Maize rhizosphere soil stimulates greater soil microbial biomass and enzyme activity leading to subsequent enhancement of cowpea growth

  • Ricardo Silva de Sousa
  • Luis Alfredo Pinheiro Leal Nunes
  • Jadson Emanuel Lopes Antunes
  • Ademir Sérgio Ferreira de AraujoEmail author
Short Communication


Rhizosphere from different plant species can influence differently the soil microbial biomass and activity. The aim of this study was to evaluate the effect of rhizosphere of maize and cowpea on soil microbial biomass and enzymes. Soil samples adhered to the roots of maize were collected at 45 (flowering) and 75 (senescence) days; while for cowpea, soil samples were collected at 35 (flowering) and 60 (senescence) days. Soil microbial biomass C was highest in soils from the rhizosphere of maize. The activity of dehydrogenase and β-glycosidase were highest in soils from the rhizosphere of maize, while phosphatase was higher in soils from the rhizosphere of cowpea. This study concluded that soils from rhizosphere of maize presented higher soil microbial biomass and enzyme activity in comparison to soils from rhizosphere of cowpea.


Microbial properties Roots Legumes Gramineae Rhizosphere 


Rhizosphere is a specific zone surrounded by the roots that influence, due to their exudates, the activity of soil microorganisms (Qiao et al. 2017). This zone presents high amount of C released through rhizodeposition (Zang et al. 2015) and these C sources strongly influence the soil microorganisms living in the rhizosphere (Jacoby et al. 2017). Also, the quality and quantity of these root exudates can vary according to the plant species and development (Jones 1998). Thus, this variation in plant species and their rhizosphere and exudation could influence differently the soil microbial biomass (SMB) and activity (Wang et al. 2017).

SMB represents the highest fraction of soil biodiversity and acts on several soil functions that are important for the environmental sustainability, such as the dynamic of organic matter and nutrient cycling (Li et al. 2018). Also, SMB releases some enzymes that act on the biogeochemical cycles and contribute with nutrients for plants and the microbial activity (Ren et al. 2018). Thus, the evaluation of the status of SMB and soil enzymes becomes important for the understanding of the influence of different plants rhizosphere on soil microbial properties. Previous studies about rhizospheric effect on soil microorganisms have shown that different plant species drive differently the microbial biomass and activity (Chaudhary et al. 2012; Gardner et al. 2011; van Wyk et al. 2017). Changes in root growth and activity following the plant vegetative development, such as flowering and senescence, can also influence the soil microbial biomass and activity (Mukherjee and Kumar 2007). Therefore, in this study we hypothesized that (1) maize and cowpea present different rhizosphere traits and would affect the size of microbial biomass and activity; (2) the soil microbial biomass and activity could be different during the flowering and senescence. Usually, the studies have evaluated the crop rotation with Gramineae after legume aiming to verify the effect of legumes, mainly N fixation, on maize growth. In contrast, this study evaluated the effect of the rhizosphere of maize and cowpea during the flowering and senescence on soil microbial biomass and activity.

Material and methods

The study was conducted at the Experimental Field of the Agricultural Science Center, Federal University of Piauí, Teresina, PI, Brazil (05°02′ latitude S e 42°47′ de longitude W). The mean of temperature is 25 °C and the soil of the area is classified as a Fluvisol (10% clay, 28% silt, and 62% sand). The experiment was designed in a completely randomized design with four replicates. The experimental plots presented 20 m2 each one, being 12 m2 the usable area for soil sampling. The sowing was done in December, 2016 (during the summer). Maize (Zea mays L.), AG 1051, was sowed at a density of five plants m−1 (approximately 62,000 plants ha−1) and grew for 75 days. Afterward, cowpea (Vigna unguiculata L.), BRS Tumucumaque, was sowed at the density of six plants m−1 (approximately 120,000 plants ha−1) and grew for 68 days. The soil was fertilized only in the beginning of experiment, before maize sowing, with NPK at 20–100–80 kg ha−1 (N-urea; P-super single phosphate; K-potassium chloride). After 30 days of maize emergence, the soil was supplemented with 100 kg ha−1 N. For cowpea crop, the soil was not fertilized. The plants were grown under rainfed conditions.

In order to measure the rhizospheric effect on soil microbial properties, four plant per plot were sampled and the soil adhered to the roots were collected and mixed to form a composite sample per plot. For maize, the sampling was done at 45 (flowering) and 75 (senescence) days; while for cowpea the sampling were at 35 (flowering) and 60 (senescence) days. The roots of plants were separated, dried at 65 °C until constant weight, and weighed. Maize and cowpea yield were evaluated by sampling ten plants from inside the plots, and grains were dried for 13% of humidity.

