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REVIEW OF LITERATURE
Intercropping of cereals and grain legumes is a neglected theme in agricultural science and practice in both conventional and organic farming systems (Dahlmann, and Von Fragstein2006). The fast rising population in many tropical countries is one of the reasons for enormous growing demand for food. The increasing urbanization due to world growing population has affected food production leading to irrevocable loss of arable land. Opening up new land for cultivation can enhance the decrease of agriculture. Farmers and researchers should be conscious that cost-benefit ratio bringing new land under cultivation is smaller than that of increasing production of already cultivated land, which may lead to increase in production per unit area.
Intercropping tenders farmers the opportunity to engage nature's principle of diversity on their farms. Spatial arrangements of plants, planting rates, and maturity dates must be considered when planning intercrops. Intercrops can be more fruitful than growing monocropping. Many different intercrop systems have been studied, including mixed intercropping, strip cropping, and customary intercropping provisions. Pest management benefits can also be realized from intercropping due to augmented diversity. Harvesting options for intercrops include hand harvest, machine harvest for on-farm feed, and animal harvest of the standing crop. Most grain-crop mixtures with similar ripening times cannot be machine-harvested to produce a marketable commodity since few buyers purchase mixed grains. Dispite its advantages intercropping is neglected due to complex nature of intercropping systems.
In intercropping systems an LER measures 1.0, it tells us that the amount of land required for crops grown together is the same as that for these grown in pure stand (i.e., neither loss nor loss due to intercropping over pure stands). LERs above 1.0 demonstrate an advantage to intercropping, while numbers below 1.0 diplay a disadvantage to intercropping. For example, an LER of 1.25 tells us that the yield produced in the total intercrop system would have required 25% more land if planted in pure stands. If the LER was 0.75, we know the intercrop yield was only 75% of that of the same amount of land that grew pure stands.
Pakistan is a subtropical country having sufficient resources with high intensity of sunlight required for plant growth. Therefore, possibility of intercropping of different crops on the same piece of land in a year needs to be explored for effective and efficient utilization of these natural resources. Intercropping is being looked as an efficient utilization of these natural resources and economical production system as it increases the production per unit area and time. Presently, interest in intercropping is increasing among the small growers because of their diversified needs and meagre farm returns from the monocropping system.
Planning of cropping system should be done yearly on entire catchment basis. The type of planning should lead to a proper balance between food, fiber and fodder crops. When the rainfall is between 500-700 mm with a distinct period of moisture surplus, intercropping system should be adopted for improved crop production. Even in higher rainfall areas (750- 1100 mm) intercropping facilitates growing either cereal-legume or legume-legume system of different maturity patterns. Intercropping minimize risk of crop failure in drylands. Mixed cropping (mixing seeds of two or more crops and broad casting the mixture) should be avoided as it hinders post-sowing operations. Choice of varieties with in the crops is very important to harness total intercropping advantage. Cereal-legume intercropping systems should be advocated to minimize fertilizer use,.? reduce pest and disease incidence,?? produce balance foods, ?provide protein rich legume fodder for cattle,? take full advantage of growing season.
Cereal-legume intercropping plays an important role in subsistence food production in both developed and developing countries, especially in situations of inadequate water resources (Tsubo et al., 2005). Intercropping cereals and grain legumes can be very potential for both organic and conservative farmers. The use of land equivalent ratio (LER) as a measure for calculating the cropping advantage of intercrops over sole crops is simple, ignoring weed inhibition, yield reliability, grain quality, and minimum advantageous yield are all relevant factors for farmers' perspective (Prins and de Wit 2005).
Intercropped legumes secure most of their nitrogen from the atmosphere and not compete with maize nitrogen resources (Adu-Gyamfi et al. ,2007). Increased diversity of the physical structure of plants and increased leaf cover in an intercropping system facilitates to reduce weed infestations once crop are established (Beet1990). Having a variety of root system in the soil reduces water loss, enhances water uptake and reduce transpiration. The increased transpiration may make the microclimate cooler, which cools the soil and decrease evaporation (Innis 1997). In this way during times of water stress, intercropped plants utilize a larger percentage of available water from the field than monocropped plants. Creating windbreaks may also modify the microclimate. Rows of maize in a field with a short stature crop would reduce wind speed above the shorter crop and thus deceasechance of desiccation (Beet1990). Intercropped legumes fix most of their nitrogen from the atmosphere and not compete with maize for nitrogen resources (Adu-Gyamfi et al. ,2007; Vesterager et al.,2008).
Diversification of cropping systems, i.e. smaller fields and mixtures of crop species (intercropping) was much more in vouge Pre World War II. Intercropping, the simultaneously cultivation of more than one species in the same field, is a cropping method, which often result in a more efficient use of resources, cause more stable yields in problematic environments and a method to reduce problems with weeds, plant pathogens and nitrogen losses post grain legume harvest.In this context a greater introduction of longterm rotations, intercrops and grain legumes play an important role (Jensen 1997; Karlen1994). Intercropping of cereal and legume crops facilitates to maintain and improve soil fertility (Andrew, 1979).
Intercropping of legumes with cereals has been popular in tropics (Hauggaard-Nielsen et al.,, 2001; Tsubo et al.,,2005) and rain-fed tracts of the globe (Banik et al.,, 2000; Ghosh, 2004; Agegnehu et al.,, 2006; Dhima et al.,,2007) due to its benefits for soil conservation (Anil et al., 1998), weed control (Poggio, 2005; Banik et al.,,2006), lodging resistance (Anil et al.,, 1998), yield enhancemnent (Anil et al.,, 1998; Chen et al.,, 2004), hay curing, forage preservation over pure legumes, more crude protein percentage and protein yield (Qamar et al.,, 1999; Karadag and Buyukburc, 2004), and contols legume root parasite infections (Fenandez-Aparicio et al.,,2007).
Different seeding ratios or planting patterns for cereal-legume intercropping have been accomplished by many researchers (Tsubo et al.,, 2001; Karadag and Buyukburc, 2004; Banik et al.,, 2006; Dhima et al.,, 2007). Competition among mixtures is thought to be the major characteristic affecting yield as compared with monocropping of cereals. Species or cultivar selections, seeding ratios, and inter and intra specific competition among mixtures may influence the growth of the species grown in intercropping systems in rain-fed areas (Santalla et al.,, 2001; Karadag and Buyukburc, 2004; Carr et al.,, 2004; Agegnehu et al.,, 2006; Banik et al.,, 2006; Dhima et al.,, 2007).
Various competition indices such as land equivalent ratio (LER), relative crowding coefficient (RCC), competitive ratio (CR), actual yield loss (AYL), monetary advantage(MI) and intercropping advantage(IA) have been anticipated to portray competition within and economic advantages of intercropping systems (Banik et al.,, 2000; Ghosh, 2004; Agegnehu et al.,, 2006; Banik et al.,, 2006; Dhima et al.,, 2007). However, such indices have not been used for maize and common bean intercropping to determine the competition among species and also economic advantages of each intercropping system in the East Mediterranean region. Higher monetary returns were obtained compared to sole cropping when bush beans intercropped with sweet maize (Santalla et al.,, 2001). Higher seed yield and net income under planting pattern with changing mix-proportions may be explained in higher total productivity under intercropping with relatively less input investment (Banik et al.,, 2006).
