Biological Benefits of Intercropping Maize (Zea mays L) with Fenugreek, Field Pea and Haricot Bean Under Irrigation in Fogera Plain, South Gonder Zone, Ethiopia

An on-farm experiment was conducted in the dry season of 2012/2013under irrigation at Jigna rural village of Dera District, South Gonder Zone/Ethiopia. The experiment was conducted to assess the biological benefits of intercropping maize with fenugreek, field pea and haricot bean. A field have a total of 7 treatments, namely three intercropping of fenugreek, field pea and haricot bean with maize and their four sole cropping, were laid out in randomized complete block design (RCBD) with three replications. Gross plot size of each treatment was 3m × 2.7m (8.1m 2 ), but net plot size varied up on the crop types. Spacing between adjacent replications and plots was 1.5m and 1.0m, respectively. Fenugreek, field pea and haricot bean as sole crops were planted at inter-row and intra-row spacing of 20cm × 5cm, 20cm × 5cm and 40cm × 10cm, respectively. In both intercropping and sole cropping maize was planted at 75cm× 30cm interand intrarow spacing, while fenugreek, field pea and haricot bean were intercropped in the middle of two maize rows at their recommended intra-spacing. Varieties used for the present study were BH-540 maize hybrid, "Challa” fenugreek, "Burkitu" field pea and "Awash Melkassa" haricot bean. Data of phenological, vegetative growth and, yield related crop parameters were timely collected following their respective standard methods and procedures, and further subjected to analysis of variance (ANOVA) using SAS version 9.2. Whenever the ANOVA result showed significant difference among treatments for a parameter mean separation was further done using Duncan’s New Multiple Range Test (DNMRT). Intercropping didn’t show any significant effect statistically (p<0.05) on phenological, vegetative growth and yield related parameters of the component crops. However, concerning biomass of fenugreek, field pea and haricot bean, the analysis of variance showed that there has significant difference (p≤0.05) between intercropping and sole cropping. On the contrary, intercropped field pea produced higher pod per plant, plant height and seed per pod than that of sole field pea. Intercropped Haricot bean was also produced slightly higher plant height, seed per pod and thousand grain weights than its sole crops. Therefore, in the present study area during dry season under irrigation, maize intercropping with haricot bean and field pea was more advantageous than their respective sole crops.


Introduction
The limited land areas are facing pressure to meet basic demands of human being for food, fiber and oil. Because of rapid human population explosion, the size of cultivable land at household level is gradually decreasing and most farmers own very small plots of land, especially in the developing countries of Asia and Africa. Hence, there is a need for increasing crops production per unit cultivated land using various techniques including multiple cropping. Intercropping for instance is one of the potential strategies of increasing productivity per unit cultivated land for the subsistence farmers who operate with low resources and inputs (Francis, 1986a). Field Pea and Haricot Bean Under Irrigation in Fogera Plain, South Gonder Zone, Ethiopia According to Willey (1991), intercropping is the practice of growing two or more crops simultaneously in the same field. Higher productivity per unit cultivated area and insurance against the vagaries of weather, as well as disease and pests damages are the major reasons for the existence of intercropping (Papendic, 1983). By growing more than one crop at a time in the same field, farmers maximize water use efficiency, maintain soil fertility, and minimize soil erosion, which are the serious drawbacks of mono cropping (Francis, 1986b;Hoshikawa, 1991). Intercropping also hampers germination and growth of weeds (Palaniapan, 1985). In most instances, intercropping offers the advantages of increasing yield, nutritional diversity and net income (Pal et al., 1981;Aleman, 2000). It is an important practice adopted throughout the tropics and subtropics of Africa, India, and South and Central America (Palaniapan, 1985;Pal et al., 1993;Aleman, 2000). Farmers in different parts of the world intercrop different crops according to their preference based on social and biological needs (Andrew and Kassam, 1983;Francis, 1986a;Francis, 1990).
Intercropping as a method of sustainable agriculture is the growing of two or more crops during the same season on the same area so as to utilize common limiting resources better than the species grown separately, and hence it is as an efficient resource use method (Ghosh et al., 2006). Intercropping of cereals with legumes has been popular in humid tropical environments (Tusbo et al., 2005) and rain-fed areas of the world (Ghosh et al., 2004) due to its advantages for yield increment, weed control (Poggio, 2005), insurance against crop failure, low cost of production and high monetary returns to the farmers (Ofori and Stern, 1987), improvement of soil fertility through the addition of nitrogen by biological fixation (Gosh et al., 2006), improving yield stability, socioeconomic and some other merits (Willey, 1979).
Research has been conducted on maize-faba bean intercropping in many parts of the world, especially in the high lands of eastern and southern Africa, and in Mexico (Minale et al., 2001;Mbah et al., 2007). Maize as a third cereal product of the world has been recognized as a common component in most intercropping systems (Adeniyan et al., 2007). Maize is also used as major food source for Ethiopians. Faba bean is a valuable crop for intercropping with maize, while it has several good features such as shade tolerance (Nasrullahzadeh et al., 2007), symbiotically fixing atmospheric nitrogen and thereby adding valuable nitrogen to the soil (Wenxue et al., 2005), and containing high amount of protein among the legumes (Matthews and Hary, 2003). Intercropping of maize (Zea mays L.) with legumes crops is a common feature of crop production in densely populated areas of eastern Africa such as the highlands of Ethiopia including the study area. The intercropping system might be important for intensification of crop production and to increase economical and biological returns to smallholder farmers in the study area who have limited land holdings, on average about 0.6 ha per household (personal opinion).
Growing of maize during dry season with irrigation is expanding year after year in the study area of Fogera Plain.
During the dry season, irrigation in the study area is being practiced two times in a year to grow different crops. The first round is carried out from October to end of February so as to grow mainly onion, potato and tomato, while the second round is undertaken between March and June to produce mainly maize and rice. Especially maize is produced during this period for market sale at its milk to dough stage. As the annual report of Agricultural Office of Dera District the total irrigated area covered in the first round in the years of 2011, 2012 and 2013 was 5833, 8785 and 10026 hectares, respectively. The same report also indicated that in the second round of irrigation in 2011 and 2012 fiscal years 513.5 and 806.5 hectares of land was covered with crops, respectively in the District. In the study area (Fogera Plain), despite of the expansion of maize production during dry season with irrigation mainly as a sole crop, maize production under irrigation has never been intercropped with other crops. Indeed, some farmers in the study area practice maize intercropping with some crops during rainy season. The prominent problems accounted for the low area coverage of intercropping under irrigation during dry season in the country includes lack of proper planting materials and inappropriate agronomic practices as well as no extension working packages prepared for intercropping under irrigation during dry season.
Some years back farmers were practicing crop rotation, fallowing and other sustainable cropping systems. This effort, which helped farmers to maintain their soil fertility, is currently diminished as the increment of the population and the shrinkage of farmers land holding sizes. Now a day, the most dominant farming system or practice is mono-cropping system, which in turn contributes to decrease soil fertility and worsens on the contrary weed, pest and disease infestations. All these ecologically unfriendly practices render to reduce the production and productivity of crops. To averse this situation by using sound cropping system in a given small area of farmers' lands is the issue of sustainability.
In line with this hence, practicing of intercropping during dry season under irrigation would have more advantage to maximize the harvest of solar radiation and increase the high productivity of crops. Also it has an advantage on photosynthesis process than that of rainy season; while high solar radiation favored with clear sky of dry season might be intercepted by intercropping more effectively than sole cropping that might in turn contribute a lot for increasing productivity and diversity of crops per unit irrigated land.
The main Objectives of the present study was therefore to assess biological benefits of maize intercropping with fenugreek, field pea and haricot bean in Fogera plain of Northwest of Ethiopia under irrigation.