The soil samples were sieved (2-mm), and stored at 4 °C prior to analysis. Soil chemical properties are shown in Table 1. Soil pH, exchangeable Ca2+, Mg2+, K+, and the available P were estimated according to Embrapa (1997). Soil microbial biomass C (MBC) was estimated by the microwave irradiation extraction method (Islam and Weil 1998). An extraction efficiency coefficient of 0.21 was used to convert the difference in soluble C between irradiated and non-irradiated soils in MBC. TOC was determined by wet combustion using a mixture of 5 mL of 0.167 mol L−1 potassium dichromate and 7.5 mL of concentrated sulfuric acid under heating (170 °C for 30 min) (Yeomans and Bremner 1988). Soil basal respiration (BR) was measured by CO2 released under aerobic incubation at 25 °C for 7 days (Alef and Nannipieri 1995). The microbial quotient (qMic) was calculated as the ratio of MBC to total organic carbon (TOC), expressed as percentage (%). Dehydrogenase (DHA) activity was determined according to Casida et al. (1965), based on the spectrophotometric analysis of triphenyl tetrazolium formazan released by 5 g of soil after 24 h of incubation at 35 °C. Phosphatase (PHO) activity involved the colorimetric estimation of the p-nitrophenol released after 1 h of incubation at 37 °C (Tabatabai and Bremner 1969). β-Glucosidase (GLY) activity was measured according to the method described by Eivazi and Tabatabai (1988).
Table 1

Soil chemical properties










g kg−1

mg kg−1

cmolc kg−1

cmolc kg−1

cmolc kg−1




































Letras minúsculas seguidas na mesma coluna diferem estatisticamente pelo teste de Tukey (p < 0.01)

TOC total organic C, NP no plants, MF maize flowering, MS maize senescence, CF cowpea flowering, CS cowpea senescence

Microbiological data were evaluated with univariate statistical analysis (ANOVA), considering sampling time, through R software (R Core Team 2016). Redundancy analysis (RDA) was used to visualize the differences between the treatments and determine its correlation with the microbial variables. Monte Carlo permutation test were applied with 1000 random permutations to verify the significance of treatments upon the microbial variables. RDA plots were generated using Canoco 4.5 software (Bio-metrics, Wageningen, The Netherlands).

Results and discussion

Soil basal respiration did not show significant differences between treatments (Fig. 1a), while MBC was highest in soils from the rhizosphere of maize in comparison to cowpea, in both flowering and senescence period (Fig. 1b). Soils from rhizosphere of maize presented about 20% more content of MBC than soil from rhizosphere of cowpea. The lowest MBC was found in the treatment without plants. The microbial quotient did not vary between soil samples from the rhizosphere of both plants while it was lowest in the treatment without plants (Fig. 1c). The values of microbial quotient were higher than 2% in soil from rhizosphere of maize and cowpea. The activity of dehydrogenase and β-glycosidase were highest in soils from the rhizosphere of maize (Fig. 2b) showing an increase of 50% and 300% in dehydrogenase and β-glycosidase, respectively, in the rhizosphere of maize as compared with cowpea. In contrast, the activity of phosphatase was highest in soils from the rhizosphere of cowpea than in maize (Fig. 2b). RDA explained 20.6% of the total variation of which 26.8% is displayed on the horizontal axis and another 52.7% on the vertical one (Fig. 3). The results showed cowpea separated from maize in both flowering and senescence periods. Also, the variables GLY, qMic, and MBC were clustered with the plant species during the flowering, while DHA, PHO and BR clustered with plants species during the senescence.
Fig. 1

Basal respiration (a), microbial biomass C (b) and microbial quotient (c) in soils from rhizosphere of maize and cowpea. NP no plants; MF maize flowering; MS maize senescence; CF cowpea flowering; CS cowpea senescence

Fig. 2

Activities of dehydrogenase (a), glucosidase (b), and phosphatase (c) in soils from rhizosphere of maize and cowpea. NP no plants; MF maize flowering; MS maize senescence; CF cowpea flowering; CS cowpea senescence

Fig. 3

Redundancy analysis diagram (RDA) of correlations between microbial properties and treatments. The variables treatment and sampling date were introduced as supplementary environmental variables. Treatments NP no plants; MF maize flowering; MS maize senescence; CF cowpea flowering; CS cowpea senescence. Microbial properties DHA dehydrogenase; PHO phosphatase; BR basal respiration; MBC microbial biomass C; qMic microbial quotient; GLY glucosidase

In line with hypothesis (1), different plant species had significant rhizospheric effect on soil microbial properties. In general, microbial properties presented highest values in the rhizosphere of maize than cowpea. In contrast with hypothesis (2), for both plants, the period of flowering or senescence did not influence the soil microbial properties.