Tsubo et al., (2005) formed a simulation model to find out the best planting methods for maize and bean intercrops in sub-arid South Africa. Based on 52 years of weather data, they compared the best planting time, optimal water saturation at planting, maize plant density, and bean plant density to receive the highest LER, energy value (EV), and monetary value (MV) from the intercropped field. For every combination of factors, a LER greater than 1.0 was found, indicating that intercropping of maize and beans increases total yield. The simulations show that initial soil water content has the greatest influence on intercropping productivity. Bean plant density had no influence on maize or bean yields, indicating that maize yield is not affected by bean intercropping, although bean yields were decreased in the intercropped system (Tsubo et al., 2005). High densities of maize maximized maize yield and calorie production, but high densities of beans maximized financial return. Decline of external inputs and increases of homegrown feed together with a more efficient nutrient use from leguminous symbiotic dinitrogen (N2) fixation (SNF) can result in a decrease of nitrogen and mineral losses. Maize-legume intercropping systems are able to lessen amount of nutrients taken from the soil in comparasion to a maize monocrop.
Organizing the complication of exchanges that are possible due to the physical constraints of diversity are present in the farm system is vital part of reducing the need for external inputs and moving toward sustainability (Herrera, 1974). Increasing diversity often allows better resources use efficiency in agro ecosystem because with higher diversity, there is larger microhabitat differentiation, allowing the components species and varieties of the system to grow in an environment ideally fitting to its unique requirements (Mazaheri and Oveysi, 2004; Willey and Reddy1981; and Yancey, 1994). A key and straight way of rising diversity of an agro ecosystem is intercropping system that allows interaction between the individuals of the different crops and varieties (Mazaheri, 2004; Willey, 1981 and Venkatswarlu1981).
Intercropping can add temporal diversity through the sequential planting of different crops during the same season (Yancey, 1994). Importance of multiple cropping is increasing world food supplies. An LER value of 1.0, indicating no difference in yield between the intercrop and the collection of monocultures (Mazaheri and Oveysi, 2004 and Kurata 1986). Any Value greater than 1.0 indicates a yield advantage for intercrop. A LER of 1.2 for example, indicates that the area planted to monocultures would need to be 20% greater than the area planted to intercrop for the two to produce the same combined yields (Laster and Furr,1972). Intercropping in cassava was beneficial in increasing the biological yield, tuber equivalent yield and land use efficiency. Cassava tuber equivalent yield, LER, ATER and AHER were higher in cassava + cowpea combinations.(Amanullah et al., 2006). Mixed culture (or intercropping) of legumes and cereals is an old practice in tropical agriculture that dates back to ancient civilization. The main objective of intercropping has been to maximum utilization of resources such as space, light and nutrients (Willey, 1990; Morris and Garrity, 1993; Li et al.,, 2003b), as well as to improve crop quality and quantity (Nel, 1975; Izaurralde et al.,, 1990; Mpairwe et al.,, 2002).
Other benefits include water quality control through least use of inorganic nitrogen fertilisers that pollute the environment (Crew and Peoples, 2004). The contemporary drift in global agriculture is to search for highly productive, sustainable and environmentally safe cropping systems (Crew and Peoples, 2004). This has resulted into renewed interest in cropping systems research (Vandermeer, 1989). When two crops are grown in association, interspecific competition or facilitation between plants may take place (Vandermeer, 1989; Zhang et al.,, 2003).Different studies have shown that mixtures of cereals and legumes produce higher grain yields than either crop grown unaccompanied (Mead and Willey, 1980; Horwith, 1984; Tariah and Wahua, 1985; Ofori and Stern, 1987a; Lawson and Kang, 1990; Watiki et al.,, 1993; Peter and Runge-Metzger, 1994; Skovgard and Pats, 1999; Rao and Mathuva, 2000; Olufemi et al.,, 2001; Mpairwe et al.,, 2002; Dapaah et al.,, 2003). In such crop mixtures, the yield increases were not only due to enhanced nitrogen nourishment of the cereal component, but also to other unexplored causes (Nel, 1975; Connolly et al.,, 2001).
Many of the unknown and less research processes occur in the rhizosphere of mixtures (Connolly et al.,, 2001; Zhang et al.,, 2003, 2004). The rhizosphere soil is the narrow zone of soil neighboring the roots where soil, micro-organisms and roots jointly play key roles in the soil ecosystem. Compared with the bulk soil, the rhizosphere has diverse biological, physical and chemical soil properties. It is rich in root exudates, and, therefore, play a major role in nutrient mobilisation and microbial activities (Dakora and Phillips, 2002; Dakora, 2003). So far however, little attention has been paid to rhizosphere effects on crops grown in mixtures (Connolly et al.,, 2001; Zhang et al.,, 2003; 2004), where interaction between different organisms is high. The major management practices employed in mixed cultures to attain good yield includes the enhancement of microclimatic conditions, improved utilisation and recycling of soil nutrients, improved soil quality, provision of favourable habitats for plants and stabilisation of soil, among others (Juma et al.,, 1997).
Most of intercropping systems are intentionally made and manipulated to optimise the use of spatial, temporal, and physical resources both above-and belowground, by maximising positive interactions (facilitation) and minimizing negative ones (competition) among the components (Willey and Osiru, 1972; Willey, 1979; Mead and Willey, 1980; Horwith, 1985; Ofori and Stern, 1986, 1987a, b; Jose et al.,, 2000; Silwana and Lucas, 2002). An understanding of the biological and chemical processes and mechanisms involved in the distribution of resources in such systems is indispensable. The complex interactions in legume/cereal cropping systems such as those used by traditional farmers have received little research attention (Connolly et al.,, 2001; Zhang et al.,, 2004) because quantitative rhizosphere studies in the field involving complex mixtures are notoriously complex and cumbersome. These conditions are achieved by manipulating management practices such as planting patterns of the mixtures with the selection of appropriate cropping systems.
Interactions will occur in the growth process, especially when the component species are exploiting the resources above-and below-ground (Vandermer, 1989; Willey, 1990; Ong et al.,, 1996) from the same niche or at the same time. In crop mixtures, any species utilizing the same combination of resources will be in direct competition. However, based on differences in phenological characteristics of species in asocition, the interaction among them may lead to an increased capture of a limiting growth resource (Willey and Osiru, 1972; Willey, 1979; Mead and Willey, 1980; Horwith, 1985; Ofori and Stern, 1986, 1987a,b; Silwana and Lucas, 2002) and then amassing larger total yield than the collective production of those species if they were grown separately on an equivalent land area (Mead and Ndakidemi 2527 Willey, 1980; Horwith, 1984; Tariah and Wahua, 1985; Ofori and Stern, 1987a; Lawson and Kang, 1990; Watiki et al.,, 1993; Peter and Runge-Metzger, 1994; Myaka, 1995; Asafu-Agyei et al.,, 1997; Skovgard and Pats, 1999; Rao and Mathuva, 2000; Olufemi et al.,, 2001; Dapaah et al.,, 2003). Thus, mixed cropping systems between cereals and legumes may face a complex series of inter- and intra-specific interaction (Izaurralde et al.,, 1990; Giller and Cadisch, 1995; Evans et al.,, 2001; Li et al.,, 2003c) geared by modifications and utilisation of light, water, nutrients and enzymes.
