricultural Research Center during the main cropping season (under rain-fed conditions) from April 2021 to January 2023. The objective was to determine the optimum intercropping combinations and appropriate tillage practices that enhance land use efficiency, yield and economic advantages of maize and soybean intercropping systems. The experiment was laid out using a split-plot design with three replications. The main plot treatments consisted of two tillage practices (zero tillage and conventional tillage), while the sub-plot treatments contained five intercrop combinations of maize and soybean (1:0, 0:1, 1:1, 2:1, and 1:2). Combined data analysis revealed significant (p<0.05) effects of the main effect of maize-soybean intercropping on yield attributes of the component crops and competition indices. However, the main effect of tillage practices and their interaction with intercropping had a non-significant (p>0.05) effect on the yield attributes of the component crops and competition indices. In terms of yield and economic advantage, the intercrop combination of 2:1 maize and soybean recorded the highest total land equivalent ratio value (1.17), area time equivalent ratio (1.16), and monetary advantage index (17,224 ETB ha- 1). Therefore, the findings suggest enhanced resource use efficiency in maize-soybean intercropping, resulting in higher yield and monetary advantage compared to sole cropping. In conclusion, the 2:1 maize and soybean intercrop combination is recommended as the best combination for improved land use efficiency, yield, and economic advantage compared to other combinations.

Keywords: Intercropping, Land use efficiency, Maize, Soybean, Tillage, Yield advantage.

INTRODUCTION

The agricultural systems in Ethiopia exhibit a significant level of fragmentation and are primarily focused on subsistence farming. These systems have limited reliance on advanced technologies and inputs. However, given their current state, these fragmented and subsistence-oriented farming practices are unable to feed the nation's expanding population (Mekuria, 2018; Yigezu, 2021; Zerssa et al., 2021). The traditional agricultural methods in Ethiopia have traditionally

involved multiple cropping, which includes cultivating various species of cereals and legume crops in rotation or mixed patterns (Baye, 2017; Michler and Josephson, 2017). In the southwestern region, in particular, small-scale farmers have long practiced multiple cropping as a means to meet their nutritional requirements and mitigate the risks posed by varying.

Previous studies have indicated that combining maize and soybean through intercropping can lead to increased maize grain yield without significant

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reductions in soybean yield (Dapaah et al., 2003). The presence of soybean crops can enhance the availability of soil nitrogen through biological fixation, which benefits the growth of maize plants (Jensen et al., 2020). However, it should be noted that the improved yield in maize cannot be solely attributed to enhanced nitrogen nutrition; other unidentified factors may also play a role (Connolly et al., 2001).

Factors such as population density and spacing between plants may contribute to the observed yield improvements in maize when grown in an intercropping system. Simultaneous planting of both crops can give rise to competition or facilitation among the plants, both within and between species. Studies have found that competition between maize and soybean mixtures significantly impacts yield compared to sole cropping (Dhima et al., 2007; Yilmaz et al., 2008). It has been observed that deviating from the optimal cropping ratio can result in competition for growth resources, above and below ground, between maize and soybean plants, ultimately diminishing the yield and quality of both crops when compared to sole cropping.

Hence, it is crucial to establish an optimal cropping ratio to manage interspecific competition among maize and soybean plants, thus maximizing the overall yield and economic benefits of the system (Feng et al., 2021)

The impact of tillage practices on crop productivity through soil health is a significant factor. However, excessive tillage in conventional farming has led to environmental and soil degradation (Parihar et al., 2016), which negatively affects crop yields and soil characteristics (Das et al., 2013).

Conservation agriculture has gained attention as an alternative to conventional tillage systems, as it offers the potential to improve soil health and sustain crop output over time. It has been highlighted that conservation agriculture reduces agricultural inputs and labor requirements, particularly for

resource-limited farmers (Kirkegaard et al., 2014). Consequently, it lowers production costs and increases net returns. Previous studies have primarily focused on mono-cropping within conservation agriculture rather than intercropping systems (Falong et al., 2015). Nonetheless, some research has acknowledged the benefits of legume-based intercropping and conservation tillage on soil fertility, the environment, and ecosystem health (Ghosh et al., 2007; Govaerts et al., 2009). Thus, implementing this approach in maize-based systems could be crucial for restoring soil fertility and ensuring sustainable crop productivity. Despite the fact that little research has been done on the benefits of maize-soybean intercropping in the country, there is still a dearth of knowledge on the ideal cropping ratio under various tillage techniques.

