Research PaperBiological attributes of soil cultivated with corn intercropped with Urochloa brizantha in different plant arrangements with and without herbicide application
Introduction
The economic success of intercropping systems between corn and forage depends on the planting density adjustment and on reducing the initial forage growth. The forage growth can be retarded by application of sub-doses of herbicide such as nicosulfuron (Freitas et al., 2015, Pariz et al., 2017).
However, practices adopted in intercropping systems can change the soil microbial activity, affecting nutrient cycling, decomposition of organic matter and the physical and chemical proprieties of the soil. Thus, microbiological indicators are used to evaluate disturbances in the ecosystem (Totola and Chaer, 2002; Bottomley, 2005).
Among the microbiological indicators, respiratory rate (RR), microbial biomass carbon (MBC), metabolic quotient (qCO2), glomalin production, mycorrhizal colonization, and the number and diversity of spores of mycorrhizal fungi are frequently used (dos Santos et al., 2005, Aguilera et al., 2014, Rillig et al., 2002, García-González et al., 2016, Meddad-Hamza et al., 2017).
Respiratory rate measures the CO2 production resulting from the metabolic activity of macro and microorganisms in the soil (Karhu et al., 2014a, Karhu et al., 2014b). The MBC is the living part of the soil organic matter involved in the degradation of organic matter, nutrient cycling and the degradation of toxic compounds in soil (Getahun et al., 2016; Moormam, 1994).
The qCO2 is the relationship between the respiratory rate per microbial biomass carbon (CBM) and is considered the most appropriate indicator in the short term to evaluate the effect of management practices on soil microbial activity (Xue et al., 2017)
The diversity of arbuscular mycorrhizal fungi (AMF) depends on the stability of plant communities and the soil management (Bouffaud et al., 2017, Jansa et al., 2014). AMF are obligatory symbionts able to associate with approximately 80% of plant species. This combination increases the ability of nutrient uptake by plants, increasing the competitiveness and productivity of crops.
The aim of this study was to evaluate the effects of sowing different densities of Urochloa brizantha intercropped with corn with and without spraying of nicosulfuron on microbiological indicators of soil quality.
Section snippets
Materials and methods
The experiment was conducted under field conditions in a completely randomized design at the Experimental Station Teacher Clibas Vieira, belonging to the campus of the Federal University of Viçosa, Viçosa-MG. The soil was classified as Ultisol (Table 1).
Fertilization was performed according to soil analysis and in accordance with recommendations for corn. Fertilizer 4 – 14 – 8 (NPK) at 400 kg ha−1 was applied in the planting line of corn. Extra fertilization of 120 kg N as urea was performed 20 days
Results and discussion
Increased Urochloa brizantha density elevated the carbon associated with the MBC with and without nicosulfuron application (Fig. 1).
The nicosulfuron application at 8 kg ha−1 of i.a. did not reduce the population of microorganisms in the red-yellow podzolic, whereas microbial biomass in these plots was not lower than in plots without application of nicosulfuron. The absence of negative effects of the herbicide on some microorganisms present in soil shows its ability to metabolize the nicosulfuron
Conclusion
Increasing Urochloa brizantha sowing densities up to 6 kg ha−1 negatively interferes with the evolution of CO2, percentage of mycorrhizal colonization and total number of spores. However, microbial biomass carbon (MBC) and the metabolic quotient (qCO2) were positively affected by increasing the Urochloa brizantha density, indicating that corn-signalgrass intercropping provided favorable conditions for the growth of soil microbial populations. Microbiological soil properties and corn yield were
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