Agriculture is a fundamental instrument for poverty reduction, food security, and economic growth. Almost 80% of the Ethiopia’s populations living in rural areas were directly or indirectly linked to agriculture for their livelihood  . However, the sector continues to be undermined by land degradation, depletion of soil organic matter, soil erosion, recurrent drought, poor infrastructure in quality and quantity, backward cultural practices and lack of adequate plant- nutrient supply   . In Sub-Saharan countries, like Ethiopia, where the small- scale farming dominates the overall national economy, agricultural production and productivity were still getting very poor.
World population is exponentially growing indicating the need for an attractive strategy for increasing productivity to fulfill their food requirements such as intercropping. Intercropping is a practice of advanced agro technique of cultivating two or more crops in the same space at the same time for decades where the goals of agriculture have been achieved.
Maize (Zea mays L.) is the most important cereal after wheat and rice with regards to cultivated area in the world  . It is one of the major staple crops in Ethiopia, ranking first in yield potential per hectare and fourth in total area coverage  . The area and production in 2012 were 2.05 million ha (17%) and 6 million tons respectively  . It is compatible with many intercropping systems, gives relatively high productivity per unit area, adaptability to major agro ecologies, and ease in traditional dish preparation. It is food security crop in the country where recurrent drought is a common phenomenon  . Maize production requires adequate supply of nutrients, particularly nitrogen, phosphorus and potassium for good growth and high yield.
But the growing of urbanization and salinization due to improper agricultural land management decreased maize production per unit area each year   . In moisture stress areas of Ethiopia, farmers were adopted harvesting from mono cropping systems only once in a year from a shower of rainfall and cultivating multiple crops in order to harvest best survived crop during the season. Such traditional practices were not potential to harvest adequate amount of food for the family with very small land holding. Improving food production at the national level requires best crop production practices such as intercropping. The maize-legume intercropping has become one of the solutions for food security in small holders farming systems  . Intercropping system showed 41% advantages from maize intercropped with common bean and 23% advantage from maize intercropping with mung bean  .
In addition legume-based cropping system showed 20% to 67% yield benefit of intercropping over sole crop and saved 38% more farm land  . However, no substantial research was done on effect of inter cropping of maize + CB − MB in rates of nitrogen fertilizer on maize production around Arba Minch. Thus studies to look for potential legume as alternative nitrogen source under intercropping system through supplementary nitrogen application was required.
Farmers around the study area were practicing cereal legume intercropping with respect to food harvest but not from the knowhow legume contribution to production, and fertilization. However, the integration of legumes and cereals could significantly contribute to food production and through soil fertility improvement  and enhances efficiency of space and resource utilization which was not noted by the farmers.
These practices in some pockets of land at different parts of the regions were not supported with research findings. Knowledge on combined effects of maize + common bean − mung bean under different rate of fertilizer and benefits of legumes under intercropping system was required in the study area. So the aim of this study was to determine theeffect of intercropping of legumes and rates of Nitrogen fertilizer on yield and yield components of Maize (Zea mays L.)
2. Materials and Methods
2.1. Description of Study Area
The study was conducted at Chano Mille Kebele of Arba Minch zuriaWereda, Gamo-Gofa zone from August to mid January during 2015/16 cropping season. The study area is situated at an elevation of 1216 m.a.s.l., and between 5˚42' and 6˚13'N and 37˚19' and 37˚41'E latitude and longitude ranges, respectively  .
2.2. Weather Conditions
The total rainfall during the growing period, (August to mid January 2015/16) was 614.6 mm the average minimum and maximum air temperatures during the cropping season was 17.4˚C and 33.20˚C, respectively  . The mean temperature comparison indicated that the year 2015 was not warmer than the long term average temperature (Figure 1).
2.3. Physicochemical Properties of Soil
A physical and chemical property of soils of the experimental site from a composite soil sample of 0 - 30 cm depth was analyzed and the result is presented in Table 1.