Therefore, integrating the maize- soybean intercropping system with tillage practice holds the potential to offer cropping alternatives for smallholder farmers, leading to increased yields and economic benefits. With this objective in mind, our study aimed to determine the optimal cropping ratio under various tillage practices to enhance the productivity, economic profitability, and land use efficiency of maize and soybean intercropping in Teppi, southwest Ethiopia.

MATERIALS AND METHODS Description of the study sites

The study was conducted at Teppi Agricultural Research Center (TARC) during the main cropping season (under rain-fed conditions), from April 2021 to January 2023. The center is in the Southwestern Ethiopian Peoples Regional State, Sheka administrative zone, at Teppi town, located about 611 km from Addis Ababa, the capital city of Ethiopia. It is located at 7°10' N latitude and 35°25' E longitude. The altitude of the site is 1,200 meters above sea level

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Table 1. Monthly minimum and maximum temperature (^oC) of the study area during 2021 and 2022 cropping season

Months

2021 Cropping Season

2022 Cropping Season Min.

(^oC)

Max.

(^oC)

Min.

(^oC)

Max.

(^oC) Jan. 18.3 29.3 19.6 32.8 Feb. 18.2 31.3 20.2 34.1

Mar. 19.9 31 21.1 32.6

Apr. 20.6 28.3 20.2 28 May 20.7 29.5 17.5 25.6 Jun. 20.4 27.1 16.4 24

July 19.9 31 17.4 22.5

Aug. 20.3 28.4 17.2 22.4 Sep. 21.1 27.8 17.3 21.3 Oct. 20.7 30.6 16.5 23.6

Nov. 20.3 33 15.9 28.6

Dec. 19.8 32 16.5 29.1

Figure 1. Monthly rainfall (mm) of the study area (2021 and 2022)

and is characterized by a hot, humid climate (Girma et al., 2008). The average minimum and maximum temperatures of 2021 and 2022 are 20.01 and 29.9 ^oC, 17.98 and 27.05 ^oC, respectively (Table 1). The total annual rainfall in the years 2021 and 2022 was approximately 1410.1 and 1476.17 mm, respectively (Figure 1). The soil type is classified as Nitisol, which is dominated by a loam texture and a pH range of 5.6 to 6.0 (Abayneh and Ashenafi, 2005).

Experimental design, treatments and procedures

The experiment employed a split- plot design with three replications. The main plot treatments consisted of two tillage practices: zero tillage and conventional tillage. The sub-plot treatments involved different

combinations of maize-soybean intercropping. These intercropping treatments comprised five ratios of crop combinations: 1:0, 1:1, 2:1, 1:2, and 0:1, following a replacement design. All treatments were implemented within subplots measuring 3m by 4m (12 m²).

The main plots were spaced 2m apart, while the subplots were spaced 1m apart. For the conventional tillage treatment, the field was plowed three times and thoroughly prepared before planting. In contrast, the conservation tillage treatment involved spraying a non-selective (glyphosate) herbicide on the field one month prior to sowing both crops to control weeds and prepare the area for sowing. The planting dates for the component crops were April 2 and 6 in the 2021 and 2022 cropping seasons, respectively. The study utilized widely adopted maize and soybean varieties: BH-540 and AFIGAT, respectively

During the planting process, specific row spacings were maintained for different planting configurations and crops. Sole-stand plots of maize were planted with a row spacing of 75cm, while soybean plots had a row spacing of 60cm. In an intercropping system with a 1:1 ratio of maize to soybean, the row spacing between maize plants was 75cm, and between maize and soybean plants, it was 37.5cm. Similarly, in a 2:1 ratio of maize to soybean intercropping, the row spacing between maize rows remained 75cm, but the spacing between maize and soybean rows was reduced to 37.5cm. For a 1:2 ratio of maize to soybean, the row spacing between soybean rows was maintained at 60cm, while the spacing between maize and soybean rows was 37.5cm.

Additionally, intra-row spacing was maintained at 25cm for maize and 5cm for soybean. For maize planting, two seeds were initially planted per hill and later thinned down to one plant per hill after the seedlings were well established. The recommended rates of N (nitrogen) and P (phosphorus) fertilizers were applied uniformly across

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all plots. The full dose of phosphorus was applied as a basal application during sowing. The nitrogen fertilizer was divided into two equal splits, with half applied during sowing as basal fertilizer and the remaining half applied at the knee-height seedling stage as side dressing (Adugna et al., 2005). All other agronomic practices were uniformly applied to all experimental plots. At the time of harvest, the crops were manually harvested when they reached physiological maturity, and data measurements were taken from the middle rows of the plots.