Most annual crop mixtures such as those involving cereals and legumes are grown almost at the same time, and develop root systems that acquire the same soil zone for resources (Horwith, 1984; Chang and Shibles, 1985a,b; Reddy et al.,, 1994; Jensen et al.,, 2003). Under such circumstances, below-ground competition for resources such as nutrients is most likely to take place. For example, research has shown that activities in maize + cowpea intercropping take place between the top 30-45 cm of soil, and their intensity decreased with depth (Maurya and Lal, 1981; McIntyre et al.,, 1997). Because of these interactions, cowpea yields can be reduced significantly in relationto that of maize (Watiki et al.,, 1993).
In contrast to some negative effects on yield, root systems in mixtures may provide some of the major favorable effects on soil and plants. These include, amongst others, carbon enrichment through higher carbon return (Ridder et al.,, 1990; Vanlauwe et al.,, 1997), discharge of phenolics, phytosiderophores and carboxylic acids as root exudates by companion plants (Dakora and Phillips, 2002; Dakora, 2003). These compounds play a major role in the mineral nutrition of plants. For instance, some studies have displayed that, in P-deficient soils, pigeon pea roots utilize piscidic, malonic, and oxalic acids to solubilise Fe-, Ca- and Al-bound P (Ae et al.,, 1990). Once mobilised, P and Fe then become available for uptake by the pigeon pea plant as well as by plant species grown in association and micro flora in the cropping system.This is due to the fact that, thus far, research efforts on mixed cultures has centered on the intra- and inter-specific competition for light and water, and research reports on competition for nutrients in legumes and cereal mixtures (Connolly et al.,, 2001; Zhang et al.,, 2003, 2004). It is, therefore, imperative to discover how the rhizosphere systems of the associated plant species in mixtures interact under different legume-cereal cropping systems.
Rhizospheric pH changes in different management systems in legume/cereal mixtures
Many plants have the ability to alter the pH of their rhizosphere (Hoffland et al.,, 1989, 1992; Raven et al.,, 1990; Degenhardt et al.,, 1998; Muofhe and Dakora, 2000; Dakora and Phillips, 2002) and improve nutrient availability such as P, K, Ca, and Mg, which are otherwise fixed and not available to plants (Vandermeer, 1989; Hauggaard- Nielson and Jensen, 2005). For instance, legumes induce numerous reactions that modify the rhizosphere pH (Jarvis and Robson, 1983; McLay et al.,, 1997; Tang et al.,, 1998, 2001) and influence nutrient uptake (Brady, 1990; Vizzatto et al.,, 1999). For example, Dakora et al., (2000) have shown that due to pH changes in the rhizosphere, Cyclopia genistoides, a tea-producing legume native to South Africa, increased nutrient availability in its rhizosphere by 45 - 120% for P, 108 - 161% for K, 120 - 148% for Ca, 127 - 225% for Mg and 117 - 250% for boron (B) compared to bulk non-rhizosphere soil. Hence, legumes may take up higher amounts of base cations, and in the process of balancing internal charge, release H+ ions into the rhizosphere that results in soil acidification (Jarvis and Robson, 1983; McLay et al.,, 1997; Tang et al.,, 1998, 2001; Sas et al.,, 2001; Dakora and Phillips, 2002; Cheng et al.,, 2004).
Other legumes such as alfalfa, chickpea, lupines, and cowpea can release considerable amounts of organic anions and lower their rhizospere pH (Liptone et al.,, 1987; Dinkelaker et al.,, 1989, 1995; Braum and Helmke, 1995; Gilbert et al.,, 1999; Neumann et al.,, 1999; Rao et al.,, 2002; Li et al.,, 2004b), a condition favorable for the hydrolysis of organic P and hence improving P2O5 nutrition for plants and micro organism in the soil. In the same context, white lupine (Lupinus albus) exuded organic acids anions and protons that lowered rhizosphere pH and recovered substantial amount of P2O5 from the soil and made them more available to wheat than when it was grown in solitary cropping system (Horst and Waschkies, 1987; Kamh et al.,, 1999). Similarly, pigeon pea increased P2O5 uptake of the intercropped sorghum by exuding piscidic acid anions that chelated Fe3+ and subsequently released P2O5 from FePO4 (Ae et al.,, 1990). In a field trial, faba bean facilitated P2O5 uptake by maize (Zhang et al.,, 2001; Li et al.,, 1999, 2003b; Zhang and Li, 2003). In another comparative study, the ability of chickpea to mobilise organic P2O5 was shown to be greater than that of maize due to greater exudation of protons and organic acids by chickpea in relation to maize (Li et al.,, 2004a). Thus, in mixed cultures, plants such as cereals, which do not have strong rhizosphere acidification capacity can benefit directly from nutrients solubilised by legume root exudates. What is, however, not clearly known is the extent of rhizosphere pH changes in mixed cultures involving nodulated legumes and cereals and their influence on other biological and chemical processes in the soil.
N2 FIXATION IN LEGUMES AND THE ASSOCIATED
BENEFITS TO THE CEREAL COMPONENT
Biological nitrogen fixation by grain legume crops has received a lot of attention (Eaglesham et al.,, 1981; Giller et al.,, 1991; Izaurralde et al.,, 1992; Giller and Cadisch, 1995; Peoples et al.,, 2002) because it is a considerable N source in agricultural ecosystems (Heichel, 1987; Dakora and Keya, 1997). However, studies on N2 fixation in complex cereal-legume mixtures are few (Stern, 1993; Peoples et al.,, 2002). Intercropping usually includes a legume which fixes N2 that benefits the system, and a cereal component that depends heavily on nitrogen for higher yield (Ofori and Stern, 1986; Cochran and Schlentner, 1995). Controlled studies have shown a significant direct transfer of fixed-N to the associated non-legume species (Eaglesham et al.,, 1981; Giller et al.,, 1991; Frey and Schüepp, 1993; Stern, 1993; Elgersma et al.,, 2000; Høgh-Jensen and Schjoerring, 2000; Chu et al.,, 2004). There was evidence that the mineralisation of decomposing legume roots in the soil can boost N availability to the allied crop (Dubach and Russelle, 1994; Schroth et al.,, 1995; Evans et al.,, 2001). In mixed cultures, where row arrangements and the distance of the legume from the cereal are far, nitrogen transfer could decrease. Research has shown that competition between cereals and legumes for nitrogen may in turn kindle N2 fixation activity in the legumes (Fujita et al.,, 1990; Hardarson and Atkins, 2003). The cereal component effectively drains the soil of N, forcing the legume to fix more N2. Therefore it is important to manipulate and establish how the management practice in legume-cereal mixtures may influence N2 fixation and nutrition in cropping systems.