Soil microbial biomass and qMic showed the highest values in rhizosphere than in bulk soil. Soil from rhizosphere often presents larger microbial biomass than bulk soil (Guo et al. 2015). This difference occurs due to the exudates released from plant roots that supply C sources for soil microbial biomass (Steinauer et al. 2016). However, SMB was highest in rhizosphere of maize than in cowpea. There are two possible reasons: (a) maize presented highest root biomass than cowpea and it could have contributed for increasing MBC in maize rhizosphere. Indeed, we found that maize produced more root biomass than cowpea. The values of root dry weight of maize were 2.16 g pl−1 (flowering) and 4.60 g pl−1 (senescence); while cowpea presented the values of 0.31 g pl−1 (flowering) and 1.02 g pl−1 (senescence); (b) The rhizosphere of different crop species can exudate different organic compounds. The variation of organic compounds released by roots has been suggested to be the main driver of the response of microorganisms in the rhizosphere of different plant species (Bolton et al. 1992). Usually, rhizosphere of species belonging to Gramineae, such as maize, can release more carbohydrates content than legumes (Fageria and Moreira 2011) and it may have favored the MBC in maize rhizosphere. In contrast, cowpea presents the ability for changing soil pH in the rhizosphere (Makoi et al. 2010) and it could affect the SMB. According to Rao et al. (2002), cowpea roots release high amounts of organic anions that contribute for decreasing soil pH. Thus, these factors could have contributed for different responses of soil microbial properties in the rhizosphere of both plants.

The highest activity of dehydrogenase and β-glycosidase found in soils from rhizosphere of maize can be related by the induction of catabolic enzymes by the exudates released from maize roots (Vilchez et al. 2000). There is no information about the induction of these microbial enzymes in rhizosphere of cowpea. These results agree with Neogi et al. (2014) who reported highest dehydrogenase and β-glucosidase activity in soil cultivated with maize than by cowpea. On the other hand, the highest phosphatase activity found in the rhizosphere of cowpea can be associated with the facilitation of P availability by the maize that was cropped before cowpea (Li et al. 2004). One possible reason for this higher P availability would be the changes in soil pH in rhizosphere promoted by cowpea (Rao et al. 2002) that contribute for increasing nutrient availability in its rhizosphere by 45–120% (Dakora et al. 2000). Previous studies have also found higher phosphatase activity in soil cropped with legumes than Gramineae (Lyu et al. 2016; Png et al. 2017). The activity of phosphatase differs according with the plant species (Cabugao et al. 2017) and usually this enzyme increases about 70% in rhizosphere of legumes than Gramineae (Li et al. 2004).

RDA clearly separated the treatments according to the microbial variables and showed differences between plants species and stage of development. This finding shows that the stage of development influences the responses of microbial properties. Thus, GLY, qMic, and MBC were influenced by the high rhizosphere activity and increased their values. On the other hand, DHA, PHO and BR presented correlation with the plant senescence due to the presence of high mass of roots.

The findings found in this study are important for selecting crops to be used in sustainable agriculture as stimulator of microbial biomass and enzymes. The increase in SMB by using maize could be a strategy for improving the environmental sustainability since higher microbial biomass means environmental stability (Araujo et al. 2013), storage of nutrients, plant productivity and stimulation of beneficial plant–microbe symbioses (Kaschuk et al. 2010). Similarly, some studies have found significant correlation among soil enzymes and sustainable yield index of plants (Lopes et al. 2013; Gong et al. 2016). In addition, the highest microbial biomass and enzymes activity promoted a suitable cowpea yield without fertilization. In this study, maize and cowpea yielded 4.65 and 1.34 ton ha−1, respectively, and it suggests positive effect of maize planting before cowpea. Indeed, the cowpea yield was similar to those observed by Xavier et al. (2008) that ranged from 0.53 to 1.45 ton ha−1 by using different doses of chemical fertilizers. Finally, this study showed that soil from rhizosphere of maize stimulated the increasing of SMB and enzyme activity and it contributed to subsequent improvement of cowpea growth.


This study showed that different plant species influence differently the soil microbial properties. Thus, soils from rhizosphere of maize presented usually higher SMB and enzyme activity than soils from rhizosphere of cowpea. The highest SMB and enzymes may have contributed to maintain cowpea yield without fertilizers. Therefore, the maize plantation could be a good strategy for enhancing the soil quality before cowpea plantation.



Ademir S. F. Araujo thanks to Conselho Nacional de Desenvolvimento Científico e Tecnológico – CNPq/Brazil (grant 305102/2014–1) for its fellowship of productivity.


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Copyright information

© Society for Environmental Sustainability 2019

Authors and Affiliations

  • Ricardo Silva de Sousa
    • 1
  • Luis Alfredo Pinheiro Leal Nunes
    • 1
  • Jadson Emanuel Lopes Antunes
    • 1
  • Ademir Sérgio Ferreira de Araujo
    • 1
    Email author
  1. 1.Soil Quality Laboratory, Agricultural Science CenterFederal University of PiauíTeresinaBrazil

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