Data collection

Data regarding the growth and yield characteristics of the component crops were collected by observing plants cultivated in the central rows.

The grain yield of each crop was assessed and converted into kilograms per hectare (kg ha^-1). To evaluate the agricultural benefits of intercropping, a method described by Willey (1985) was employed. This method involved determining the land equivalent ratio (LER), which measures the efficiency of intercropping in utilizing environmental resources when compared to sole cropping. The LER values were computed using the following formula;

LER = (LERM + LERS), where LERM = YIM/YM and LERS = YIS/YS

Where YM and YS are the yields of maize and soybean as sole while YIM and YIS are the yields of maize and soybean as intercrops, respectively.

The area time equivalent ratio (ATER) is more appropriate for comparing sole cropping and intercropping in this experiment due to the varying growth periods of the component crops. Since maize and soybean have different life cycles, with maize occupying the land for an average of 145 days and soybeans for 120 days, ATER provides a suitable means of comparison. The calculation of the area-time equivalent ratio follows the formula presented in reference (Hiebsch and McCollum, 1987):

ATER = ((Lm*Tm) + (Ls*Ts))/T

Where Lm and Ls are relative yields of partial LER’s for maize and soybean component crops, while Tm and Tlare durations (days) for maize and soybean crops, T is the duration (days) of the whole intercrop system.

The Monetary Advantage Index (MAI) stands out among other competition indices as it specifically measures the economic benefits of an intercropping system. The MAI was calculated as described by Ghosh (2004) as follows:

Monetary Advantage Index (MAI)

= ((value of combined intercrops) x (LER-1)) / LER

Statistical Analysis

The data collected in this study was subjected to a comprehensive statistical analysis. Two-way analyses of variance (ANOVA) were performed using SAS version 9.2 statistical software, ensuring that all the assumptions for ANOVA were satisfied by the data sets.

To identify significant variations among treatment means, the least significant differences (LSD) at the 5% probability level were used.

RESULTS AND DISCUSSIONS Growth attributes of maize

The main effect of intercropping maize and soybean had a significant (p<0.05) influence on the leaf and ear numbers of maize. However, the interaction effect of tillage practices and intercropping did not show a significant impact (p>0.05) on the growth attributes of maize. Sole-cropped maize exhibited the highest number of leaves (12.72 plant^-1) and ears (47355.56 ha^-1) compared to maize-soybean intercropping. Nevertheless, there was no statistically significant difference (p>0.05) in leaf count per plant between sole-cropped maize and the 2:1 maize- soybean ratio. Conversely, the lowest number of leaves (11.88 plant^-1) and ears (25300 ha^-1) were observed in the 1:2 maize-soybean ratios (Table 1)

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The increased number of ears and leaves in sole maize cropping can be attributed to the normal planting density of maize, which eliminates interspecific competition for growth resources. This result agrees with the findings of Paudel et al. (2015) and Wondimu et al. (2016), who reported that the ear number per plant harvested from solely cropped maize was superior to the ear number per plant from intercropped maize with soybean.

Conversely, the decrease in leaf and ear count in the 1:2 maize-soybean ratios might be attributed to intensified interspecific competition with soybean for growth resources, leading to reduced leaf number and leaf area available for photosynthesis, consequently affecting the number of ears per plant. In conformity with this, Teshome et al. (2015) and Negasa et al. (2021) found more ears per plant as the maize population density per unit area increased than the associated soybean population density. Similar results have also been reported by Mbah et al. (2007) and Wondimu et al.

(2016) for maize-soybean intercropping and by Usman et al. (2018) for maize- cowpea intercropping.

Yield attributes of maize

The maize and soybean intercropping had a significant effect (p<0.05) on different yield and yield related attributes such as thousand seed weight, grain yield, aboveground biomass yield, and harvest index of maize. However, the main effect of tillage practices and their interaction with maize-soybean intercropping did not have a significant effect (p>0.05) on the yield attributes of maize (Table 2).