Intercropping for Greater Productivity and Risk Avoidance
Intercropping is the planting of more than one crop on the same land at the same time. In terms of land use, growing crops in mixed stands is regarded as more productive than growing them separately (Andrew and Kassam, 1976;Willey, 1979). Mixed cropping is practiced traditionally in many parts of Africa, Asia, and Latin America (Ahmed et al. 1979). Interest in cereal legume intercropping is also developing in some temperate regions with warm climates such as Australia and the United States (Searle et al. 1981;McCollum, 1982;Allen and Obura, 1983). This may be due to some of the established and speculated advantages of intercropping systems such as higher grain yields per unit land area, greater land use efficiency, and improvement of soil fertility through the addition of nitrogen by fixation and excretion from the legume component (Willey, 1979). It seems worthwhile to develop cropping systems that have the capacity to maximize crop yields per unit land area while keeping the fertilizer nitrogen requirement to a minimum. Intercropping of legumes with cereals offers scope for developing energy efficient and sustainable agriculture (Papendick et al., 1976;IAEA, 1980). Risk avoidance is one of the prominent advantages that intercropping offers (Willem, 1990). It is a system to escape or to avoid the vagaries of nature like drought stress and disease and pest attack (Papendic, 1983;Francis, 1986a;Singh, 1990). It minimizes risk in such a way that the reduced performance of one component crop may be compensated by yield from the remaining component (Rao and Willey, 1980;Andrews and Kassam, 1983). Intercropping systems also minimizes risk with respect to water logging and price fluctuations. For instance, Struif (1986) reported that intercropping sorghum with rice alleviated the risk of crop failure in seasons of water logging on vertisols. Njoroge and Kimemia (1995) indicated that as coffee prices fall, intercropping the young trees with vegetables has been suggested as a way of providing farmers with extra income as well as improving their diet.

Resource Use in Intercropping System
One of the advantages of intercropping system is its efficient and complete use of growth resources such as solar energy, soil nutrients, and water (Francis, 1986a;Sivakumar, 1993). Intercrops are most productive when their component crops differ greatly in growth duration so that their maximum requirement for growth resources occur at different times (Fukai and Trenbath, 1993). For high intercrop productivity, plants of the early maturing component should grow with little interference from the late maturing crop. The latter may be affected by the associated crop, but a long time period for further growth after the harvest of the first crop should ensure good recovery and full use of available resources (Francis, 1990;Siva Kumar, 1993;Fukai and Trenbath, 1993).
Intercropping allows effective utilization of growth resources through crop intensification both in space and time dimensions. The conventional ways of intensifying crop production are vertical and horizontal expansions. Intercropping offers two additional dimensions, time and space (Palaniappan, 1985;Francis, 1986a).
The intensification of land and resource use in space dimension is an important aspect of intercropping. For example, enhanced and efficient use of light is possible with two or more species that occupy the same land during a significant part of the growing season and have different pattern of foliage display. Different rooting patterns can explore a greater total soil volume because of the roots being at different depths (Palaniappan, 1985;Francis, 1986a). These differences in foliage display and rooting patterns create the space dimension of intercropping.
Another important feature is a difference in time of maturity and hence in nutrient demand among different species in intercropping which will create the time dimension of the system. The difference in time dimension will lead to efficient utilization of resources by lessening competition among the intercrop components (Papendic, 1983;Palaniappan, 1985;Trenbath, 1986). The ability of intercrops to intensify resource use both in space and time dimension makes greater total use of available growth resources than mono cropping (Francis, 1986a).
Intercropping increased the amount of solar radiation intercepted due to faster canopy cover, which lead to efficient utilization of light resources (Ramakrishna and Ong, 1994). Keating and Carberry (1993) stated that intercropping offers the advantage of efficient interception and utilization of solar radiation than mono cropping. Improved productivity per unit incident radiation could be achieved by the adoption of an intercropping system that either increase the interception of solar radiation and /or had greater radiation use efficiency. Minimizing the proportion of radiation energy reaching the ground is a simple means of promoting efficient utilization of incident solar radiation (Keating and Carberry, 1993;Ramakrishna and Ong, 1994). Advantages from intercropping of short and long duration species is due to enhanced radiation capture over time. Improved utilization of radiation energy resulted in more efficient production of biomass or increased proportion of biomass partitioned to yield. Azam, et al., (1990) observed an increase in total dry weight of sorghum -groundnut intercrop.
Nutrient Use Efficiency (NUE) of the individual crops in an intercrop is mostly lower than their respective sole crops. However, the cumulative NUE of an intercropping system was in most cases higher than either of the sole crops (Chowdhury and Rosario, 1994). They reported that in maize/mung bean intercropping the nutrient absorption by both maize and mung bean was reduced due to intercropping, mung bean being more affected than maize. Similarly, higher land equivalent ratio over unity was due largely to a higher total uptake of nutrients by the component crops in the mixture than the sole crops. Chowdhury and Rosario (1994) also reported greater efficiency of intercrops than that of the sole crops in converting absorbed nutrients to seeds/grains also contributed to the yield advantage. Morris and Garrity (1993b) reported that, on average intercrops took up 43% more phosphorus and 35% more potassium than the sole crops.
The larger and longer duration of functional root systems Field Pea and Haricot Bean Under Irrigation in Fogera Plain, South Gonder Zone, Ethiopia under intercrops than either sole crop were postulated by researchers explaining the greater capture of non mobile nutrients like phosphorus and potassium. Enlarged root systems provided an expanded root surface area to which non-mobile nutrients diffused (Morris and Garrity, 1993b). Intercrops are also found to be more efficient in water use than mono crops. It was indicated that there was variation in total amount of water used and in water use efficiency among different cropping systems. Morris and Garrity (1993a) computed that mono cropped cowpea used 172 mm, mono cropped sorghum 135mm, the intercrops 162 mm, and fallow 121mm of water. Mean water use efficiency by mono cropped cowpea, mono cropped sorghum, and the intercrops was 11.3, 12.4 and 16.5 kg glucose /ha/mm, respectively and hence the intercrops used water more efficiently.