The microbial biomass is influenced by biological, chemical, and physical properties of the plant-soil system. Generally, soil and plant management practices may have greater impact on the level of soil microbial C (Gupta and Germida, 1988; Dick et al.,, 1994; Dick, 1997; Alvey et al.,, 2003). For instance, soil microbial C tend to show the highest values in cropland and grassland soils and the lowest in bare cultivated soils (Brookes et al.,, 1984; Gupta and Germida, 1988).Monoculture systems are expected to contain less amounts of microbial biomass and activities in comparison to those in mixed cultures (Moore et al.,, 2000). Studies have indicated that legumes accumulated larger amounts of soil microbial C in the soil than cereals (Walker et al.,, 2003). This is attributed to lower C : N ratio of legume than that of cereal (Uriyo et al.,, 1979; Brady, 1990). Microbial biomass activities could increase after the addition of an energy source. The stimulation of soil microbial biomass activity by organic amendments is elevated than that induced by organic fertilisers (Bolton et al.,, 1985; Goyal et al.,, 1993; Höflich et al.,, 2000). Soil organic matter content and soil microbial activities, vital for the nutrient turnover and long term productivity of soil, are enhanced by the balanced application of nutrient and/or organic matter/manure (Bolton et al.,, 1985; Guan, 1989; Goyal et al.,, 1993; Höflich et al.,, 2000; Kanchikerimath and Singh, 2001). Under conditions of adequate nutrient supply such as P2O5, the microbial biomass C will be increased due to improved plant growth and increased turnover of organic matter in the soil (Bolton et al.,, 1985). Whether the management practices in mixed cultures involving legumes and cereals may favour the stimulation of biological soil activity and, thus, result in a higher turnover of organic substrates in the soil that are utilized by micro-organisms is a good subject to be investigated. Although there is a lot of information that show the relationship between soil management and soil microbial activity, little is known about these effects under mixed cropping systems as practised by farmers in the tropical/ subtropical environments (Dick, 1984; Dick et al.,, 1988; Deng and Tabatabai, 1996). In this context, the measurement of their activities could provide useful information concerning soil health, and also serve as a good index of biological status in different crop production systems.
PHOSPHATASE ACTIVITY IN LEGUME/CEREAL MIXTURES
Plants have evolved many morphological and enzymatic adaptations to bear low phosphate availability. This includes transcription activity of acid phosphatases, which tends to increase under P2O5 starvation (Tarafdar and Jungk, 1987; Goldstein, 1992; Duff et al.,, 1994; del Pozo et al.,, 1999; Haran et al.,, 2000; Baldwin et al.,, 2001; Miller et al.,, 2001; Li et al.,, 2002). Phosphatase enzymes in the soil serve several important functions, and are good indicators of soil fertility (Dick and Tabatai, 1992; Eivazi and Tabatabai, 1997; Dick et al.,, 2000). Under conditions of P2O5 deficiency, acid phosphatase secreted from roots is greater than before (Nakas et al.,, 1987; Chrost, 1991;Hayes et al.,, 1999; Li et al.,, 1997). Gilbert et al., (1999) found that white lupin roots from P-deficient plants had significantly superior acid phosphatase activity in both the root extracts and the root exudates than comparable samples from P-sufficient plants. At various starvation levels, these enzymes release phosphate from both cellular (Bariola et al.,, 1994) and extra cellular (Duff et al.,, Ndakidemi 2529 1994) organic compounds. The transcripts and activity of phosphate transporters are increased to optimise uptake and remobilisation of phosphate in P-deficient plants (Muchhal et al.,, 1996; Daram et al.,, 1999; Kai et al.,, 2002; Karthikeyan et al.,, 2002; Mudge et al.,, 2002; Versaw and Harrison, 2002).
It is thought that these morphological and enzymatic responses to P starvation are coordinated by both general stress-related and P-specific signaling systems. The amount of acid phosphatase secreted by plants is genetically controlled, and differs with crop species and varieties (Izaguirre-Mayoral and Carballo, 2002) as well as crop management practices (Patra et al.,, 1990; Staddon et al.,, 1998; Wright and Reddy, 2001). Some studies have shown that the amount of enzymes secreted by legumes were 72 % higher than those from cereals (Yadav and Tarafdar, 2001). Li et al., (2004a) found that, chickpea roots were also able to secrete greater amounts of acid phosphatase than maize. The activity of acid phosphatases is expected to be higher in biologically managed systems because of higher quantity of organic C content found in those systems. In fact, the activity of acid and alkaline phosphatase was found to correlate with organic matter in various studies (Guan, 1989; Jordan and Kremer, 1994; Aon and Colaneri, 2001). It is, therefore, anticipated that management practices in mixed cultures that induce P stress in the rhizosphere, may also affect the secretion of these enzymes. To date, there have been few studies examining the influence of cropping system on the phosphatase activity in the rhizosphere of most legumes and cereals grown in Pakistan. Understanding the dynamics of enzyme activities in these systems is crucial for their assessment their interactions as in turn their activities may regulate nutrient uptake and plant growth in the ecosystem.
EFFECT OF ORGANIC, BIOLOGICAL ANDCHEIMCAL FERTLIZERS ON CROPS AND SOIL
Application of organic manures has various advantages such as increasing soil physical properties, water holding capacity, and organic carbon content apart from supplying good quality of nutrients. The addition of organic sources could increase the yield through improving soil productivity and higher fertilizer use efficiency (Santhi, and Selvakumari, 2000). High and sustained yield could be obtained with judicious and balanced fertilization combined with organic manures (Kang, B.T. and V. Balasubramanian, 1990). Protecting long-term soil fertility by maintaining soil organic matter levels to certain extent, sustaining soil biological activity and careful mechanical intervention, providing crop nutrient directly by using relatively insoluble nutrient sources which are made available to the plants by the action of soil micro-organisms, nitrogen self sufficiency through the biological nitrogen fixation (Hossain et al.,,2004) as well as effective recycling of organic materials including livestock wastes organic manuring (Safdar, 2002).Soil degradation which is brought about by loss of organic matter accompanying continuous cropping becomes aggravated when inorganic fertilizers are applied repeatedly. This is because crop response to applied fertilizer depends on soil organic matter (Agboola and Omueti, 1982).
Among differnret manues poultry manure is highly nutrient enriched organic manure since solid and liquid excreta are excreted simultaneously resulting in no urine loss. In fresh poultry excreta uric acid or urate is the most plentiful nitrogen compound (40-70 % of total N) while urea and ammonium are present in petite amounts (Krogdahl, and Dahlsgard. 1981). Cooperband et al., (2002) assessed phosphorus value of different- age poultry litter composts and raw poultry litter. Available soil P was the highest in plots amended with 15-month old compost, followed by raw poultry litter amended plots. Poultry manure is an excellent organic fertilizer, as it contains high nitrogen, phosphorus, potassium and other essential nutrients. In contrast to mineral fertilizer, it adds organic matter to soil which improves soil structures, nutrient retention, aeration, soil moisture holding capacity, and water infiltration (Deksissa et al.,, 2008). It was also indicated that poultry manure more readily supplies P to plants than other organic manure sources (Garg and Bahla, 2008). As the use of poultry manure becomes an integral part of sustainable agriculture, demand for poultry products increases and pasturelands as well as croplands become nutrient saturated, which has ultimately increased water quality and public health concerns. In addition to high N and P content, raw poultry manure has a potential source of pathogen or E .coli (Jamieson et al.,, 2002; Bustamante et al.,, 2007) and endocrine disruptors (Deksissa et al.,, 2007).