2.4. Experimental Design and Trial Management
The experiment consists three levels of cropping systems (sole maize, maize intercropped with common bean, and maize inter cropped with mung bean after common bean harvested) and five levels of nitrogen fertilizer rates (0, 23, 46, 69, 92 kg∙N∙ha−1). The cropping systems and levels of N fertilizer rates were combined in factorial randomized complete block design with three replications. The
Table 1. Physical and chemical properties of soils or the experimental site.
Figure 1. Cropping season and the long term monthly averages of the main climatic variables of the experimental site. Source: National Meteorology Agency (2015).
combinations of treatments were as follows:
Sole Maize with 0 kg∙N∙ha−1
Sole Maize with 23 kg∙N∙ha−1
Sole Maize with 46 kg∙N∙ha−1
Sole Maize with 69 kg∙N∙ha−1
Sole Maize with 92 kg∙N∙ha−1
Maize + common bean with 0 kg∙N∙ha−1
Maize + common bean with 23 kg∙N∙ha−1
Maize + common bean with 46 kg∙N∙ha−1
Maize + common bean with 69 kg∙N∙ha−1
Maize + common bean with 92 kg∙N∙ha−1
Maize + common bean with mung bean with 0 kg∙N∙ha−1
Maize + common bean with mung bean with 23 kg∙N∙ha−1
Maize + common bean with mung bean with 46 kg∙N∙ha−1
Maize + common bean with mung bean with 69 kg∙N∙ha−1
Maize + common bean with mung bean with 92 kg∙N∙ha−1
2.5. Experimental Material and Sowing
The experiment was conducted with BH-140 maize variety, common bean (variety Hawassadume) and Mung bean (variety shewarobit). The seeds of maize cultivar were planted at inter and intra-row spacing of 75 and 25 cm. The seeds of common bean were intercropped at the same time with maize in between two consecutive maize rows at inter and intra-row spacing of 37.5 and 10 cm. The seeds of mung bean, for treatments 11 to 15, were planted after harvesting common bean. Each plot had a size of 2 × 3 m2 consisting 4 rows for maize, 3 rows for common bean and 3 rows for mung bean. The experimental plots within a block and blocks were spaced at 0.5 m and 1m, respectively. Sole maize was planted within 2 m × 3 m length plot size having inter and intra-row spacing of 75 and 25 cm. Two central rows with net plot size of 2.25 m2 were harvested and used for data collection. Under intercropping condition maize was planted with the same plot size as that of sole maize.
2.6. Fertilizer Application
Recommended phosphorus fertilizer rate of 46 kg P2O5 ha−1 in the form of TSP was applied for both sole and intercropped crops as basal application during sowing for easy establishment of crops. Specified rates of nitrogen in the form of urea at 0, 23 , 46, 69 and 92 kg∙ha−1 was applied once a time to all treatments as side dressing when the maize crop reached knee height.
2.7. Data Collection
2.7.1. Phenological and Growth Parameters of Maize
During the cropping season data of days to 50% emergence, days to tasseling, days to silking, days to maturity (dm), plant height (cm) and dry matter production (kg∙ha−1) were collected.
2.7.2. Yield and Yield Components of Maize
Number of ears per plant, Ear height (cm), Number of kernels per ear, Hundred kernels weight (g), Grain yield (kg∙ha−1) and Harvest index were collected at the time of data collection.
2.7.3. Assessing Yield Advantages
Land equivalent ratio compares the yields from growing two or more crops together with yields from growing the same crops in monocultures  . LER were calculated using the following formula:
where, Yni is the yield of each crop or variety in the intercrop and Ymi is the yield of each crop or variety in the sole crop or monoculture.
Average or maximum sole crop yields at the optimum fertilizer used as standardization factors for all mixture plot yields of maize as described by  .
Gross monetary value (GMV) was calculated as a product of yields of component crops (kg∙ha−1)) multiplied by their respective price of maize, common bean and mung bean. The price was taken from local markets and monetary advantage (MA) was calculated as:
2.8. Economic Analysis
The economic advantage of the cropping systems was evaluated by estimating net benefit, total cost and marginal rate of return according to  . Market price of maize, common bean and mung bean was obtained by assessing of the market at harvest. In addition to this Labors cost used to estimate cost of production.