Competition Versus Complementarity in Intercropping
Complementary use of resources by intercrop implies minimizing competition. Use of different resource pools by the component crops represents the most common example of complementarity. The temporal use of irradiance within intercrops of contrasting development and phenology is a prime example illustrating the more efficient use of naturally available resources by intercrops than by each crop (Midmore et al. 1988a).
The spatial uses of soil moisture by crops of contrasting demand, example chilli pepper and soybean or contrasting root extraction zones also illustrate the efficient use of resources between component crops. Other than complementarity in resource use, component crops can complement each other through other mechanisms. For instance, in a chilli pepper/soybean intercropping intercropped chilli had greater leaf water potential due to the wind break effect of the companion crop, soybean. Relay planting of potato in to the shade of maize in warm climate, showed earlier emergence and represented another complementary effect (Midmore et al. 1988a).
Complementary use by component crops of the same resource pool is less common, but exemplified by the mixing of short C3 and tall C4 type plants, which differ in efficiency in use of tropical sun light (Midmore et al. 1988a). Complementary use of resources therefore takes place over space, time or combination of the two. The stage at which complementarity evolves in to competition for resources is amenable to manipulation through choice of agronomic management. Optimal use of natural resources is attainted when mixture are not comprised of highly competitive crops. Evidence suggests that intercrop stability over space and time is likely to be favored by the choice of less aggressive cultivars (Cenpukdee. U and S. Fukai, 1991).
Under adverse conditions, example nitrogen deficiency or drought, growth is reportedly dominated by the aggressive species (Fukai et al. 1990). Previous studies also indicted that low soil nitrogen and phosphorus improved the competitiveness of cowpea and decreased that of the dominant maize (Chang and Shibles, 1985 a, b), resulting in greater complementary in resource use and higher land equivalent ratio (LER). Competitiveness of component crops therefore depends to a large degree on each crops response to the limiting factors.

Plant Density in Intercropping System
In spite of the capacity for greater productivity of mixed cropping, farmers do not often realize its beneficial effects partly because they often plant their crops at sub optimal population densities (Pal et al. 1993). The associated species and temporal differences between the component crops determine the total plant population required to obtain a yield advantage in intercropping. The total density can also be determined depending on the environmental resources and growth habits of the species.
When there was severe drought, intercropping beans with maize resulted in greater stability of production, since any loss of plant density of one crop tended to be compensated by the other crop which is a major factor influencing the decision to intercrop (Willey, 1979). Component populations mainly determine as how much of the final yield is contributed by each component. When the component crop densities are approximately equal, productivity and efficiency of intercropping appears to be determined by the aggressively dominant crop (Willey and Robert, 1976).
The growth and yield of a legume component is often reduced markedly when intercropped with high densities of a cereal component. For instance, Ofori and Stern (1987b) indicated in a maize/ bean intercropping that increasing maize density from 18000 to 55000 plants/ha reduced leaf area index by 24% and seed yield by 70% in the component bean. An experiment on the effect of plant densities of sorghum, spatial arrangement of component crops and fertilizer on growth and yield components of sorghum and bean (Phaseolus vulgaris) also showed significant differences on pod setting, pod retention, pod length, number of branches and nodulation of intercropped bean (Kassu, 1993).
Similarly, intercropping study that involved sorghum and groundnut with different spatial arrangements also showed highly significant differences in dry pod of the associated groundnut due to the effect of spatial arrangements (Gobeze, 1999). Sole cropped groundnut gave better pod yield than intercropped groundnut whereas among the intercrop treatments the highest dry pod yield was obtained from 40% sorghum: 60% groundnut. Days to maturity and plant height of the associated sorghum were not significantly affected by spatial arrangement of sorghum and groundnut. The results of field experiments conducted in Nigeria involving varying densities of sorghum and maize intercropped with soybean indicated that yields of component crops in the intercrop varied significantly with the components population density (Pal et al. 1993).
In a maize/faba bean intercropping Tilahun (2002) reported the highest plant height of maize at 75% maize: 25% faba bean planting density in a 1 maize: 2 faba bean rows of planting arrangement. Slightly higher grain yield per plant was also observed in case of 50% maize: 50% faba bean plant density in a 1 maize: 1 faba bean row arrangement.
Significantly higher leaf area index was also recorded at 100% maize: 75% faba bean in a1 maize: 2 faba bean row arrangement.