High and sustained crop yield can be obtained with judicious and balanced NPK fertilization combined with organic matter amendment (Kang and Balasubramanian, 1990).The benefits derivable from the use of organic materials have, however, not been fully utilized in the humid tropics partly due to the huge quantities required in order to satisfy the nutritional needs of crops, transportation as well as the handling costs which constitute major constraints. Complementary use of organic manures and mineral fertilizers has been proved to be a sound soil fertility management strategy in many countries of the world (Lombin et al.,, 1991).The need to use renewable forms of energy and reduce costs of fertilizing crops has revived the use of organic fertilizers worldwide. Improvement of environmental conditions and public health important reasons for advocating increased use of organic materials (Seifritz, 1982; Ojeniyi, 2000; Maritus and Vlelc, 2001). Intercropping had no significant effect on cassava root yield but it reduced maize and melon seed yield compared to sole cropping. Land equivalent ratio (LER) values were however higher under intercropping than sole cropping. Crop yields were statistically the same under NPK alone and NPK + poultry manure but significantly higher than both poultry manure alone and control in both locations (Ayoola and Adeniyan 2006).
Satisfactory method of increasing maize yield was by judicious combination of organic wastes and inorganic fertilizers. Titiloye (1982) Nutrient use efficiency might be increased through the combination of manure and mineral fertilizer. ( Murwira and Kirchman (1993).Soil surface remained moist in the intercrop during an unexpected dry spell of 6-8 days when compared to situations under monoculture ofmaize and yam Ghuman and Lal (1987).A system integrating different practices of soil fertility maintenance is required and this will include the use of mineral fertilizer, organic manures and intercropping which provides a fast and good ground cover and also allows the roots to exploit soil nutrients at various depths (Steiner, 1991).Intercropping has been neglected in research on plant production systems in temperate agricultural ecosystems, due to the complexity of these systems and because they are difficult to manage in cropping systems based on agrochemicals. Intercropping can increase organic cereal and grain legume protein production in Europe and will safeguard the organic farmers' earnings and intercropping contributes to a substantial increase of biodiversity in European farming systems.
Competitive organic yields have been obtained in the systems where there is the enhancement of the organic matter and soil biotic diversity occurred (Charles and Shuxin, 2005). An examination of entire agro ecosystem is critical in the development of the successful organic farming system. Short and long term benefits have been described to the organic farming (Delate and Camberdella, 2004). Organic fertilizes including farmyard manure, poultry manure, sheep manure, and bio-fertilizer may be used for crop production as a substitute of chemical fertilizers (Khan et al.,, 2005). Organic fertilizers supply all the essential elements necessary for growth though not in equal proportion, and are readily decomposed by soil microorganisms (Afzal et al.,, 2005). Organic matter produced by organic fertilizers has a strong, positive effect on moisture holding capacity, improvements in aggregation and structure (Sharif et al.,, 2004). Organic fertilizers improve soil fertility without leaving any residual effects in the soil and are much cheaper as compared with chemical fertilizers (Chatter and Gasser, 1970).
A field trial was conducted on deep vertisols of Bhopal, India to evaluate the manural potential of three organic manures: farmyard manure (FYM), poultry manure (PM), phosphocompost (PC) vis-a-vis 0%, 75% and 100% recommended dose of fertilizer-NPK and to find out the most productive cropping system at various combinations of organic manures and chemical fertilizers. The seed yield of intercrop soyabean (population converted to 100%) was 8.7% less than sole soyabean whereas the grain yield of intercrop sorghum was 9.5% more than that of sole sorghum. However, the productivity in terms of soyabean equivalent yield (SEY) was relatively high in intercropping system. The increasing NPK dose from 0% to 100% significantly improved SEY in sole sorghum and soybean/sorghum intercropping system and the integrated use of organics and inorganics recorded significantly more SEY than inorganics. The effect of nutrient management followed the order; 75% NPK+5 t FYM ha-1 > 75% NPK+1.5 t PM ha-1 > 75% NPK+5 t PC ha-1 > 100% NPK. Sorghum, both as sole and intercrop, responded more to PM while soyabean to FYM. Application of 75% NPK in combination with PM or FYM or PC to preceding rainy season crops (soyabean and sorghum) and 75% NPK to wheat produced significantly higher grain yield of wheat than those in inorganics and control indicating noticeable residual effect on the succeeding wheat crop and saving of 25% fertilizer-NPK. The effect of PC on rainy season crops was not as prominent as those of FYM and PM, but its residual effect on grain yield of wheat was comparable to those two organic manures. Among the cropping systems, soyabean as preceding crop recorded the highest seed yield of wheat and was on a par with that of soybean/sorghum intercropping system. The yield of wheat following sorghum was the lowest. The total system productivity (TSP) was the highest in sorghum+soybean-wheat system and the lowest in the soybean-wheat system (Ghosh, P.K; et al.,, 2004).
A field experiment was conducted during 2000 and 2001 in Bhopal, Madhya Pradesh, India, to explore the possibility of increasing oil yield and nutritionally superior quality grains as affected by integrated nutrient management under 3 cropping systems, i.e. soyabean (G. max)-wheat (T. aestivum), sorghum (S. bicolor)-wheat and soyabean-sorghum-wheat. Six nutrient management treatments were applied to each cropping system: 0 (control), 75% recommended NPK, 100% NPK, 75% NPK+farmyard manure (FYM) at 5 tonnes/ha, 75% NPK+ phosphocompost (PC) at 5 tonnes/ha, and 75% NPK+poultry manure (PM) at 1.5 tonnes/ha. Among different combinations of organic and inorganic, application of 75% NPK+5 tonnes FYM/ha recorded the highest protein (34.93%), oil yield (17.87%) and mineral content (4.93%) in soyabean, and the highest protein (9.90%) and mineral (1.66%) contents were obtained in sorghum, both in intercropping as well as in sole cropping, though these were at par with other organically treated plots and 100% NPK-treated plot. Intercropping system as such had no effect on nutritional quality in both soyabean and sorghum. However, wheat grains produced under legume-cereal cropping system (soyabean-wheat) accumulated higher carbohydrates (71.8%), proteins (12.2%), methionine (1.48 g/16g N) and tryptophan (1.37 g/16 gN) compared to grains produced under cereal-cereal cropping system (sorghum-wheat) (Singh et al .2003)
A field experiment was conducted on deep vertisols of Bhopal, India to study the effects of three levels of nitrogen (N), namely 0, 75 and 100% of the recommended dose of nitrogen (RDN), on the dry matter accumulation (DMA) and productivity of three cropping systems (sole soybean, sole sorghum and soybean+sorghum intercropping) during the rainy season and their residual effect on the subsequent wheat crop during the post-rainy season. During the rainy season, sole sorghum was found to have significantly higher DMA and productivity in terms of soybean equivalent yield (SEY) than sole soybean or soybean+sorghum intercropping. Increasing the N dose from 0 to 100% RDN significantly improved the DMA and SEY. At a low fertility level (N0), soybean+sorghum intercropping was found to be more productive, while at a high fertility level (100% RDN), sole sorghum was more productive than the other two cropping systems. However, during the post-rainy season, sole soybean as the preceding crop gave the highest DMA and seed yield of wheat, which were similar to those found with soybean+sorghum intercropping. Sorghum followed by wheat gave the lowest DMA and seed yield of wheat. Application of 100% RDN irrespective of cropping system during the preceding crop improved the DMA of wheat but not its seed yield. However, N applied to the wheat crop significantly increased its DMA and seed yield. (Ramesh et al 2004).