2.9. Data Analysis
Statistical analysis of variance of the field experimental data of various parameters was carried out using PROC GLM procedure  version 9.2. Fisher’s Least Significant Difference (LSD) test at P < 0.05 was used to separate significant differences between and among the means.
3. Results and Discussion
3.1. Phenology and Growth Analysis of Maize
3.1.1. Days to Tasseling (DTS)
As indicated in Table 2, increasing N fertilizer from 0 to 92 kg∙N∙ha−1 showed increment of days to 80% tasseling from 73.4 to 75.0. The maximum mean days to attain tasseling were recorded at 92 kg∙N∙ha−1. This result was in agreement
Table 2. Days to 50% emergence, days to 80% tasseling and days to 80% silking of maize as affected by intercropping system and rate of nitrogen application during 2015/16 cropping season.
Where SM = Sole maize; M + CB = maize intercrop with common bean; M + CB − MB = maize intercrop with common bean and mung bean; NS = Non-significantly different at 0.05 probability level; Means followed by the same letters were not significantly different at 0.05 level of significance.
with findings by Moges (2015), who indicated that increasing N from 0 to 128 kg∙N∙ha−1 showed consistent increment of days to tasseling  . Rajcan and Tollenaar also reported that high Nitrogen fertilizer delayed to maize tasseling  .
3.1.2. Days to Silking (DSI)
The mean number of days to attain silking was significantly (P < 0.05) affected by the nitrogen rate but effect of cropping systems was not significant (Table 2). The number of days required to attain silking ranged from 79.3 to 81.4. The maximum number days to silking was recorded at nitrogen rate of 92 kg∙ha−1. This finding was in agreement with the findings reported by Kassahun et al. who documented significant influence of nitrogen fertilizer rate and no significant effect of cropping system on days to silking during maize-bean intercropping system and nitrogen fertilizer application study at wolaitasodo  .
3.1.3. Plant Height
The result showed that plant height was significantly (P < 0.05) affected by N fertilizer rate and cropping system is presented in Table 3. The cultivation of maize attained maximum plant height of 242.4 cm and 236.4cm with full dose of nitrogen (92 Kg∙ha−1) N. The minimum (204.3 cm) plant height was recorded
Table 3. Plant height and days to physiological maturity of maize as affected by rate of nitrogen and intercropping system during 2015/16 cropping season.
where SM = sole maize; M + CB = maize intercrop with common bean; M + CB − MB = maize intercrop with common bean and mung bean; NS = Non-significantly different at 0.05 probability level; Means followed by the same letters were not significantly different at 0.05 level of significance.
with no fertilizer (0 kg∙ha−1) applied. The result suggested that plant height was increased with increasing application of nitrogen fertilizer. The present findings was in agreement with the findings by Haseebur et al. who described that cultivation of maize alone with full dose of nitrogen showed maximum (216.5 cm) plant height whereas, minimum height of maize 184.5 cm was recorded from no fertilizer application  . Furthermore, Dawadi et al. also observed that increasing nitrogen level from 120 kg∙ha−1 to 200 kg∙ha−1 increased plant height of maize varieties  .
Effect of plant height was significant due to cropping system (Table 3). Maximum plant height of 231.6 cm was recorded from sole cropped maize (SM) and the minimum plant height of 224.7 cm was recorded in a cropping system of MZ + CB which is on par with MZ + CB − MB. The maximum (220 cm) and minimum (170.5 cm) plant height was also recorded in sole cropping system and intercropping of maize and fababean, respectively reported by  . The result suggested that plant height was associated with population and competition per unit area where less populated plot with minimum competition showed high plant height. The present findings was in agreement with the findings by Farzaneh et al. who observed higher plant height in sole cropped maize while the minimum in maize intercropped with faba bean  . In addition, Thakur et al. described that maximum (220 cm) and minimum (170.5 cm) plant height was recorded insole cropping system and intercropping of maize, respectively  .
