Increase in Symbiosis Efficiency for Intercropped Legumes with Cereals

Recent research studies on legume-cereal intercropping system have shown the efficient use of environmental resources by stimulating plant growth and yield in low-input soils (Cong et al., 2015; Latati et al., 2016), compared with fallow-cereal rotation practice. The legumes could increase the availability of nutrients such as N (Betencourt et al., 2012) and P (Latati et al., 2014) in the rhizosphere of the intercropped cereals, improving grain yield, nutrient uptake and efficiency in use of rhizobial symbiosis (EUR), especially in low P conditions (Houassine et al., 2019). Intercropping can also improve growth and nutrient use efficiency through the stimulation of biological N, fixation by nodules of the intercropped legumes (Bargaz et al., 2012) (Figure 1.1). Latati et al. (2017) confirm that N uptake in legumecereal intercropping is greater as a result of a higher EURS under low soil input (e.g., P and N). Xu et al. (2013) reported that the changes in the C:N ratio of soil microorganisms (fungi and bacteria) have also been attributed to the relative demand of soil microbes for C and N. These changes may have a major effect on N and C cycling.

Previous literature on intercropping have shown that little information is available on the effects of cereallegume intercropping on microbial mediated processes and the relation between intercropping and biological

Nodules dry weight (g plant4)

FIGURE 1.1 Efficiency in the use of rhizobial symbiosis of chickpea as sole crop (A and C) and intercrops (B and D) in 2015 and 2016. The equations inserted in the graphs are the regression functions. “** and ***” denote significance at p < 0.01 and p < 0.001. respectively. (Latati et al., 2020)

N, fixation by the intercropped legumes. Microbial biomass (MB) and EURS are considered as strong biological indicators for monitoring agroecosystem changes in rhizosphere of intercropped legume (cowpea, common bean, and chickpea) with cereals (maize and durum wheat). It is also considered as important for planning appropriate land use and for the management of agriculture practices (Latati et al., 2016, 2019).

Use and Application of MOMOS Model in Intercropping Agroecosystem

The MOMOS model (soil microorganism and organic matter model) is one of the most mechanistic models, which was developed and improved recently to simulate the daily exchanges of both C and N cycles within the soil-plant-microorganisms system. The MOMOS model was first developed and validated in such a way as to focus on crop system parameters that were studied under controlled conditions (e.g., incubation experiments) with the use of isotopic tracing (Pansu et al., 2004). No application on an open complex agroecosystem with regular flows of field conditions has yet been published except for Ibrahim et al. (2013, 2016), Pansu et al. (2018), and Latati et al. (2019). Indeed. MOMOS model parameters are strongly related to both soil moisture and temperature to better study the agroecosystem’s sustainability and resilience in the face of climate change.

Role of the MOMOS Model in the Characterization of C and N Dynamics in Agroecological Systems

According to the MOMOS validation at agroecosystem scales, a recent research study demonstrated the possibility of predicting the daily interactions of CN stocks between the different organs of the plant (e.g., shoot, root, and nodules), soil, and atmosphere by simulating the functional role of microorganisms,

Carbon and nitrogen stocks in shoot of intercropped maize and common bean

FIGURE 1.2 Carbon and nitrogen stocks in shoot of intercropped maize and common bean.

in particular N,-fixing rhizobial bacteria. The MOMOS model contributes to the assessment of microbial activities via labile and stable OM assimilation (Humus and necromass) as well as root exudates with a simulation of C and N fluxes between all compartments of complex system soil-plant-microorganism (Thornton et al.. 2004; Pansu et al., 2018; Latati et al.. 2019).

The different simulations relative to daily exchange of C and N stocks in shoots of both intercropped common bean and maize (Figure 1.2) show significant adjustment between measured and simulated data. Recent research studies reported that the MOMOS model appears as a strong tool for assessment and analysis of various ecophysiological parameters, and to predict correctly an important data in the case of biogeochemical cycles studies (Ibrahim et al., 2013).

Microbial Biomass in the Rhizosphere of Intercropped Legumes

The MOMOS model was also used to simulate soil MB activities during crop cycle of either a maizecommon bean (Latati et al., 2019) or wheat-faba bean (Ibrahim et al., 2016; Pansu et al., 2018) intercropping system. MB is characterized by rapid turnover compared to other OM compartments (e.g., necromass, residues, humus stable) and in particular as compared to the total C and N in the soil (Butler et al., 2004; Pansu et al.. 2010).

MB is considered as a key indicator to assess agricultural practices’ sustainability in an agroecosystem (Sparling et al., 1998; Barthes et al., 2008). The daily simulation of the MB-C and MB-N exchanges of microbial biomass in the rhizosphere of intercropped legumes-cereals (Figure 1.3) revealed the role of soil microorganisms in stimulating and controlling CN transfers in these intercropped species grown in a mixture crop. However, the C stocks in MB increase simultaneously with the increase in N-MB from the sowing to harvest time of the crop cycle (Molina and Smith, 1998; Cong et al., 2015), the high rate of this increase was systematically observed during full flowering stage of intercropped legumes (Figure 1.3).

Latati et al. (2017) reported a significant relation between biological N, fixation and the microbial biomass activity in the rhizosphere of common bean grown intercropped with maize. These authors confirm

Day after sowing

FIGURE 1.3 The simulation of carbon and nitrogen in rhizosphere microbial biomass of both intercropped maize and common bean.

that the C and N may also be transferred from the nodules of intercropped legume to the rhizosphere where they were assimilated by the microorganisms during their growth stage. This constitutes an important N and C stock in the rhizosphere MB for intercropped cereals.

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