Intercropping had no significant effect on cassava root yield but it reduced maize and melon seed yield compared to sole cropping. Land equivalent ratio (LER) values were however higher under intercropping than sole cropping. Crop yields were statistically the same under NPK alone and NPK + poultry manure but significantly higher than both poultry manure alone and control in both locations Ayoola and Adeniyan (2006). Amanullah et al (2006) conducted field experiments to find out the effect of intercropping and organic manures on the growth and yield of cassava at Veterinary College and Research Institute Farm, Namakkal during 2001 and 2002. The popular hybrid of cassava H 226 was tried as test crop. Three intercropping systems viz., sole cassava, cassava + maize (var. African tall) and cassava + cowpea (var. CO 5) were assigned to main plots. Six organic manurial treatments viz., FYM (25 t ha-1), Poultry manure (10 t ha-1), composted poultry manure (10 t ha-1), FYM (12.5 t ha-1)+poultry manure (5 t ha-1), FYM (12.5 t ha-1)+composted poultry manure (5 t ha-1) along with control (no manure) were assigned to sub plots. The results indicated that intercropping in cassava reduced the growth parameters of cassava in the early stages. But, at later stages this reduction in growth parameters was not significant especially when cowpea was intercropped with cassava. Cassava intercropped with cowpea recorded comparable yield as that of sole cassava. But, there was a significant reduction in tuber yield of cassava due to intercropping of maize. All the organic manures exerted a positive influence on the growth and yield. The best results were obtained in terms of composted poultry manure.
Amanullah et al (2006) conducted field experiments to find out the effect of intercropping and organic manure's on the yield of cassava and the biological efficiency of the cassava intercropping system at Veterinary College and Research Institute Farm, Namakkal during 2001 and 2002. The popular hybrid of cassava H 226 was tried as test crop. Three intercropping systems viz., sole cassava, cassava + maize (var. African tall) and cassava + cowpea(var.CO5) were assigned to main plots. Six organic manurial treatments viz., FYM (25 t ha-1), Poultry manure (10 t ha-1), composted poultry manure (10 t ha1), FYM (12.5 t ha-1) +poultry manure (5 t ha1), FYM(12.5 t ha-1)+composted poultry manure (5 t ha-1) along with control (no organic manure) were assigned to subplots. The study revealed that intercropping in cassava was beneficial in increasing the biological yield, tuber equivalent yield and land use efficiency. Cassava tuber equivalent yield, LER, ATER and AHER was higher in cassava + cowpea combinations. Among the manures, composted poultry manure either alone or with FYM had the highest biological yield, tuber equivalent yield and land use efficiency. The depletion of soil nutrients was lesser in sole cassava followed by cassava intercropped with cowpea.
This study was conducted to assess the possible role of the integrated use of seed inoculation with plant growth promoting rhizobacteria (PGPR), compost and mineral fertilizers for improving growth and yield of wheat sown at different plant spacing. PGPR were isolated from rhizosphere soil of wheat plants. Four treatments were applied in the main plots viz., T1 (Recommended N as Chemical Fertilizer @ 120 kg ha-1 as Control), T2 (Recommended N as Chemical Fertilizer @ 120 kg ha-1 + Compost @ 250 kg ha-1), T3 (Recommended N as Chemical Fertilizer @ 120 kg ha-1 + Compost @ 250 kg ha-1 + Inoculation with PGPR), T4 (Recommended N as Chemical Fertilizer @ 120 kg ha-1 + Inoculation with PGPR). Basal dose of P and K @ 100 and 60 kg ha-1 as Diammonium phosphate and murate of potash respectively was applied to all treatments at sowing time. Maximum increase in plant height, number of tillers m-2, and number of spikelets spike-1, grain and straw yield were recorded with the use of PGPR inoculated seeds in combination with compost and chemical fertilizers. Maximum grain yield and 1000 grain weight were observed where PGPR inoculated seeds were used in combination with recommended chemical fertilizers. Higher N content in grain and straw were recorded with the application of seed inoculation with PGPR along with compost and recommended chemical fertilizers. Planting space had a significanteffect and maximum growth and yield was recorded at 25cm plant to plant spacing. (Akther et al 2009).
Positive effects of organic waste on soil were reported in several studies (Jedidi et al., 2004, Odlare et al., 2007). Several studies (Courtney and Mullen 2007, Gil et al., 2007) suggest that organic sources of P are more effective for plant absorption than inorganic ones. Phosphorus availability from all animal excrements and manures is high (> 70%). Adding of high soluble P quantities brings the soil to saturated stage and a part of the added P remains in the available form and can be leached easily (Kleinman et al., 2000). Odlare M., Pell M., Svensson K. (2007): Changes in soil chemical and microbiological properties during 4 years of application of various organic residues. Waste Manag., doi:10.1016/j.wasman.2007.06.005 A prerequisite to use organic fertilizers in a sustainable way is to quantify the amount of phosphorus and potassium available for plants that could be taken up by a crop. The objective of this study was to evaluate direct and subsequent influence of organic fertilizers addition (poultry manure and two types of composts) on the changes of bioavailability of phosphorus and potassium in soil and their accumulation in the aboveground oat biomass (Avena sativa L.) during three years. The available phosphorus and potassium contents in soil had a degressive trend during the years of experiment. The lowest contents of these elements in soil were found in all treatments in the last year of the experiment. The plants took up the least P and K after application of compost derived from predominant sewage sludge portion. A stronger correlation (R = 0.88; P < 0.05) was found between available content of K insoil treated with organic fertilizers and K content in the aboveground biomass of oat than in the case of P (Hanc,et al., 2008)
Due to the growth in human populations fertilizers were used to increase crop production and meet the rising demands for food. Increases in the production cost, and the hazardous nature of chemical fertilizers for the environment has led to a resurgence of interest in the use of biofertilizers for enhanced environmental sustainability, lower cost production and good crop yields. Plant growth-promoting rhizobacteria (PGPR) are free-living soil-borne bacteriathat colonize the rhizosphere, and when applied to seed or crops enhance the growth of plants (Kloepper 1980). The rhizosphere is the soil found around the root and under the influence of the root. It is a site with complex interactions between the root and associated microorganisms (Sylvia et al., 1998). In the past 10-15 years close to 4,000 publications have appeared in the field of plant growth-promoting bacteria (Bashan and Holguin 1998). Plant growth-promoting rhizobacteria enhance plant growth either by direct or indirect mechanisms (Glick 1995). Plant growth promoting rhizobacteria that have been successful in promoting the growth of crops such as canola, soybean, lentil, pea, wheat and radish have been isolated (Kloepper et al., 1988; Chanway et al., 1989;Glick et al., 1997; Timmusk et al., 1999; Salamone 2000).
