**5. Soil management for enhanced maize production**

Severely disturbed land is a global concern because changes in land use are one of the biggest threats to biodiversity and ecosystem services worldwide. This is exacerbated by increased demand for agricultural production. Studies conducted have shown that disturbance not only reduces AM fungal abundance, diversity and infectivity but can also result in drastic shifts in the AM fungal community [156]. AM fungal hyphae and root litter are the most abundant carbon source in the soil [157], providing energy for other soil microbes to flourish [92]. They may increase the diversity and abundance of microorganisms beneficial to plant growth and health [157]. Hyphae are highly susceptible to disturbance and disturbance results in reduced infective potential of AM fungi [157]. As the scale of degradation increases, the abundance and diversity of AM fungi reduces [158].

Tillage management plays a central role in ecological and biological stability, which is closely related to soil quality, by influencing the activities of soil microbial communities [159–161]. Soil disturbance, caused by tillage or plowing, decrease AM fungal colonization, disrupt AM hyphal networks [162–166], reducing spore numbers [167, 168], AM fungal species richness [156, 169] and glomalin production [170].

Conventional or conservation tillage are soil management methods employed [171]. Conservation tillage results in less disturbance when compared with conventional tillage and tends to benefit the soil by conserving aggregate stability and organic matter content [172]. Other reported benefits include higher microbial biomass in conservation tillage due to less disruption and preservation of the hyphal network, contributing to aggregate stability [173, 174]. Reduced tillage increased the abundance of AM fungal and saprotrophic fungal lipids in shallow soil layers [175].

Soil disturbance reduced P uptake from the soil by maize plants, while the uptake of P by canola was not affected [176]. Canola, a non-mycorrhizal host plant, supports the hypothesis that soil disturbance reduces the effectiveness of the mycorrhizal association. McGonigle et al. [177] found that tillage reduced colonization of maize, and the P and Zn contents of maize shoots. The alteration of AM fungal communities by tillage has been reported under field conditions [178]. They demonstrated that colonization by AM fungi from the genus *Scutellospora* was depressed by intensive tillage, while members of the genus *Glomus* were not affected. Fairchild and Miller [179] demonstrated improved AM colonization of maize growing in the undisturbed soil compared to the disturbed soil when amended with P.

Globally, the prevalence of low fertility soils requires amendment with large amounts of inorganic fertilizers and application of pesticides to achieve maximum plant growth and crop yield [180, 181]. The excessive and inappropriate application of chemical fertilizers can cause a series of environmental problems and soil degradation. Balzergue et al. [182] found that the high P concentrations in plants induced by high P fertilization inhibited mycorrhizal symbiosis. Symbiosis modulating

#### *Mitigating Climate Change: The Influence of Arbuscular Mycorrhizal Fungi on Maize… DOI: http://dx.doi.org/10.5772/intechopen.107128*

compounds in root exudates such as strigolactone are also reduced under high P conditions [183]. Under these conditions plants are less reliant on mycorrhizal mediated P uptake and reduce carbohydrate sharing [184–186], this results in a decreased supply of soluble carbohydrate in roots reducing appressorial formation and new colonization [183, 184]. These phenomenal impact AM colonization, arbuscule formation and active P transfer to plants [187]. Some AM fungi can be relatively susceptible to fungicides, particularly when applied to the seed or the soil [188] while other fungicides can also stimulate mycorrhizal growth [189]. Fungicides such as flutolanil, azoxystrobin, fenpropimorph and fenhexamid can inhibit spore germination of *Rhizophargus irregularis* [190, 191]. The insecticide, oxamyl reduced root colonization by a commercial *Funneliformis mosseae* inoculum [192], and azadirachtin inhibiting *Claroideoglomus etunicatum* in the field causing a significant shift in the AM fungal community [193].

The response of AM fungi to agrochemicals is both substance- and dose-dependent. A field experiment showed that most AM fungi belonging to the *Glomus* group were sensitive to high levels of herbicide nicosulfuron which accumulated in soil due to repeated applications in later culture cycles [194]. Atrazine has been used as an agricultural herbicide worldwide, mostly on maize, sorghum, and sugarcane. Studies on maize showed a significant reduction in AM fungal spores [181] and AM colonization [195]. Makarian et al. [196] found a significant effect of the herbicide (metribuzin) on maize dry weight where an increase in herbicide concentration resulted in a decrease in the maize dry weight. Low herbicide concentrations resulted in increased shoot height of AM plants than when applied at high concentrations suggesting that mycorrhizal fungi can alleviate crop stress under lower doses of the herbicide [196].

The extensive use of agrochemicals reduces ecosystem functioning, contributing to soil and water degradation [197]. It also exerts deleterious effects on human health, mainly through the exposure of workers [198–200] and the intake of contaminated food crops [201]. Therefore, increasingly, the enhancement of more biologically based cultivation for safer and healthier food is a rising need, along with finding alternatives to replace agrochemicals in plant production [202–204]. The use of biofertilizers appears to be a natural option, particularly in low agrochemical input systems, because of their capacity to maintain long term soil fertility and sustainability by improving the uptake efficiency and availability of nutrients to plants [205]. Plants inoculated with AM fungi not only have improved growth but also have superior food quality properties, such as increased antioxidants, vitamins, and minerals [206]. AM fungal benefits related to maize are summarized in **Table 1**.