Intercropping and Nitrogen Fixation
The overall benefit of growing two crops in a mixture is the net benefit in which the increase in growth of one crop exceeds a small competitive reduction in the growth of the other (Willey, 1979) and this is often seen where a slow growing legume is intercropped with a tall cereal. Competition for soil N between the cereal and legume components of the intercrop often results in the legume deriving a greater proportion of its N from N2 -fixation, as demonstrated with pigeon pea/cereal intercrops (Tobita et al., 1994;Sakala et al., 2001). The extent to which growth and the total amount of N2 fixed by the legume crop decreased in the intercrop depends on the degree of complementarity between the corps. A much-quoted example of the benefits of intercropping legume and cereal is that of pigeon pea intercropped with maize or sorghum (Ong et al., 1996).
The early growth of pigeon pea was very slow so that it affords little competition and yields of the cereal crops were unaffected (Sakala et al., 2001). When intercropped with maize or short duration varieties of sorghum, pigeon pea continuous to grow on residual soil moisture long after the cereal crop has been harvested, and the amount of N2 fixed by pigeon pea was the same when grown in mixture or as sole crops (Sakala et al., 2001). In an experiment conducted on intercropping, it was indicated that nodulation and nitrogen fixation of groundnut were greatly reduced when it was intercropped with maize, sorghum or millet (Nambiar et al., 1983a).
Similarly, growth and nitrogen fixation of soybean were reduced by a tall sorghum intercrop, where as nitrogen fixation per plant was enhanced by a dwarf sorghum (Wahua and Miller, 1978), indicating that the reduction in yield and nitrogen fixation was partly caused by shading. The available evidence indicated that inputs of fixed nitrogen were more likely to benefit subsequent crops. The beneficial effects of the legumes on succeeding crops can often arise due to a variety of other effects such as reduction of disease incidence or by reducing striga damage as well as change in soil fertility (Reddy et al., 1994;Marcellos et al., 1997). For grain legumes to play an important role in the maintenance of soil fertility, they must leave behind more nitrogen from N2fixation than the amount of soil nitrogen that is removed in the crop. The amount of nitrogen added to the cropping system is very variable for all of legume species. The largest net benefits tend to found with groundnut and cowpea as some varieties of these crops have small nitrogen harvest index (Bell et al., 1994).
A study in northern Nigeria indicated that maize grain yield was found to be greater following a groundnut than after cowpea, cotton or sorghum. The yield increase was related to an increased availability of mineral nitrogen in the soil after groundnut. The fact that no such beneficial effect was found after growth of cowpea in the same experiment indicates that residual effects do not always occur. Groundnut and cowpea were found to have roughly equal residual effects on the growth of a subsequent maize crop in northern Ghana, equivalent to the addition to 60 kg fertilizer nitrogen. This was despite the fact that 68 kg N ha-1 was left behind in above ground residues after groundnut and 150 kg Nha-1after cowpea (Dakora et al., 1987). Direct evidence of the benefits from N2-fixation was obtained where yield of sorghum grown after nodulating varieties of chickpea were better than yields after non-nodulating chickpea (Kumar Rao and Rupela, 1998).
In India, pigeon pea was found to give a residual benefit to subsequent maize of 38 to 49 kg N ha-1 (Kumar Rao et al., 1983). The amount of nitrogen in leaves that fall during growth of long duration pigeon pea may be as much as 68-84 kg N ha-1 (Kummar Rao et al., 1996b;Sakala et al., 2001). Over 12 years, yields of sorghum were consistently higher following a sorghum/pigeon pea intercrop than after an oil crop safflower (Carthamnus tinctorius), and the soil nitrogen content had increased significantly where pigeon pea had been grown (Rego and Rao, 2000). Other legumes may also contribute substantial amount of nitrogen during crop growth. For example, about 81 kg N ha-1 were measured in leaf fall from soybean in Australia (Bergersen et al., 1992). Yield of maize grown after soybean on an Alfisol were increased to 4 tone ha-1, compared with only 1.8 tone in continuous maize cropping where all the legumes stover had been removed (Kasasa et al., 1999).
There is little evidence for direct transfer of significant amount of nitrogen between roots of legumes and cereals in mixtures, and this conclusion is supported by measuring natural N abundance in intercrops of pigeon pea and sorghum (Tobita et al., 1994). Although pigeon pea loses large amount of nitrogen in leaves that fall during crop growth, the leaves cause an initial immobilization of soil nitrogen when they decompose and so little of the nitrogen is available for use by the intercropped cereal (Sakala et al., 2000). Although intercrops can produce greater yields, they generally do so by extracting more nutrients from the soil than sole crops (Mason et al., 1986) and may cause more rapid decline in soil fertility. Similarly, intercrops use more water for growth. When rainfall was adequate a cowpea /maize intercrop gave superior crop yields, but competition for moisture in a drought year caused drastic reduction in yields of intercropped maize (Shumba et al., 1990).