The maximum thousand seed weight (345.72 g), grain yield (4398.6 kg ha^-1) and aboveground biomass yield (10112.4 kg ha^-1) of maize were obtained from sole stands as compared to maize-soybean intercropping.

Similarly, the highest harvest index (0.434) was recorded from the same plot of treatment, but the difference was not statistically significant (p>0.05) when compared to the 1:1 and 1:2 maize-soybean ratios (Table 2).

Whereas, the lowest thousand seed weight (265.83 g), grain yield (2767.4 kg ha^-1), aboveground biomass yield (6727.8 kg ha-1), and harvest index (0.411) were recorded from the 1:2 maize-soybean ratio (Table 2).

Table 2. Effects of tillage practice and soybean intercropping on the growth attributes of maize (mean of two seasons, 2021 & 2022)

Plant Height

(cm) Leaf Number Number of Ears (ha^-1)

Length of Ear (cm) Tillage Practices

ZT 213.51 11.84 31322.22 26.42

CT 235.13 12.40 37511.11 27.03

LSD (0.05) ns ns ns ns

CV (%) 8.16 2.64 6.03 14.19

Intercropping Ratios

Sole M 233.21 12.63^a 47355.56^a 28.03

1M:1S 226.30 12.23^b 29244.44^c 26.20

2M:1S 225.96 12.37^ab 36988.89^b 27.29

1M:2S 225.83 11.88^c 25300.00^d 25.39

LSD (0.05) ns * * ns

TP x IC ns ns ns ns

CV (%) 4.30 2.41 10.53 11.94

Means followed by the same letter(s) within a column are not significantly different at the 5%

level of the LSD test, * = p<0.05, NS = Non-Significant, ZT = Zero tillage, CT = Conventional tillage, M = Maize, S = Soybean.

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Table 3. Effects of tillage practice and soybean intercropping on yield attributes of maize (mean of two seasons, 2021 and 2022)

Thousand Seed Weight (g)

Grain Yield (kg ha^-1)

Aboveground dry Biomass Yield

(kg ha-1)

Harvest Index Tillage Practices

ZT 286.23 3514.50 8299.10 0.42

CT 319.01 3672.10 8512.60 0.43

CV (%) 9.50 25.81 23.30 2.52

Sole M 345.72â 4398.60â 10112.40â 0.43â

1M:1S 295.71^b 3262.50^c 7675.00^c 0.42^a

2M:1S 303.23^b 3944.60^b 9108.20^b 0.43^a

1M:2S 265.83^c 2767.40^d 6727.80^d 0.41^b

LSD (0.05) * * * *

TP x IC ns ns ns ns

CV (%) 4.45 8.18 8.16 1.71

Means within a column followed by the same letter are not significantly different at the 5% level of the LSD test, * = p<0.05, NS = Non-Significant, ZT = Zero tillage, CT = Conventional tillage, M = Maize, S = Soybean.

The absence of inter-specific competition in solely grown maize may enhance the vegetative growth of the plant. This, in turn, leads to better starch accumulation or grain filling, resulting in larger and heavier individual kernels or grains. These findings align with the results reported by Enatalem et al.

(2021) and Negera et al. (2023), who observed that the weight of one thousand seeds in sole-cropped maize exceeded the weight of one thousand seeds in maize intercropped with mung bean and faba bean, respectively.

Furthermore, a significant increase in grain and aboveground biomass yield of sole-cropped maize might be attributed to the availability of optimum space and reduced competition for growth resources. This creates favorable conditions for enhanced growth and higher yields in maize. The result can also be associated with the fact that solely grown maize had the highest number of ears per plant and thousand kernel weights due to the absence of inter-specific competition for growth resources such as nutrients, space, moisture, and light. Besides, the result also indicated that the nutrient requirements of maize and soybean in intercropping systems were superior

over the nutrient requirements of the sole stands of the component crops, as reported by Mbah et al. (2007) and Usman et al. (2018). In accordance with this result, Enatalem et al. (2021) reported higher grain and aboveground biomass yields in sole-cropped maize compared to maize intercropped with soybean. Similar findings have also been reported by Paudel et al. (2015), Khonde et al. (2018), Berdjour et al.

(2020) and Negasa et al. (2021) in maize intercropped with soybean and common bean.

On the other hand, the reduced thousand seed weight, grain, and aboveground biomass yield of maize in the 1:2 maize-soybean ratio might be attributed to the lower density of maize per unit area and the strong competition with soybean for growth resources, which in turn affect the growth and yield of individual maize plants. This result was supported by Teshome et al.

