Intercropping Induce Changes in Above and Below Ground Plant Compartments in Mixed Cropping System

Crops growing in a mixture is an ancient agricultural practice and usually been used for improving yield and growth of the crops and to fulfill the world fast growing population food demand. The two crops growing on same soil zone may be in direct competition to utilize the available resources because planting plants on same land using the same resources for normal growth. In intercropping system there may be facilitative and competitive interaction among the plants in both above and below ground plants compartments. The intension of intercropping is to utilize the use of physical, temporal and spatial resources both above and below ground plant compartments by maximizing the complementary interaction and minimizing the competitive ones. The changes and complex interaction both in upper and underground plant parts in inter-cropping system those adopted by local farmers in China are not yet fully understood. Information’s from such studies are likely to provide knowledge about the complex interactions among two crops growing in a mixture. This study was therefore assessed to perceive how plants in mixture change the above below ground compartments and how they interact.


Introduction
Intercropping is an old cropping system which dates back to ancient civilization and practice globally to achieve more yields and to satisfy the world food demand [1][2][3][4][5][6]. Mix cropping system not only enhance crop production and returns but can help safe the plants from complete failure as compare to mono-cropping [2].
The purpose of intercropping is to efficiently utilize the available plant growth resources like water [3], nutrients [4], and sun light and to minimize the competition and control weeds, disease and pest incidences [5]. The facilitations occurs both above and below ground plant compartments when plants using the same soil zone [7,8]. Cereal-legumes intercropping is common cropping system in which cereal get growth and yield advantages from legumes by sharing nutrients and some other unknown resources [1,9]. It is well known that plants growing in mixture interact with each both positively and negatively in the above and below ground plant compartments. The above plants facilitative integrations are well investigated, however what's going inside in the below ground plants-soil and plant-plant in mix cropping system are still not clear [9][10][11]. Rhizospheric plant roots, soil and microbial interactions are beneficial to plant ecosystem. Rhizosphere root exudations process play a vital role in plant nutrition [12,13].
To date, the below ground interactions in intercropping and its effect on plant growth acquired a little attention [9][10][11]. To achieve greater yield, improve rhizospheric microbial conditions, soil quality betterment, resources utilization, soil nutrients recycling, proper management practices require in mixed cultures [14]. Though cereals and legumes grown singly are highly investigated but few researches are available on the complex mixed cropping system specially on the below ground plant compartments (rizhosphere interactions), hence more studies are require explore the fact about rhizospheric soil in intercropping [9]. The intension of growing plants in a mixture is to efficiently utilize facilitative (positive interactions) resources and curtail competitions both in the above and underground plant compartments [15][16][17][18][19][20][21][22]. insufficient literatures are available on the on the below ground mechanism involved in mix cropping system those practice by traditional farmers [9,11] because it's complexity in mixed cropping system rhizosphere. This study is therefore design to collect information for understanding above and below ground interaction in crop mixtures ( Figure 1).

Rhizospheric interaction in intercropping
In intercropping system both plant species uses the same soil zone for root resources which directly associated with growth per-

N 2 fixation, N Uptake and N Transfer in Cereal/Legumes Intercropping
Nitrogen is key element required for plants normal growth and productivity. More research are available on the biological N fixation in grain legumes [35, [68][69][70] because of legumes are able to acquire almost 75 % of their nitrogen requirement from atmosphere [71,72]. Nevertheless, less study on the biological nitrogen fixation in cereal/legumes mixture are available [70,73]. More specifically, the cropping mixture typically exhibits nutrients advantage [74,75]. Nitrogen uptake in mix cropping system enhances the nutrients status of associated crops. This N facilitation in intercropping system may be due to that, leguminous crops obtain N through biological nitrogen fixation which then available or transfer to associated cereal crop by direct root contact or exudation and mycorrhizal association and thus improve the N 2 fixation ability of legumes [76]. it is well know that intercropping cereal with legumes under low fertilization improve the N nutrient in cereal and thus overyield [50].
Previously documented that different cropping system like wheat/soybean, maize/faba bean, barley/pea and sorghum/ soybean significantly increased the N acquisition compare to sole cropping system [77][78][79]. The atmospheric N taken up by faba bean was increased 8% to33% (early flowering stage), 54%-61% (full flowering stage),18%-50% (grain-filling stage), and up to 72% (full maturity stage) than monocropped faba bean [80]. The 15 N labeling techniques are using for direct transfer of N from legumes to neighboring non-legume plant in intercropping system, legumes are the dominant crop for fixing atmospheric nitrogen which is beneficial to the system [20,81], increase the N uptake in cereal and thus yield. It is evident previously that nitrogen fixed by legumes can be significantly transferred to their associated non-legumes crop grown in a mixture [68,69,73,82,83]. Thereby increased the soil N content [36, 84,85]. In mixed culture, planting legumes at long distance from non-legumes may lead to decreasing N transfer.
In past researcher declared that N competition in legumes/cereal mixed culture may further be increase through nitrogen fixing activity by leguminous crops [79,86]. Cereal plants efficiently utilize soil N which results more N fixation in legumes. It is therefore an important study to expose the effect of planting mixtures on biological nitrogen fixation and nutrition.