(Thavaprakaash et al 2005)Coimbatore during late rabi 2002 (January to March) and late rabi 2002-03 (December to March) seasons to study the impact of varied crop geometry, short duration intercrops and Integrated Nutrient Management practices on production of baby corn based intercropping systems. Two crop geometry levels (45 x 25 cm and 60 x 19 cm) and two short duration intercrops (radish and coriander) along with control (no intercrop) were taken in main plot. Recommended dose of fertilizers (100% NPK-N ) along with three INM practices [50% NPK + FYM 1 + Azospirillum + phosphobacteria (N ), 50% NPK + poultry manure + Azospirillum + phosphobacteria (N ); and 2 3 50% NPK + goat manure + Azospirillum + phosphobacteria (N )] were assigned to sub plot in a split plot 4 design. The trial was replicated thrice. Growth characters such as plant height, LAI and DMP; yield attributes viz., length of cob and corn, diameter of cob and corn and weight of cob and corn; green cob yield and fodder yield were significantly higher at 60 cm wider row spacing than 45 cm spacing level. Whereas, intercrops didn't alter the growth and yield of baby corn. Substitution of 50 per cent NPK through either poultry or goat manures along with Azospirillum and phosphobacteria had significant influence on all the growth and yield parameters and also yield levels of cob and fodder of baby corn. Yield levels of intercrops were higher under closer row geometry (45 cm) than 60 cm spacing. INM practices had less influence on intercrops yield. Whereas, baby cornequivalent yields were higher at 60 cm row spacing, intercropped baby corn with N and N than the rest.The quality of manure, whether it's composted, fresh or aged, has a great impact on the ability to supply nutrients. Long-term application of manures can significantly improve SOM levels. For example, the biannual application of up to 10 t ha-1 of composted poultry manure for 10 years increased SOM by 8.6 t ha-1 (0-30 cm) compared to a conventionally managed system (Horwath et al.,, 2002).
Application of plant growth-promoting rhizobacteria (PGPR) has been reported to increase nodulation and nitrogen fixation of soybean over a range of root zone temperatures (RZTs) under controlled environment conditions. Two field experiments were conducted on two adjacent sites to evaluate the ability of two PGRP strains (Serratia liquefaciens 2-68 or Serratia proteamaculans 1-102) to increase nodulation, nitrogen fixation, and total nitrogen yield by two soybean cultivars under field conditions in a short season area. The results of these experiments indicated that co-inoculation of soybean with B. japonicum and PGPR increased soybean nodulation and hastened the onset of nitrogen fixation early in the soybean growing season, when the soils were still cool. As a result of the increase in these variables, total fixed nitrogen, fixed nitrogen as a percentage of total plant nitrogen, and the nitrogen yield also increased due to PGPR application. Interactions existed between PGPR application and soybean cultivars, suggesting that application of the PGPR to cultivars with higher yield potentials was more effective. Inoculation with PGPR only also increased soybean nodulation and nitrogen fixation by native B.japonicum.
The overall input of nitrogen into global agriculture for food and feed production is estimated to be approximately 120 million tones/ year. Biological nitrogen fixation (BNF) accounts for 40 while 80 million tones/ year is accounted for by N-fertilizer production from ammonia. In cereal production, fertilizer use dominates. If cereals were able to "fix" their own nitrogen the situation could be very different. However, this is unlikely to be realized in the near future unless the technological complexities of inducing BNF in non-legume crops can be overcome. Traditionally, work in this area has tended to focus on the transfer of legume-like BNF characteristics to non-legumes and so far commercially, this strategy has not been successful. More promising may work that has purported to show that some species of endophytic bacteria living within non-legumes (e.g. grasses) can supply nitrogen to their host plants. Many of the current environmental concerns about the use of mineral fertilizers can also be applied to the use of N-inoculants. It was concluded that if N-inoculants for non-legume crops are developed then these will have to be at least as convenient, safe, reliable and effective in growing crops for increasing global population as N-fertilizers are today (Goddard et al., 2003)
Tepary bean (TB), a drought tolerant bean variety has become popular among poor small-scale farmers in semi-arid Kenya, where it is predominantly intercropped with maize. The nitrogen fixation and yield of intercropping tepary bean-maize in comparison to sole crops as affected by nitrogen fertilizer application and inoculation were investigated during two successive growing seasons. Experimental design was randomized complete block with eight treatments: TB sole crop not inoculated with Rhizobium (R3254) and without N fertilizer (N), TB sole crop not inoculated with R 3254 with or without N, TB sole crop inoculated with R3254 without N, TB with maize intercrop not inoculated with R3254 with or without N and maize sole crop with or without N. Each treatment was replicated four times. Significant differences (P#0.05) were observed in total plant dry mass between inoculated and un-inoculated treatments on 21 and 42 days after emergence (DAE). TB yields were significantly reduced in un-inoculated intercrop. Inoculated TB treatments had significantly higher seed dry weights and yields ha-1 compared to un-inoculated. Intercropping TB and maize suppressed the yield of the former under semi-arid conditions. Inoculating TB with Rhizobium strain R3254 was effective and significantly improved TB yields in sole and intercrop. Soil analysis after the two cropping seasons indicated enhancement of soil N in sole TB plots above pre-planting leaves. Maize plots exhibited a decline in soil N. Total N concentration in plant tissues was significantly enhanced in treatment R3254. There was a marked increase in soil P in all treatment plots following amendment. (Shisanya, 2005).
Rhizobia induce the formation on specific legumes of new organs, the root nodules, as a result of an elaborated developmental program involving the two partners. In order to contribute to a more global view of the genetics underlying this plant-microbe symbiosis, a genome sequence for genes potentially relevant to symbiosis was determined. It was expressed that 200 of these genes in a variety of environmental conditions were pertinent to symbiosis. Five new genes induced by luteolin have been identified as well as nine new genes induced in mature nitrogen-fixing bacteroids. A bacterial and a plant symbiotic mutant effective in nodule development have been found that is of particular interest (Ampe et al.,, 2003).
Soils are generally deficient in nutrients, a situation that has negative implications on crop and livestock intensification and hence on food security. The exclusive use of inorganic fertilizers to bring about increased crop production sometimes has negative impact on the soil. On the other hand, the adoption of fallow systems to rejuvenate the soils is becoming even impossible as a result of high population pressures, urbanization and industrialization. Alternative strategies for improving on and sustaining food production are therefore required. Organic manure availability is low since livestock population is low, and intensification without appropriate interventions could even worsen existing soil problems. The adoption of alley cropping is limited by the fact that its practice is restricted to the wetter regions. Modified forms of green manure, which involve the use of food/cash crops that farmers will accept and protect, if needed, are therefore suggested. Pigeon pea (Cajanus cajan L.) is persistent and, if intercropped with other crops, serves as a cover crop that will protect the soil against adverse weather conditions during the dry season (Odion et al.,2007).