(2015), who observed a decline in maize dry matter yield with increasing population density of intercropped soybeans. The harvest index of maize showed a slight decreasing trend as the population density of intercropped soybeans increased, likely due to reduced grain yield caused by strong

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inter-specific competition. Similar findings have also been reported by Berdjour et al. (2020) and Enatalem et al. (2021).

Yield attributes of soybean

The main effect of tillage practices and their interaction with intercropping maize and soybean did not show a significant effect (p>0.05) on the yield attributes of soybean. However, the main effect of intercropping had a significant effect (p<0.05) on the hundred seed weight, grain yield, aboveground biomass yield, and harvest index of soybean (Table 4). The highest grain yield (1519.36 kg ha^-1) and aboveground biomass yield (4676.28 kg ha^-1) were obtained from sole-cropped soybean in comparison to soybean intercropped with maize. This solo stand also gave the highest hundred seed weight (18.58 g) and harvest index value (0.323) compared to maize-soybean intercropping (Table 4). On the other hand, the lowest hundred seed weight (15.22 g), grain yield (404.73 kg ha^-1), aboveground biomass yield (1399.48 kg ha^-1), and harvest index (0.287) of

soybean were recorded in the 2:1 maize-soybean ratio (Table 4).

In sole-cropped soybean, there was a notable increase in various yield parameters compared to intercropped soybean. Specifically, the hundred seed weight, harvest index, grain yield, and aboveground biomass yield demonstrated improvements ranging from 12.2% to 16.9%, 5% to 11.2%, 58.1% to 73.4%, and 55.4% to 70.1%, respectively. These enhancements can be attributed to reduced competition for resources necessary for plant growth and improved photosynthetic assimilation due to better light transmission in the sole-cropped soybean system, resulting in an increased accumulation of dry matter.

Moreover, higher planting density of sole-cropped soybean may also contribute to the higher grain and aboveground biomass yield (Teshome et al., 2015; Liu et al., 2018). Similar research by Paudel et al. (2015), Berdjour et al. (2020) and Negasa et al.

(2021) also reported yield advantages ranging from 39% to 53% for sole- cropped soybean compared to

intercropped soybean.

Table 4. Effects of tillage practice and maize intercropping on yield attributes of soybean (mean of two seasons, 2021 and 2022)

Hundred Seed Weight (g)

Grain Yield (kg ha^-1)

Aboveground Biomass Yield (kg

ha^-1)

Harvest Index Tillage Practices

ZT 16.17 709.71 2302.81 0.30

CT 16.49 805.43 2539.80 0.31

CV (%) 19.51 7.23 5.47 5.82

Sole S 18.58â 1519.36â 4676.28â 0.32â

1M:1S 16.32^ab 544.23^c 1764.70^c 0.31^b

2M:1S 15.22^b 404.73^d 1399.48^d 0.29^c

1M:2S 16.27^ab 635.95^b 2084.76^b 0.31^b

LSD (0.05) * * * *

TP x IC ns ns ns ns

CV (%) 10.54 12.03 9.74 3.36

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On the other hand, the lower yield observed in intercropped soybean might be attributed to strong competition for soil nutrients and moisture between the companion crops, as well as reduced interception of photosynthetically active radiation (PAR) caused by the shading effect of maize on soybean.

Subsequently, the growth of intercropped soybean could be impeded or suppressed, resulting in decreased light use efficiency, growth rate, dry matter accumulation, and harvest index (Gao et al., 2010; Liu et al., 2017).

Similar findings have also been documented by Fan et al. (2017) and Cheriere et al. (2020).

Effect of Tillage and Intercropping on Competition Indices

a. Partial and Total Land Equivalent Ratios (LERs) The productivity of maize and soybean intercropping was evaluated using three indices: land equivalent ratio (LER), area time equivalent ratio (ATER), and monetary advantage index (MAI). The main effect of tillage practices and their interaction with maize-soybean intercropping did not significantly affect (p>0.05) the partial LER of both maize and soybean as well as the total LER. However, the intercropping had a significant effect (p<0.05) on the partial LER of the companion crops and the total LER. The partial LER values for intercropped maize and soybean ranged from 0.64 to 0.90 and 0.27 to 0.42, respectively (Table 4). The highest partial LER values for maize (0.90) and soybean (0.42) were observed in the 2:1 and 1:2 maize-soybean ratios, respectively. On the contrary, the lowest partial LER values for maize (0.64) and soybean (0.27) were found in the 1:2 and 2:1 maize-soybean ratios, respectively (Table 5)

As indicated in Table 4, the partial LER of maize in all intercrop combinations was higher than that of intercropped soybean, which could be

ascribed to the strong competitiveness of maize over soybean for environmental resources, viz., space, light, water, CO2 and soil nutrients.