Effects of Fertilizer Application in Intercropping System
In cereals-legumes intercropping, the legume component is capable of fixing atmospheric nitrogen under favorable conditions and this is thought to reduce competition for nitrogen (Trenbath, 1976). In the absence of an effective nitrogen fixing system, both the cereal and legume components compete for available soil nitrogen (Ofori and Stern, 1987a). In a maize cowpea intercropping system, Wahua (1983) found that at 105 kg N/ha, component crops exerted competition for nitrogen just before flowering. The competition for nitrogen was severe for cowpea at 40 days after planting and for maize 10 days later. In the same study it was indicated that nitrogen uptake of intercropped maize was reduced by 19% compared to sole maize. Pal and Shehu (2001) reported that the contribution of legumes to the total N uptake of maize in a mixture ranged between 25 to 28 in soybean, 24 to 29 in lablab, 20 to 22 in green gram, 18 to 19 in black gram, 1 to 5 in cowpea and 1 to 5 kg N/ha in groundnut, respectively. Senaratne et al. (1995) also reported that when cowpea, mung bean and groundnut were intercropped with maize, the proportion of N uptake by maize in the associated legume varied from 7-11% for mung bean, 11-20% for cowpea and 12-26% for groundnut which was about 19 to 22, 29 to 45 and 33 to 60 mg N/maize plant, respectively. The high N2fixation potential of groundnut and its relatively low harvest index for nitrogen apparently contributed to greater beneficial effect on nitrogen uptake of associated crops.
Intercropping was reported to have an impact on the quality of crops (Gangwar and Kalra, 1988;Chittapur et al., 1993;Bulson et al., 1996;Odoemana, 1997). Odoemana (1997) has found that Yam (Dioscorea rotundata) maintained higher value of protein as an intercrop with melon than sole cropping. Similarly, Bulson et al., (1996) reported that in a wheat/faba bean intercropping the nitrogen content of the wheat grain and whole plant biomass increased with the increase in faba bean density, thus resulting in a significant increase in grain protein.
Applications of mineral nutrients to the soil may cause inter specific competition between component crops for the soil based pool of nutrients, may alter the balance in competition between component crops for mineral nutrients and subsequently expressed as competition.
When inter specific competition is less for a nutrient, there will be an increase in LER and total biomass production. This is possible either through enhanced early growth and canopy cover by the mixture or through improved maximum canopy cover or a combination of the two. Data from a pigeon pea /rice mixture showed an increase in LER from 0.85 without phosphorus fertilizer to 1.53 with application of 26.2 kg phosphorous ha-1 and a 60% gain in biomass.
Complementarities in the use of resource which brings about yield advantages in mixture is greater when growth and yield of at least one component crop is somewhat limited and yield potential is low (Chang and Shibles, 1985b). With additional phosphorus in the above-mentioned study, complementarity was less well expressed since increased maize shade caused cowpea yield depression. More attention has been paid to the response of intercropping systems to the application of nitrogen fertilizer because the effect of nitrogen is dramatic particularly in mixture involving legumes. The addition of nitrogen to legume based intercrops generally favors growth of the non-legume at the expense of the legume. With minimal nitrogen, growth of the legume is less restricted than that of the non-legume (Cenpukdee and Fukai, 1991).
Although additional nitrogen directly antagonizes rhizobium N2-fixation in the legume, it enhances lateral (Cenpukdee and Fukai, 1991) and vertical growth of the non-legume component. Greater competitiveness, however, does not necessary result in greater yields, especially in crops or varieties for which the harvest index is very sensitive to high nitrogen (Cenpukdee and Fukai, 1991). However, increased shading over the legume, with increase in competitiveness effected by nitrogen fertilizer application to the non-legume, does reduce the contribution of nitrogen fixation by the legume crop (Chang and Shibles, 1985a), thereby reducing yield compared to mixtures without nitrogen fertilizer. Where the legume is responsive to added nitrogen and has the opportunity to shade the non legume crop, yields of the non-legume may effectively decline at higher nitrogen application rates (Olasantan, 1991), consequently, only at low soil N status (0 to 30 kg N ha-1) was complementarity of intercrops, as indicated by large LER. The response of intercrops to added nitrogen is conditioned by factors such as soil moisture availability, plant population, and canopy structure of component species, and differential temporal demands for nitrogen by component crops. For instance, inconsistent effects of nitrogen fertilization on the relative competitive abilities of maize and soybean across sites have been attributed to difference in soil moisture and nitrogen availability (Russell and Caldwell, 1989). Under limited soil moisture, partial LERs of maize increased, while those of soybean decreased under increased fertilizer nitrogen over range of density combinations. Under the same environmental conditions, where crops exhibited visible signs of stress the optimum density combinations were dependent up on N levels, whereas at a contrasting moisture site the optimum combinations were unchanged over N levels.
The combination of high population density of maize and high fertilization caused shading and yield depression of cowpea when intercropped with maize (Chang and Shibles, 1985b). This finding, together with data from the studies of Ofori and Stern (1987) suggest that intercropping efficiency is greater under low than high fertility.

Materials and Methods
The experiment was conducted in dry season under irrigation in Fogera Plain, South Gonder Zone, Ethiopia to study the biological benefits of maize (Zea mays L) intercropping with fenugreek, field pea and haricot bean as compared to their sole crops. The materials and methods used during the course of experimentation are described in details in the following sub chapters.

Description of the Study Area
The present study was carried out in Fogera Plain, South Gonder Zone, Ethiopia. The experiment was specifically conducted Dera District in Jigna rural village, which is located at 42.16 km North of Bahir Dar city at the longitude, latitude and altitude of 19 0 37' E, 11 0 51' N and 1807 m.a.sl, respectively. The mean annual temperature of the experimental site is reported 17.5°C with 10°C and 28°C minimum and maximum temperatures, respectively. The site receives average total rainfall of 1250mm annually with summer main rainy season occurring from May to September, peak in June, July and August (WoRA, annual report 2012).

Figure 1. Map of the study area (source BoFED).
Topography of the experimental site is plain, and its soil type is largely clay loam. Before planting, composite soil sample was collected from the experimental plot and analyzed in the soil laboratory of Amhara Design & Supervision Works Enterprise, Soil Chemistry and Water Quality Section to determine some of its physico-chemical properties. The composite sample was air dried, grounded and sieved for further analyses of soil pH, texture, total nitrogen, organic carbon and available phosphorous using respective standard procedures. The soil pH was measured with digital pH meter potent metrically in the supernatant suspension of 1: 2.5 soils to distilled water ratio. Total nitrogen was determined following Kjeldahl procedure as described by Cottenie (1980). Organic carbon was determined following wet digestion method as described by Walkley and Black (1934), while the available phosphorus was measured using Olsen II methods (Olsen et al., 1954). The laboratory soil analysis results are presented here below in Table 1.

