**5. Yield increase X Arbuscular mycorrhizal fungi**

Arbuscular mycorrhizal fungi (AMF) are the main microorganisms that compose the majority of the microbial biomass in cultivated soils. About 80% of plants are symbiotic with these fungi, and they are an important factor in improving soil quality and crop growth.

There is a great nutritional benefit for plants influenced by arbuscular mycorrhizal fungi. Phosphorus stands out among the nutrients that combine with the Arbuscular Mycorrhizal Fungi to facilitate uptake. This nutrient is very low in soil solutions due to sorption and precipitation reactions, also immobilization, this kind of behavior is common in heavily weathered soils. AMF hyphae help in accessing this nutrient because they utilize more soil and places that are difficult for plants' roots to access.

There are also reports in the literature that these fungi assist in the uptake of sulfur, potassium, nitrogen, zinc, copper, magnesium, iron, manganese, and calcium. Therefore, plants with high levels of mycorrhizal colonization are expected to be more tolerant to eventual nutrient unavailability and less dependent on the application of external inputs than plants with low symbiosis.

Indirectly, mycorrhizae also improve plant tolerance to nematode and disease attacks on coffee, increasing plant vigor. In addition, improving tolerance to pest and disease attacks is important because these organisms cause significant yield losses [17].

As seen earlier, AMF is an important stress reliever. These microorganisms increase drought resistance because they provide plants with increased water uptake. The increased hydration and stomatal conductance in plants associated with mycorrhizae promote transpiration, the main mechanism for cooling the leaves. Thus, hypothetically, coffee plants with a high degree of symbiosis are better able to withstand a high-temperature summer and suffer less scalding. These fungi also increased tolerance to metal toxicity such as copper, zinc, and aluminum and reduced damage caused by high osmotic pressure.

Topical application of amide and ammonia nitrogen fertilizers is also a major problem in these systems, as excessive acidification of the wetting bulb can increase the solubility of metal micronutrients to toxic levels [18]. Thus, mycorrhizae can be an important stress reliever in irrigated coffee farming improving soil quality the extensive development of extra-radicular hyphae and secretion of glomalin by these fungi are important mechanisms for improving soil physical, chemical, and biological properties [19].

*Introductory Chapter: Mycorrhizal Fungi – A Current Overview on Agricultural Productivity… DOI: http://dx.doi.org/10.5772/intechopen.109021*

Arbuscular mycorrhizal fungi improve soil structure by connecting particles and forming stabilized aggregates. This is due to the mechanical effects of extra-radicular hyphae growth and the secretion of glomalin. This glycoprotein exhaled by fungi has adhesive properties in the soil, and its content has been correlated with aggregate stability and organic matter. It increases the carbon content in the soil, stimulating biological activity because there is more food for the microorganisms.