Soil Microbial Biomass in Intercropping
Microbial biomass in plants mixture is influence by various physio-chemical and biological characteristics those involve in an intercropping system. In general, soil microbial C is highly affected by different agricultural practices [87][88][89]. For example, the farm-land and grass land found to be higher in soil microbial C than uncultivated lands [87,90]. Intercropping in comparison with single cropping is expected more suitable cropping pattern for increasing soil microbial biomass. The intercropping of durum wheat with legumes like chickpea, lentil increased the soil microbial biomass [91]. Studies on the legumes has shown that these plants are capable to increase soil microbial C than cereal [92], tend to reduce carbon to nitrogen ratio in legumes compare to cereals. The microbial biomass activities can further be increase by adding any energy sources to soil. Higher microbial biomass activities can be expected in soil by natural manuring than commercial fertilization [93,94]. Soil microbial biomass activity and organic matter are responsible factors for improving soil nutrients status, fertility and productiveness and can be enhanced by additional organic sources incorporated to the soil [93,94]. Under sufficient application of P, the soil microbial biomass can be boost in a result plant growth and soil organic matter can also be improve [93]. The biological soil activity in legumes/cereal mixture results in improving soil organic substrates utilizing by soil micro flora need more research attention. Although soil-microbes relationship has been considerable investigated but few literature are available on such studies those practice in humid regions [95]. In this prospective, useful information can acquire by measuring these activities in a relation to soil health in diverse cropping system.

Phosphatase Activity, P Acquisition and P Uptake in Intercropping
Intercropping can improve the P uptake under P deficient soil immobilize P and benefit the non-P moblizing crops in mix cropping culture [98]. In P-impoverished soil, some species form dauciform roots or cluster roots [98]. It reviewed earlier that Dauciform roots or cluster roots exude carboxylates and mobilize soluble P in soil increased P acquisition and supply P to neighbor plant in inter-crop [99]. Numerous studies have shown P use efficiency in Phosphatese enzyme is a key factor involving in soil fertility and performs different functions [110][111][112]. This enzyme is more likely to increase in low P soils [59, [113][114][115][116], a comparative research on the acid phosphotase activity in white lupin root growing in high and low phosphorus soils show that acid phosphotase activity both in root extracts and root exudates in low P soil were significantly higher. Under different stress level these phosphatase enzyme are able to releae phosphate from cells [104,117]. The increasing rate of P transportation in P-deficient plant is because to remobilize and optimize P uptake [118][119][120][121][122][123][124][125][126][127][128][129][130]. These enzymatic and completion of P starvation are considered to be managed by common P stressrelated and specific signaling system.
The secreted plant acid phosphate amount is genetically controlled; differ at plant to plant [124] and various cropping techniques [126][127]. Different experimental results showed that legumes plants discharge more enzymes compare to grain crop as for instance [128] in their experiment observed that the enzyme secretion by legumes was 72% higher than that of cereals.
The amount of enzyme secrete by chickpea root was higher than maize plant [62]. In biological manage system phosphate activity expected to be higher because of high carbon present in the system.
As these activity of was found to be correlated with OM in different studies [129,130]. Hence mix cropping practices is expected to