Experimental Treatments and Design
The experimental plot was selected near to Gumara River to ease irrigation. Before planting, uniform seedbed was prepared by plowing the land three times using local oxen plough as the practice of local farmers. Seed sowing was made properly as per the plan of experimental treatments and sowed on 25 December 2012. Three intercrops of maize with fenugreek, haricot bean and field pea, as well as, their four sole crops were the treatments of the experiment ( Table 2). The treatments were laid out under randomized complete block design (RCBD) at three replications. Planting materials used for the experimentation were selected based on their height to minimize shade effect and tolerance of hot and high temperature relatively to the other varieties of the same crop to minimize irrigation frequencies.
Hence, BH540 hybrid has short height in maize and Challa, Burkitu and Awash Melkassa varieties are relatively tolerance to hot and high temperature of fenugreek, field pea and haricot bean, respectively. The plot size of each treatment was 3 m × 2.7m (8.1m 2 ). Spacing between replications and Field Pea and Haricot Bean Under Irrigation in Fogera Plain, South Gonder Zone, Ethiopia plots was 1.5m and 1.0m, respectively. Number of rows per plot for maize in both intercropping and sole cropping was 5, and seed per row was 10 while number of rows per plot for fenugreek, field pea and haricot bean in the sole cropping was 16, 16 and 8, respectively. Seed planted per row for fenugreek and field pea was 55 and for haricot bean was 28. Indeed, all fenugreek, field pea and haricot bean were planted in a single row between maize rows with total 4 rows each per maize intercropping plot. The recommended inter-and intra-row spacing was used for all experimental crops. Maize inter-and intra-row spacing was 75cm × 30cm, while for fenugreek, field pea and haricot bean, inter-and intra row spacing was 20cm × 5cm, 20cm × 5cm and 40cm × 10cm, respectively. Only intra-row spacing was applied for the secondary crops of intercropping plots.
Planting rows were marked with pegs at recommended inter-row spacing of each crop and lined with strings. Sowing of seeds was made manually along stretched strings at recommended intra-row spacing of the crops. All recommended DAP amounted 100kg/ha and half of the recommended Urea (50kg/ha) were applied in side banding of few centimeters away from maize rows at planting. Half of the Urea (50kg/ha) was divided equally into two and side dressed to maize rows at knee height and booting growth stages. In addition to this for secondary crops DAP 100kg/ha and urea as a starter 50kg/ha base were applied at planting time. Crops were irrigated in every week for a month in the early time of growing and later every 10 days as per farmers experience in the study area. However, there was water scarcity due to drying off "Gumara" river especially at the blister stage of maize crop and it doesn't give the expected yield, while the other crops matured earlier and escaped from the water scarcity. Two times of hand weeding were carried out before the flowerings of crops.

Data Collection
Phenological, growth and yield related parameters of experimental crops were recorded following their respective days of emergence, flowering, maturity, number of cob/ pod per plant, seed per pod/cob, yield per plot, thousand grain and biomass weight following standard methods and procedures. In all cases, plants found on the borders of experimental plots were excluded from any data collection, while border effects would mar the actual effects of the treatments. Parameters were hence collected from 10 randomly selected plants of the net plot areas.
Phenological parameters including day of seedling emergence and day of flowering were recorded when 50% of plants per plot reached their respective phenological stages. Day of maturity was recorded also when 90% of plants per plot attained their physiological maturity of maize at early dent stage and pods of fenugreek, field pea and haricot bean turned yellow to yellowish-brown colour.
Excluding boarder row plant height of 10 randomly selected tagged plants were measured per plot area of each experimental from the ground level to the initiation of tassel and for the second crops from the ground to leaf axils or flower initiations with linear meter (cm) during physiological maturity period and its average value was used for further analysis. Similarly, number of cobs or pods per plant was also counted and averaged from the 10 randomly selected plants. Number of seeds per cob or pod was also counted and averaged from cobs/pods of 10 randomly selected plants per plot. A different 10 randomly selected plants of each crop per plot were harvested at their 90% maturity and sun dried very well to measure their dry biomass with sensitive electrical balance in gram (g) and converted into hectare basis in kilo gram (kg). After measuring their dry biomass, randomly selected plants per plot were threshed manually and their grain yield was measured with sensitive balance in grams and converted into hectare basis to express in kg. Thousand seeds were also selected from grain yield of 10 selected plants and measured with sensitive balance to determine 1000 seeds weight which is expressed in gram. Both grain yield and 1000 seeds weight were adjusted at 12.5% for maize and 10.5% moisture content for all secondary crops (source Ethiopian seed enterprise).

Data Analysis
The analysis of variance (ANOVA) was carried out using statistical packages and procedures out lined by Gomez and Gomez (1984) appropriate to Randomized Complete Block Deign using SAS (Statistical Analysis Software) version 9.2 Whenever the ANOVA results showed significant difference between treatments, mean separation was further carried out using Duncan's Multiple Range Test (DMRT) at respective levels of error.
Correlation analysis was also carried out to study the nature and degree of relationship between yield and yield components as influenced by intercropping. Correlation coefficient values (r) were calculated and test of significance was analyzed using Pearson correlation procedure found in SAS software.
Pearson correlation method was selected due to it is widely used in the sciences as measure of the degree of linear dependence between two variables. It measures the strength of the linear relationship between normally distributed variables. In statistics the person correlation coefficient is a measure of the linear correlation between two variables X and Y giving a value between +1 and -1 inclusive, where 1 is a total positive correlation, 0 is no correlation, and -1 is total negative correlation.