Additionally, the increased maize yield also contributed to the significance of its partial LER value. On the other hand, the partial LER value for soybean in all intercrop combinations was lower than the minimal value of 0.5, as suggested by Gliessman et al. (2007), demonstrating a disadvantage for soybean in this intercropping system.

This disadvantage may be due to the dominance of maize, which negatively affected soybean productivity. These findings align with previous studies Worku (2014), Bitew et al. (2021) and Raza et al. (2022) that reported higher partial LER values for maize compared to soybean and common bean in intercropping, indicating maize's yield advantage over soybean and common bean

The total LER for all intercropping combinations was greater than 1, showing that the maize-soybean intercropping system was more productive and yield-enhancing than growing the companion crops alone.

This suggests that maize and soybean are compatible and effectively utilize plant growth resources in the intercropping system. The highest and lowest total LER values of 1.17 and 1.06 were recorded in the 2:1 and 1:2 maize- soybean ratios, respectively (Table 4).

Accordingly, a maize-soybean intercropping with a 2:1 ratio demonstrated greater land use efficiency and biological efficiency, making it an optimal composition for the component crops. The increased productivity of maize and its higher partial LER efficiency strongly contributed to the enhanced total LER value of the maize-soybean intercropping system (Wei et al., 2022).

According to the present results, sole cropping required an additional 17% of land area to achieve the same yield as the intercropping system. Similar findings have also been reported by

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Paudel et al. (2015), Wondimu et al.

(2016), Bitew et al. (2021), Rustiana et al. (2021), and Negera et al. (2023), who observed high total LER values in maize-soybean intercropping.

b. Area Time Equivalent Ratio (ATER) and Monetary Advantage Index (MAI)

The agronomic and economic advantages of an intercropping system cannot be fully exploited by relying solely on the land equivalent ratio (LER).

For a better estimation of the yield advantage in the intercropping system, the area-time equivalent ratio (ATER) becomes an important indicator. Unlike the LER, which only considers harvested products and ignores crop duration, the ATER takes into account the desired yield proportion of the component crops, as mentioned in Khonde et al. (2018). Therefore, the ATER offers a more comprehensive evaluation of the LER values, regardless of the cropping time for each intercropped species (Kherif et al., 2021). Additionally, besides land use efficiency and yield advantage, it is crucial to evaluate the economic feasibility of a given intercropping system before recommending it to farmers. In this regard, the monetary advantage index (MAI) was utilized to evaluate the productivity and economic advantages of the maize-soybean intercropping system. As shown in Table 4, the intercropping had a significant (p<0.05) effect on the ATER and MAI indices of the maize-soybean

intercropping. However, the main effect of tillage practices and their interaction with maize-soybean intercropping did not have a significant (p>0.05) influence on these indices (Table 5)

In all combinations of maize- soybean intercropping, the ATER values exceeded 1, indicating a yield advantage for maize-soybean intercropping compared to sole cropping of the companion crops, even when considering the duration of intercropping. This result is attributed to the cumulative effects of daily productivity within the intercropping system. However, the ATER values were relatively lower than the LER values for all intercrop combinations, suggesting that ATER provides a more comparable estimation of resource utilization than LER (Worku, 2014).

Among the intercrop combinations, a 2:1 maize-soybean ratio produced a significantly higher ATER value (1.17), statistically equivalent to the 1:1 maize- soybean ratio. Conversely, the lowest ATER value (1.06) was observed in the 1:2 ratio of maize-soybean intercropping (Table 4). The 2:1 maize-soybean ratio demonstrated a 16% advantage over sole cropping and other intercrop combinations, indicating optimal space and time utilization by this particular intercropping ratio. This result may be attributed to the increased partial LER of maize, given its strong competitive ability and higher yield during the intercropping period.