The results of regression analysis as depicted at Figure 2 suggested that the change in fertilizer rate from 0 to 92 kg∙ha−1 accounted for 94.6% of total variation in plant height. The variation in cropping system also accounted for about 81.8% of total variation in plant height suggesting the significant contribution of fertilizer and cropping system for plant height.
3.1.4. Days to Physiological Maturity
As indicated in Table 3, the mean number of days required to attain physiological maturity was significantly (P < 0.05) affected due to rate of nitrogen applica-
Figure 2. The relationships between rate of nitrogen fertilizer and cropping system on plant height.
tion. The result showed that maximum (150.3) days to reach maturity was recorded from 92 kg∙N∙ha−1 whereas, the minimum (142.7) days to reach DPM was recorded for the control treatment. This finding was in agreement with a result obtained from a study conducted at Haromaya district by Kidist who observed significant effect of increasing nitrogen fertilizer effect on days to physiological maturity where plants in a control treatment matured early, while plants at the highest N rates matured lately  . The regression analysis result depicted in Figure 3 showed a linear proportional increase to the number of days required to mature with increasing application of nitrogen rate. The result showed that the change in fertilizer rate from 0 to 92 kg∙ha−1 accounted for about 94.3% of total variation in days to maturity which suggested nitrogen fertilizer application extends the maize growth period.
3.2. Yield and Yield Components of Maize
3.2.1. Kernel Number Per Ear
Application of nitrogen fertilizer showed significant (P < 0.05) effect on kernel number per plant is presented in Table 4. Number of kernel per ear of 420.2 was obtained in plots applied with 92 kg∙N∙ha−1 while the lowest kernel number per ear of 307.7 was recorded in plots with 0 fertilizers. This finding was supported
Table 4. Kernel number per ear, number of ear per plant and ear height as affected by rate of nitrogen and intercropping system during 2015/16 cropping season.
Where SM = sole maize; M + CB = maize intercrop with common bean; M + CB − MB = maize intercrop with common bean and mung bean; NS = Non-significantly different at 0.05 probability level; Means followed by the same letters were not significantly different at 0.05 level of significance according to LSD test.
Figure 3. Relationship between rate of nitrogen fertilizer and physiological maturity of maize.
by Lawrence and Dawadi who described Nitrogen fertilizer application showed significant effect on maize kernel number per cob   .
Application of nitrogen showed a linear response to kernel number per ear (Figure 4). The result of regression analysis result showed that the change in fertilizer rate from 0 to 92 kg∙ha−1 accounted for about 93.6% total change in kernel number per ear.
3.2.2. Ear Height per Plant
As presented in Table 4, the ear height due to nitrogen application ranged from 106.2 to 120.4 cm and maximum ear height per plant was recorded when applying 46 kg nitrogen per hectare.
Mean ear height per plant was significantly affected due cropping system. The mean height was ranged from 104.9 cm to 120.8 cm where the maximum ear height was recorded from sole cropped maize which was on par with maize intercropped with common bean (MZ + CB). The result suggested that ear height per plant was affected due to increased population per unit area which increased competition among the component crops. The present findings was in agreement with the findings by Farzaneh et al. who observed high ear height in sole cropped maize while the minimum in maize intercropped with faba bean  .
The relationship between the rate of fertilizer application and cropping system with ear height per plant is depicted in Figure 5. The change in rate of fertilizer (0 to 92 kg∙ha−1) and various cropping system accounted 29.9% and 89.4% of total variation in total ear height per plant.
3.2.3. Grain yield (kg∙ha−1)
Analysis of grain yield as affected by fertilizer application and cropping system is presented in Table 5. The grain yield of maize due to fertilizer application ranged from 3731.3 kg∙ha−1 to 5345.1 kg∙ha−1. The maximum grain yield was attained applying nitrogen at 92 kg∙ha−1. The result suggested that significant contribution of nitrogen for maximum grain yield. This result was in consistent with Kassahun et al. who described that grain yield of 6751.69 kg∙ha−1 was obtained with nitrogen fertilizer applied at 92 kg∙ha−1. Application of nitrogen significantly increased monoculture maize yield by 30% and soybean yield by 13% reported by Zada and Ahmed  .