Results and Discussion
The results and major findings of the present study are presented and discussed below in this chapter. Effect of maize intercropping with fenugreek, field pea and haricot bean on phenology, vegetative growth and yield parameters is separately discussed in this chapter.
Crop Phenology Effect of maize intercropping with fenugreek, field pea and haricot bean on crop phenology is presented in Table 3. Maize as sole and intercropping with fenugreek, field pea and haricot bean was emerged within 12, 16, 12 and 15 days after sowing, respectively (Table 3.). Similarly, it took 89, 91, 91 & 85 days to flowering and 135, 139, 136 and 132 days for maturation, respectively. Statistically, interand sole-cropping did not affect significantly (p>0.05) 50% days of emergence, flowering and maturity of maize (Table  3.). The reason for the lack of significance difference of inter-and Sole-cropping for maize phenology could be due to less competitive effect of the associated legumes on maize.
Similar to the present finding, Karikari et al. (1999) in an intercropping experiment involving Bambara groundnut and cereals including sorghum, pearl millet and maize reported that days to flowering was not differed significantly between the sole crop and the intercropped cereals. Similarly, the report of Yesuf (2003) also indicated that the effect of sorghum-haricot bean intercropping on days to 50% flowering of sorghum was not statistically significant.
Likewise, Tilahun (2002) in maize -faba bean intercropping reported also no variation in days to silking and tasseling of maize. Similar results were also reported by Yesuf (2003) and Sisay (2004) that day to 50% maturity of sorghum was not significantly affected by both sorghum-bean and sorghum-green gram intercropping.
The analysis of variance for effect of inter-and solecropping on fenugreek phonological parameters didn't show any significant differences at 5% acceptable level of experimental error. However, as compared with that of sole cropping; intercropping caused for the delay of fenugreek emergence on average by six days (Table 3.). Early emergence of fenugreek in sole cropping might be due to the fact that sole fenugreek had advantage over intercropping for reduction of competition for growth factors. On the contrary, all intercropped fenugreek plots flowered and matured earlier than that of sole fenugreek plots.
In disagreement of the present results, Karikari et al. (1999) reported that sole Bambara groundnut flowered in a significantly shorter period than that of the intercropped one. Sisay (2004) also reported that though the difference was not significant statistically, sole green gram took the least days (45 days after emergence) to flower, while its mean days to flowering in the intercropping was 51.
The contrast results of the present study to other similar reports on the duration of flowering in sole and intercropped legumes would perhaps be associated with moisture stress that occurred frequently in the present experiment. In a condition where there was moisture stress intermittently, fenugreek as the second crop in the intercropped plots might serve as a live mulch reduce the loss of water relatively better than that of its sole cropping. Besides, the tall maize crop shaded over fenugreek at least partially and thereby fenugreek intercropped with maize might not be affected by moisture stress as worse as that of its sole cropping. Hence, growth of fenugreek plants in maize intercropping might not be retarded equally by intermittent moisture stress as that of sole cropping. This might in turn result in early flowering and maturity of intercropped fenugreek plants more than that of sole fenugreek plants.
Except days of 50% emergence of haricot bean, sole and intercropped field pea and haricot bean surprisingly emerged, flowered and matured in almost respective similar days ( Table 3). The sole haricot bean was indeed emerged 5 days earlier than that of intercropped one. Early emergence of haricot bean seedlings in sole cropping might be associated with lower competition for light in sole cropping than in its intercropping with maize.
Indeed, this present result was different from results of similar works reported by Karikari et al. (1999) and Sisay (2004) as indicated above on Bambara groundnut and green gram, respectively.

Growth and Yield Components
The analysis of variance indicated that effects of intercropping had no significant difference (p>0.05) on plant height, cob number per plant and seed per cob of maize. However, thousand grain weight of maize was affected significantly (p<0.05) by intercropping (Table 4). Similar to this finding, Zewdu (2002) and Sisay (2004) reported the non-significant effect of intercropping on plant height of sorghum at harvest. Yesuf (2003) also found that plant height of sorghum was not statistically different in intercropped and sole sorghum. In a maize and cowpea intercropping experiment, Wanki and Fuwusi (1982) discovered that plant height of maize was not affected due to intercropping. Amare (1992) also reported that in maize haricot bean intercropping, plant height of maize in intercropped treatments did not differ significantly with that of sole maize.
In contrary to these findings, Ibrahim et al. (1993) found that growth parameters such as plant height and number of internodes were significantly higher in intercropped sorghum with lablab (Lablab purpureus L.) than in sole sorghum cropping.
In other studies, it was also reported that the difference in plant height of the cereals in intercropping was not significant in Bambara groundnut + sorghum and Bambara groundnut + maize mixtures but it was significant in Bambara groundnut + pearl millet intercropping (Karikari et al., 1999).
This contradiction could be due to the difference in the nature of intercrops involved particularly of legumes species incorporated to the system because legumes differ in their competitive abilities against to the cereal component for the limited growth factors.
The difference in plant height, pod number per plant, seed per pod and thousand grain weight of the sole and intercropped fenugreek was not significant (p>0.05) ( Table  4.). However, the sole fenugreek produced higher number of pods or seed per plant and slightly greater in plant height and thousand grain weight compared to the intercropped fenugreek (Table 4.).
The difference in plant height, pod per plant, seed per pod and thousand grain weight of the sole field pea and haricot bean with intercropped field pea and haricot bean was not statistically significant (P>0.05) ( Table 4.). However, there was slight difference in height between the intercropped field pea and sole field pea. The intercropped field pea was greater than that of sole for height. This could be associated with less moisture stress effect of intercropping on field pea than that of sole field pea, while maize might partially be having shade effect on the soil and on the secondary crop field pea that might not be subjected to serious moisture stress caused by shortage of irrigation water during the growing period as compared to that of sole field bean. Similarly, this condition was also observed on plant height and thousand grain weight of intercropped haricot bean that were slightly greater than that of the sole cropping (Table 4.).
The results obtained in this study are in agreement with that of Davis and Garcia (1987) who reported reduction in hundred seed weight of haricot bean in maize intercropping as compared to that of sole cropping perhaps due to competition exerted by maize plants.
In agreement with the present finding, Sisay (2004) reported that seed weight of green gram per plant in the intercropping was 93.0mg as compared to that of 52.0mg in the sole cropping.