In 4 years of field experiments, maize (Zea mays) over yielded by 43 % and faba bean (Vicia faba) over yielded by 26 % when intercropped on a low-phosphorus but high-nitrogen soil. It was found that over yielding of maize was attributable to below-ground interactions between faba bean and maize in another field experiment. Intercropping with faba bean improved maize grain yield and above-ground biomass significantly compared with maize grown with wheat, at lower rates of P fertilizer application (<75 kg of P2O5 per hectare), and non-significantly at high rate of P application (>112.5 kg of P2O5 per hectare). By using permeable and impermeable root barriers maize over yielding resulted from its uptake of phosphorus mobilized by the acidification of the rhizosphere via faba bean root release of organic acids and protons. Faba bean over yielded because its growth season and rooting depth differed from maize. The large increase in yields from intercropping on low-phosphorus soils was especially important on heavily weathered soils. (Lis.Zhang et al.,; 2003).
Plant growth promoting rhizobacteria (PGPR), compost and chemical fertilizers significantly affect the growth and yield of different crops. A novel approach could be that composted material may be converted into a value added product such as an effective biofertlizer by blending with plant growth promoting rhizobacteria which are free living soil bacteria that can either directly or indirectly facilitate rooting (Mayak et al.,, 1999)and growth of plants (Glick, et al.,,1995; Mayak et al.,, 1999). There are several mechanisms by which PGPR affect plant growth such as their ability to produce various compounds (such as phytohormones, organic acids, siderophores), fix atmospheric nitrogen, solubilize phosphate and produce antibiotics that suppress deleterious rhizobacteria, and production of biologically active substances or plant growth regulators (PGRs). Production of biologically active substances or plant growth regulators (PGRs) is one of the major mechanisms through which PGPR influence the plant growth and development (Arshad & Frankenberger, 1998). Therefore the use of PGPR to enhance plant growth and crop yield is predicted to become an emerging trend in contemporary agriculture in the near future (Pal et al.,, 2000).
Most of the legumes are grown in rain-fed areas of marginal lands where indigenous rhizobial population is low in these soils. The result is low yield of legumes as compared with other countries. Low rhizobial population is the main cause of low legume yield in these areas. The use of inoculation is very low; just below 1-3 percent of the total area under legumes which is negligible (Aslam et al.,., 2000). When a legume is introduced in a new locality, it is necessary to inoculate seed with proper rhizobium culture otherwise crop may not thrive and produce nodules. These bacteria although present in most of the soil, vary in number, effectiveness in nodulation and N-fixation. It has been argued that usually native soil rhizobial populations are inadequate and ineffective in biological nitrogen fixation. To ensure optimum rhizobial population in the rhizosphare, seed inoculation of legumes with an efficient rhizobial strain is necessary. This helps to improve nodulation, N fixation, crop growth and yield of leguminous corps (Zamaurd et al.,, 2006).
Symbiotic nitrogen fixing bacteria (SNB) fix nitrogen in association with leguminous plants, are root nodule bacteria. The rhizobium bacteria living in the soil enter the root hairs of the leguminous plants, develop into colonies and form small nodules on the roots. They take their food (carbohydrate) from the leguminous plants and absorb nitrogen from the atmosphere. The legume roots excrete available nitrogenous compound to the soil and enrich it. Rhizobium species invade the root hair of and result in the formation of nodules where free nitrogen is fixed. The amount of nitrogen added to the soil by rhizobium bacteria varies from 50-150 kg ha-1. Biofertilzers (inoculation material) are apparently environmental friendly, low cost, non bulky agricultural inputs which could play a significant role in plant nutrition as a supplementary and complementary factor to mineral nutrition (Sahai, 2004). Rhizobium strains enhance nodulation and the host plant component. It is an attempt to increase nitrogen fixation and the yield at all the sites of harsh climate. Therefore, it is possible to increase nodulation causing improvement in yield from marginal lands by inoculation with rhizobium. (Aslam et al.,, 2001)
Intercropping With Legumes
The intercrop yield advantage and stability, new intercropping designs, the multiple nutrient uses, monitor effects on weeds and diseases, and determine the effects of intercropping on the quality of products for food and feed. Although the potential to limit nitrate leaching through the use of crop mixtures has been widely recognized (Crews and Peoples 2004).In the past monocropping of grain legumes (pulses) was usual practice among the growers but now a days, the interest in growing grain legumes as intercrops with major field crops is increasing. Recent evidence suggests that there are substantial advantages of legumes intercropping which are achieved not by means of costly inputs but by the simple expedient of growing crops together in an appropriate geometry (Nazir et al.,,1997,). When legumes are grown in association with non-legumes, there is often advantage to the non-legumes from nitrogen fixed by the legumes from nitrogen fixed by the legumes (Saeed et al.,, 1997). Intercropping sesame with mungbean in the pattern of 100 cm spaced 4-row strips appeared to be more convenient, productive and profitable than the monocropped sesame.
Intercropping and succeeding crop
Preceding effect studies of grain legumes have largely focussed on soil N changes (Jensen E.S., and H. Hauggaard-Nielsen 2003)., but questions and methodological difficulties still remain concerning the contribution of the below ground part of the legume and the quantification of N2O emission (M.B. Peoples 2001). Variation in non- N characteristics (pathogen inoculum size, weed seed bank, microbial activity.) are difficult to study directly and are mainly approached through the sensitivity of the following crop (Stevenson and Kessel 1996). This latter concept is relevant for two reasons. On the one hand, the preceding effect of the grain legume (crop n) will largely depend on its sensitivity to the preceding effect of crop n-1. As an example, N2 fixation of pea is very sensitive to soil inorganic N left at sowing by the preceding crop and/or it can be affected by soil compaction or weed stock enhanced by a preceding crop ( Crozat ,2000 ). Secondly, expression of the preceding effect of the grain legume (crop n) depends on the characteristics of the following crop n+1 (for example, date of sowing, nutriments uptake ability). Moreover, in order to take into account climate-crop management interactions, further studies on the cumulative effects (long term repetition of the rotation) should be undertaken in order to better assess the role of grain legumes in crop rotation.
Introducing a grain legume into a crop succession not only contributes to the production of materials rich in protein (ecological function of producing food and raw materials) but also modifies properties of the whole cropping system such as N cycling, regulation of pests and diseases, soil physical and biochemical fertility (Yves. 2004)
The grain legumes have important functions in the crop rotation via their nitrogen and non nitrogen benefits for succeeding crops. In a grain legume-cereal sequence the nitrogen benefits are related to nitrogen carry-over of unused inorganic N and crop residue N from the grain legume phase, which can reduce the need for nitrogen, supply in the subsequent crop and potentially contribute to soil fertility building. The significance of the N benefits in the short and long terms in a cropping system is determined by the crop N balance, the soil N dynamics post after the crop has stopped to take up N from soil and the nitrogen demand of the succeeding crop. The non-nitrogen benefits, some of which are referred to, as the "break-crop effect" are numerous. These are reduced root and leaf diseases in subsequent crops, reduced weed population, increased P, K and S availability, ameliorated soil structure, release of growth substances from legume residues, increased soil organic matter and increased mi