Significant responses of maize was observed at highest level of nitrogen application was also documented by Habtamu, Rashid et al. and Siame et al.  
Figure 4. Effect of rate of nitrogen fertilizer on kernel number per ear.
Figure 5. The relationships between nitrogen and cropping system with ear height per plant.
Table 5. Yield and yield components of maize as affected by nitrogen fertilizer application and intercropping system during 2015/2016 cropping season.
Yield is adjusted to 12.5% moisture content; SM = sole maize; M + CB = maize intercrop with common bean; M + CB − MB = maize intercrop with common bean and mung bean; NS = Non-significantly different at 0.05 probability level; Means followed by the same letters are not significantly different at 0.05 level of significance.
 . Maximum grain yield of 4843.3 kg∙ha−1 was obtained in maize + common bean cropping system. The amounts of yield obtained under maize +common bean was on par with sole cropped maize yield (4838.2 kg∙ha−1). The result suggested that maize grain yield was reduced with increasing competition of the component crops. The presence result was inconsistent with the findings documented by Kassahun et al. who reported grain yield of 6496.0 kg∙ha−1 was obtained when common bean intercropped with maize. Furthermore, intercropping effect on grain yield of maize was reported by Tolera (2003) and Kmni et al. (1999) when haricot bean intercropped with maize   .
Alemayehu et al. also reported that maize grain yield was 16% more on maize- narrow leaf lupine intercropping relative to sole crop maize studied on Maize- common bean/lupine intercrop productivity and profitability in maize-based cropping system of Northwestern Ethiopia  .
The regression analysis result depicted in Figure 6 showed a linear response increase to the grain yield with increasing application of nitrogen rate and inversely with cropping system. The result showed that the change in fertilizer rate from 0 to 92 kg∙ha−1 and cropping system accounted for about 95.7% and 74.3% of total variation in maize grain yield respectively, which suggested significant contribution of nitrogen fertilizer application in maize grain yield.
3.2.4. Dry Matter (kg∙ha−1)
As presented in Table 5, dry matter production was significantly affected due to nitrogen fertilizer application and cropping system. The maximum (11,081.8 kg∙ha−1) maize dry matter was recorded when applying 92 kg∙ha−1. The result indicated importance of nitrogen in dry matter accumulation. Similar results were reported by Kena, who described that maximum dry matter yield of (16,529 kg∙ha−1) recorded at the highest nitrogen rate  . In addition dry matter yield increased with increasing nitrogen level also documented by Singh et al. (2000)  studies on intercrops and nitrogen application influence growth and yield of winter maize (Zea mays L.) Furthermore, Cassman et al. (2003) reported that 25% to 75% maize dry matter yield increment over the control treatments was noted with N application  .
The maximum dry matter of 11,168.8 kg∙ha−1 was obtained from sole cropped maize. The present finding coincides with the reports documented by Zeljko et al.  . They discribed that soya bean intercropped with maize showed minimum biomass 17.4 t∙ha−1 when compared to above-ground biomass achieved in
Figure 6. The relationships between rate of nitrogen fertilizer and cropping system on grain yield of maize.
mono crops maize (21.2 t∙ha−1) suggesting advantage of sole cropped maize for growth resources in ability of competition.
The result of regression analysis is depicted in Figure 7. The regression line suggested that dry matter production increased simultaneously with application of fertilizer and inversely with cropping system where the change in fertilizer rate from 0 to 92 kg∙ha−1 and cropping system accounted for 82.2% and 95.6% of total variation in dry matter respectively.
3.2.5. Harvest Index (HI)
Harvest index was significantly (P < 0.05) affected by application of nitrogen (Table 5). The maximum harvest index of 32.2% was recorded when applying 92 kg∙N∙ha−1. The result suggested that the need for nitrogen application to maximize production. This finding was in consistent with the result documented by Moges who reported significant and consistent HI increase with increasing application of nitrogen from 0 to 120 kg∙ha−1.
The result of regression analysis is depicted in Figure 8. Suggested that harvest index increased simultaneously with application of fertilizer where the change in fertilizer rate from 0 to 92 kg∙ha−1 accounted for 91.7% of total variation in harvest index.