Table 5. Effects of maize and soybean intercropping on land equivalent ratio (LER), area time equivalent ratio (ATER), monetary advantage index (MAI) (mean of two seasons, 2021 and 2022)

Partial LER of Maize

Partial LER

of Soybean Total LER ATER MAI

(ETB ha^-1)

1M:1S 0.75^b 0.36^b 1.11âb 1.07âb 10101.00âb

2M:1S 0.90â 0.27^c 1.17â 1.16â 17224.00â

1M:2S 0.64^c 0.42^a 1.06^b 1.04^b 4603.00^b

LSD (0.05) * * * * *

CV (%) 4.13 5.04 1.85 1.89 18.58

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These results highlight that intercropping systems can effectively utilize resources and enhance overall production compared to sole cropping, suggesting a 2:1 maize and soybean combination as the optimal ratio for maximizing yield advantage. These results are consistent with those of Choudhary et al. (2014) and Manasa et al. (2020), who, using comparable intercropping ratios, found the greatest ATER values from maize-soybean (45.2%) and maize-groundnut (13%) intercropping, respectively. Similar results have also been documented by Tamer and El-Rahman (2016) and Telkar et al. (2018)

The MAI values were positive for all maize-soybean intercrop combinations, indicating clear benefits in terms of yield and economic gain compared to sole cropping of the individual crops. The result can be attributed to the enhanced utilization of growth resources by the companion crops and the compatibility of maize intercropping with soybean (Negera et al., 2023). Similarly, the highest MAI value (17224 ETB ha^-1) was observed in the 2:1 maize-soybean ratio, while the lowest value (4603 ETB ha^-1) was recorded in the 1:2 maize-soybean ratio (Table 4). These results suggest that the 2:1 maize-soybean ratio provides the greatest economic advantage compared to sole cropping and other intercropping combinations. This can be attributed to higher overall maize yields with relatively less interspecific competition and a higher LER value for this particular combination. On the other hand, the lowest MAI in the 1:2 maize- soybean ratio can be attributed to lower productivity and yields of both maize and soybean, resulting from strong interspecific competition for plant growth resources. The MAI values followed similar trends as the LER and ATER values for maize-soybean intercropping.

The present finding was in line with the previous studies conducted by Khonde et al. (2018), Negasa et al. (2021), Rustiana et al. (2021), and Raza et al.

(2022), who confirmed that maize- soybean intercropping leads to higher MAI compared to sole maize cropping.

Similar results have also been reported by Liang et al. (2017), Bitew et al.

(2021), Enatalem et al. (2021) and Negera et al. (2023).

CONCLUSION

The results of the two-year experiment showed that the yield attributes of the component crops and competition indices were significantly (p<0.05) influenced by the main factor of maize-soybean intercropping. However, the main effect of tillage practice and its interaction with intercropping had a non- significant (p>0.05) effect on the yield attributes of the component crops and competition indices. The highest harvest index, grain yield, and aboveground biomass yield of maize and soybean were obtained in the sole cropping plots, respectively. These same plots also yielded the maximum values for hundred and thousand seed weights of soybean and maize, respectively. Regarding competition indices, the highest partial LERs for maize and soybean were observed in the 2:1 and 1:2 maize- soybean ratios, respectively. However, the highest total LER value for maize- soybean intercropping was recorded in the 2:1 maize and soybean ratio.

Likewise, the highest values of ATER and MAI were also recorded in the same 2:1 ratio of maize-soybean intercropping.

Therefore, the findings of this study suggest that maize-soybean intercropping enhances resource utilization efficiency, leading to higher yields and economic advantages compared to sole cropping. Accordingly, we can conclude that the 2:1 maize and soybean intercrop combination is recommended as the best combination for improved land use efficiency, yield, and economic advantages when compared to other combinations.

However, before making this recommendation, further studies should

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be conducted for more than two growing seasons by incorporating the minimum tillage practices to evaluate their long- term effects on maize and soybean yield, production costs, and the physico- chemical and biological properties of the soil.

Acknowledgement

I would like to thank the Ethiopian Institute of Agricultural Research (EIAR) for the financial support and the Teppi Agricultural Research Center (TARC) for providing the experimental field for this study, as well as Mr. Awoke Endire, Mr.

Abiyot Andargie, and Mr. Adane Teshome, field assistants of the crop and seed research processes, for their unreserved support on fieldwork from land preparation up to data collection.

Finally, my gratitude goes to Dr. Dereje Tulu for his technical support during the paper's write-up.

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