Monoculture is the cultivation of a single crop over a large area over consecutive years [241] and was adopted as a means to increase production [242]. Cultivated crops usually have identical genetic similarities, uniform growth patterns, and resistance to certain common diseases in monoculture. This system includes crop varieties uniquely suited to the specific conditions of a particular location [243]. This approach is criticized for its environmental impacts and is known as one of the major causes of soil degradation due to nonrotational cropping [244].

Hijri et al. [243] found that in continuous maize monoculture diversity of AM fungi decreased but found high diversity in long term field experiments where low-input agriculture involving crop rotation provided better conditions for their preservation. Sangabriel-conde et al. [245] investigated the AM fungal symbioses in native maize landraces at different levels of phosphorus fertilization. They showed a high diversity of AM fungi, most of which colonized several maize varieties, was best achieved at a moderate P level.


#### **Table 1.**

*Compendium of studies showing effect of arbuscular mycorrhizal (AM) fungi on maize.*

One of the most important soil properties is its structure [246]. Soil structure results from the iterations of the soil's chemical, physical and biological factors [247, 248]. Soil management practices, especially tillage systems, affect almost all soil properties, including AM fungi activity, diversity, and glomalin production [248].

Arbuscular mycorrhizal fungi have essential functions in the construction of the soil structure by acting on the formation and stabilization of the aggregates [247, 249–251]. The effect of AM fungi on soil aggregation is a result of ERM growth into the soil matrix creating the skeletal structure that physically entangles soil particles which along with roots enable microaggregates to form in the soil. Microaggregates form larger aggregated [251] via the production of a soil glycoprotein, glomalin [247, 252–254].

AM fungi account for 5–50% of the biomass of soil microbes [255]. Approximately 10–100 m mycorrhizal mycelium per cm root has been estimated [164], the biomass of the ERM may amount to 54–900 kg/ha [256]. Rilling et al. [120] estimated that pools of organic carbon such as glomalin produced by AM fungi might even exceed soil microbial biomass by a factor of 10–20. Glomalin is present in the soil in large amounts. The concentration of glomalin in soil depends on the vegetation cover and the manner of soil management [257] and ranges from 1.6 to 2.3 mg/g soil [258]. Some examples of glomalin concentration in diverse ecosystems include; Agricultural land 0.3–0.7 mg/g [114, 259]; Boreal forest 1.1 mg/g [260]; Desert 0.003–0.13 mg/g [170, 261]; Temperate forest 0.60–5.8 mg/g [170, 262, 263]; Temperate grassland 0.23–2.5 mg/g [263–265]; Tropical rainforest 2.6–13.5 mg/g [170, 266] and Antarctic region 0.007–0.15 mg/g [267]. For example, in the top 10 cm of a tropical rain forest in Costa Rica up to 12.5 mg of glomalin cm−3was reported [266] and up to 60 mg of glomalin cm−3 in a chrono sequence of Hawaiian soils [120]. Glomalin has a longer residence time in soil than hyphae, allowing for a long persistent contribution to soil aggregate stabilization. For hyphae, the residence time varies from days to months [86, 266], while for glomalin, it varies from 6 to 42 years [120]. The effects of AM

#### *Mitigating Climate Change: The Influence of Arbuscular Mycorrhizal Fungi on Maize… DOI: http://dx.doi.org/10.5772/intechopen.107128*

fungi on soil aggregation are probably more easily detected in nutrient-poor soils with neutral or alkaline soil pH [268]. The management of mycorrhizal fungi and diversity in the soil can be considered a biological approach to improving soil structure [269, 270]. Improved soil structure results in improved water infiltration and can mitigate raindrop impact through higher soil stability, increasing resistance to slaking and reduced particles detachment [271]. Significant decreases in AM fungi hyphae and GRSP concentrations have been correlated to losses of C and N protected in macroaggregates as a result of reduced aggregate stabilization [272].

Maize is an obligatory mycorrhizal species (**Table 1**) readily colonized by many non-host-specific AM fungi [273]. Agricultural techniques employing direct sowing and reduced tillage interfere as little as possible with the soil structure and do not cause tearing of the trunks of mycorrhizal fungi [273, 274] resulting in an increase and activity of soil microorganisms and enzymes, especially in the top 20 cm layer. Roldán et al. [275] examined the effect of different management practices on the soil profile distribution of organic matter and physical and microbiological soil quality indicators in a maize field under subtropical conditions. They concluded that the tillage system significantly affected aggregate stability and glomalin. The increases in glomalin suggested that the proliferation of AM fungi could have mediated the improvement in soil aggregate stability under no-tillage. Investigating the influence of tillage and no-tillage on the mycorrhizal status of a field cultivated with maize or bean [276] revealed that GRSP was greater under no-tillage Maize plants (with a root mass of 450 g m−3) had a more marked effect on improving soil aggregate stability than bean plants (with a smaller root mass of 42 g m−3).