3.3. Correlation Analysis
Correlation analysis between grain yield and yield components of maize, phenological and growth parameters was worked out and presented in Table 6. The correlation analyses revealed that there was a significant (P < 0.05) correlation
Figure 7. The relationships between rate of nitrogen fertilizer and cropping system on dry matter of maize.
Figure 8. Relationships between rate of nitrogen fertilizer and harvest index.
Table 6. Correlation analysis of growth, yield, phenology and yield component of maize.
Where; DEM = days to emergency; DTS = Days to tasseling; DSI = Days to silking; DMA = Days to maturity; PH = Plant height; DMT = Dry matter; EHPP = Ear height per plant; NEPP = Number of ear per plant; KNNE = Kernel number per ear; GYLD = Grain yield; HSW = Hundred seed weight; HI = Harvest index; NS, *, ** and *** = non-significant and significantly different at 0.05%, 0.01% and 0.001% respectively.
between grain yield and yield components of maize while the association of yield with phenological and growth parameters showed not significant but positive except days to physiological maturity.
Grain yield was significantly and positively correlated with above ground biomass (r = 1.0**), HSW (r = 0.9**) and HI (r = 0.88**) which suggested significant contribution of yield components on grain yield of maize. This finding was similar with a result obtained from a study conducted at Haromaya district by Kidist who observed a positive correlation of grain yield and biomass yield. Significant and positive correlation was also observed between hundred seed weight and above ground dry matter (r = 1.0**) and ear height per plant (r = 0.8**) and negative and non significant correlation with number of kernel per ear (−r = 0.6).
3.3.1. Intercropping Advantages
The productivity advantage of maize + common bean and maize + common bean with mung bean intercropping system was assessed with land equivalent ratio and monetary value of the treatment combination. As shown in Table 7, cropping system showed significant (P < 0.05) effect on partial land equivalent ratio of maize, total LER, gross monetary values and monetary advantage of the component crops.
3.3.2. Partial LER of Maize
The effect of intercropping system was significant for LER when the maximum LER 1.0 was recorded at Maize + Bean cropping system. Maize + Bean cropping system greater than by 20% compared to maize + common bean − mung bean. The result suggested that maize yield advantage decreased with increase in the no of legumes in the cropping system.
3.3.3. Total LER
Total LER was also significantly affected by the cropping system. The maximum (2.2) total LER was recorded from Maize + Common Bean-Mung Bean. Intercropping three cropping species was greater by 40% compared to intercropping of two crop species. This result agreed with the findings by chemeda who indi-
Table 7. Partial land Equivalent Ratio (LER), total LER, Gross Monetary Value (GMV) and Monetary Advantage (MA) of maize as influenced by intercropping with legumes and rates of Nitrogen fertilizer during 2015/16 cropping season.
Where LER = Land equivalent ratio; GMV = Gross monetary value; MA = Monitory advantage; Means followed by the same letters are not significantly different at 0.05 level of significance according to LSD test.
cated 28% total productivity increase of maize-bean intercropping compared to pure stand  .
Similarly, yield advantages of intercropping on maize was in other study conducted at Kombolcha on system productivity of forage legumes intercropped with maize and performance of the component crops  .
3.3.4. Gross Monetary Value (GMV)
Significant effect of fertilizer application and cropping system also noted on gross monetary values (Table 7). GMV of 83,662 birr∙ha−1 was recorded when applying nitrogen at 92 kg∙ha−1. Application of 92 kg∙ha−1 nitrogen fertilizer gave greater GMV by 16,647 birr∙ha−1 compared to no nitrogen application. Intercropping maize + common bean with mung bean gave significantly higher GMV of 87,191.0 Birr∙ha−1. It was greater than by 55,742.9 birr sole maize. This result supported by a study conducted on productivity evaluation of maize -soybean intercropping system under rain fed condition at Bench-Maji Zone by Solomon et al. (2014) who indicated that the GMV of intercrops was higher than sole maize on maize-soybean intercropping  .