Biomass and Grain Yields
Grain yield and biomass of maize, fenugreek, field pea and haricot bean as influenced by intercropping and sole cropping are presented below in Table 5. The analysis of variance revealed that intercropping of maize with fenugreek, field pea and haricot bean didn't significantly (P>0.05) affect the grain yield, however significant effect on biomass of maize was observed (Table 5.).
The grain yield and biomass of sole maize were superior than that of intercropping (Table 5.). These higher differences between the sole-and inter-cropping for maize grain yield and biomass would be associated with competition between the main and secondary crops in the intercropping for limited growth resources.
Similar to the current finding, Shehu et al. (1999) reported that monocropping resulted in superior grain yield of maize/sorghum compared with different intercropping treatments. Also, Pal et al. (1993) reported that seed yields of monocrops of soybean, maize and sorghum were higher than their respective encounters in the intercropping. They ascribed this yield variation in the intercropping to the high plant density per unit cultivated area. The finding of Tamado and Eshetu (2000) also revealed that sorghum grain yield in sole cropping was higher than that of the intercropping. Yesuf (2003) reported also that significant grain yield reduction on sorghum crop was recorded in the intercropping compared to that of sole cropping.
According to him, sorghum suffered with yield reduction due to its intercropping with beans. Sisay (2004) also reported that the effect of sorghum planting patterns and its interaction with green gram density on sorghum panicle weight per plant was not significant. The same author reported no significant difference between intercropping and sole cropping for sorghum yields.
Likewise, Tamado and Eshetu (2000) reported that panicle weight per plant of maize/sorghum was not significantly affected by intercropping with haricot bean. Similarly, Carr et al. (1992) reported that grain yield of sorghum was similar whether monocropped or intercropped with varying population of beans. In an intercropping experiment involving 50% and 100% the normal population of sorghum and the legumes green gram, red gram, and soybean, in a paired row system, Hunshal and Malik (1985) reported that the different intercrops did not have any adverse effect on yield and yield components of sorghum.
A study on the effect of population density and planting arrangement on maize or sorghum-pigeon pea intercropping also indicated that row spacing and planting methods did not show significant effect on maize/sorghum yield at an optimum plant population of 180,000 plants/ha. Rather, intercropping pigeon pea in maize/sorghum rows, gave an additional 342 kg/ha of pigeon pea without causing significant yield reduction in sorghum (Balearic and Pathway, 1981).
However, Bandyopadhyay and De (1986) reported higher maize/sorghum yields in their mixture with green gram or cowpeas than that of their sole cropping due to greater Field Pea and Haricot Bean Under Irrigation in Fogera Plain, South Gonder Zone, Ethiopia panicle, more grain per panicle, and weight. The authors attributed this highest sorghum grain yield in the intercropping to greater panicle and thousand-grain weight.
In addition, Sharanappa and Hosmani (1987) reported that highest grain yield of sorghum was obtained in sorghum intercropping with paired rows of green gram. Concerning biomass of fenugreek, field pea and haricot bean, the analysis of variance showed that there has significant difference (p≤0.05) between intercropping and sole cropping while for grain yield had no significant difference on fenugreek, field pea and haricot bean intercropping ( Table 5).
The sole fenugreek, field pea and haricot bean produced slightly higher grain yield and biomass per hectare compared to the intercropped ones. The highest yields and biomass of field pea and haricot bean amounted for yield 2826kg/ha and 2399kg/ha, and 2667.9kg/ha and 2596kg/ha for biomass respectively, were recorded in the sole crops. High grain yield of fenugreek, field pea and haricot bean in the sole cropping more than that of intercropping could be due to competition exerted by maize component for growth factors (Table 5.).
However, thousand grain weight of haricot bean in the sole cropping was less than that of the intercropping (Table 4).
Similar to this finding, Demesew (2002) reported that grain yield per hectare of haricot bean was not affected significantly (P>0.05) by intercropping. The results obtained in this study are in disagreement with that of Davis and Garcia (1987) who reported reduction in hundred seed weight of haricot bean in maize intercropping as compared to that of sole cropping. This was perhaps associated with competition exerted by maize plants for resources.
The combined analysis of variance of maize, fenugreek, field pea and haricot bean as influenced by intercropping showed no significant difference (p>0.05) both in biomass and yield (Table 6).

Conclusion and Recommendations
This experiment was conducted to assess the biological benefits of intercropping maize with fenugreek, field pea and haricot bean in irrigated fields of Fogera Plain during the dry season. There were no any significant differences between sole and intercropping of maize with fenugreek, field pea and haricot bean for phenological parameters including days to 50% crop emergence, flowering and maturity. Except dry biomass yield most growth and yield components including pod/cob per plant, plant height and seed per pod were not significantly influenced by maize intercropped with fenugreek, field pea and haricot bean.
Generally, the sole maize was slightly higher than the intercropped one in all parameters except thousand grain weight. Sole fenugreek was also slightly higher than the intercropped one in all parameters. On the contrary, intercropped field pea produced higher pod per plant, plant height and seed per pod than that of sole field pea, although it was vice versa in all other parameters. Haricot bean in the intercropping produced also slightly higher plant height, seed per pod and thousand grain weights than its sole crops. Indeed, sole haricot bean was slightly higher than the intercropped one in all other parameters. Generally, in this experiment the biological (biomass) benefit was observed.
However, from the forgoing results, intercropping on biological parameters of main crop (maize) and the secondary crops (fenugreek, field pea and haricot bean) yield per hectare was improved by the use of intercropping of maize with haricot bean and field pea at Jigna rural village Dera District, south Gonder area under irrigation in dry season.
Similar studies are strongly recommended for further to develop extension packages.