3.3.5. Monetary Advantage (MA)
Significant effect of fertilizer application and cropping system also noted on monetary advantages (Table 7). MA of 45,368 birr∙ha−1 was recorded when applying nitrogen at 92 kg∙ha−1. Applying of 92 kg∙ha−1 nitrogen fertilizer was greater than by 16,997 as compared to no nitrogen application. Intercropping maize + common bean with mung bean gave significantly higher MA of 47,068.2 Birr∙ha−1 when compared to MA of 29,072.5 Birr∙ha−1 obtained in maize + common bean cropping system. This result supported by a study conducted on soybean-maize intercropping integrated fertilizer application with various proportions of NP with FYM by Abebe et al. who indicated that significantly increased MA over the unfertilized intercrops  .
3.4. Economic Analysis
Economic analysis of fertilizer application and legumes under maize based cropping system analyzed and presented in Table 8. There was variation in maize fertilizer and legume combination on total variable cost, net return and marginal rate return. Market price of maize (6.50 birr∙kg−1), common bean (12 birr∙kg−1) and mung bean (20.00 birr∙kg−1) was obtained by assessing of the market at harvest. Labors cost also used to estimate cost of production.
3.4.1. Net Return (NR)
As presented in Table 8, the maximum net return of 55,214.0 birr∙ha−1 was obtained when maize intercropped with common bean followed by mung bean at 92 kg∙ha−1 nitrogen application. The net return of sole maize with all level of nitrogen application exhibited low net return. This result suggested that intercropping and application of nitrogen fertilizer increase net returns for maize production. The finding was similar with a result obtained from a study conducted in
Table 8. Economic of maize as influenced by rates of Nitrogen and intercropping system during 2015/2016 cropping season.
SM = Sole maize; M + CM = Maize intercropped with common bean; M + CB − MB = Maize intercropped with common bean and mung bean; TVC = Total variable cost; NB = Net benefit; D = Dominance and MRR = Marginal rate of return.
southern Ethiopia by Walelign (2013) who observed highest net return from sequential intercropping of common bean and mung bean with maize.
3.4.2. Marginal Rate of Return (MRR)
Maximum marginal rate of 1080% was recorded when maize intercropped with common bean followed by mung bean when applying 69 kg∙ha−1 nitrogen showed above the minimum (100%) rate of return needed for adoption by farmers  .
Greater economic returns were reported in cereal?legume intercropping systems   . This result was similar with a finding obtained from a study on total productivity and net returns of different sorghum-legume intercropping system under varying N levels  .
The result of this study showed that days to maturity, teaseling, silking and kernel number were significantly affected by the main effects of nitrogen rate at 92 kg∙ha−1. In addition grain yield, dry mater and plant height were significantly affected by both the main effects of cropping system and rate of nitrogen fertilizer. The maximum grain yield, dry mater and plant height were observed in maize + common bean cropping system and sole maize at 92 kg∙ha−1 Nitrogen rate respectively. The maximum partial LER was recorded when maize intercropped with common bean. Higher (2.2) total LER were recorded in Maize + common bean with mung bean cropping system. Maximum gross Monetary Value (GMV) of 83,662 Birr ha-1 and 87,191.0 Birr∙ha−1 were obtained when applying nitrogen at 92 kg∙N∙ha−1 and maize intercropped with common bean followed by mung bean cropping system respectively. Results of economic analysis showed that maize intercropped common bean followed by mung bean with nitrogen at 92 kg∙N∙ha−1 gave higher total productivity (80568.49 birr) and net return (55,214.01 birr). Whereas, higher marginal rate of return (1080%) was obtained from maize intercropped with common bean followed by mung bean with nitrogen at 69 kg∙ha−1.
I would like to express my deepest gratitude and sincere thanks to Dr. Zenebe Mekonnen and Dr. Dereje Tsegaye for their guidance and constructive comments at all stages of the research work and thesis write up. Next, I would like to thank Arba Minch Agricultural Research Center for their financial and technical supports. I am also forwarding my heartfelt thanks to Arba Minch University Department of Plant Sciences for their technical support.
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