The Synergistic Effects of Humic Substances and Biofertilizers on Plant Development and Microbial Activity: A Review

Abstract

Agroecosystem and ecological cycling loops are open when considering the reutilization of inputs applied in farming areas. Non-renewable resources have been transformed or relocated from the air, water and land into the system and are flowing out as wastes rather than reusable, recyclable resources. This current environmental situation is promoting the development of methods able to optimize nutrient cycling, minimize use of external inputs, and maximize input use efficiency. Some humic products are derived from lignin found in wheat straw and biofertilizers as compost and manure teas can be made using residues. Also, these biostimulants might decrease the necessity of synthetic inputs. This review strives to enhance our understanding of the conjunctive use of humic substances (HS) and biofertilizers. The biostimulant effects of each of these compounds are shown in the literature. Thus, our review question is whether the combined application of HS and biofertilizers can promote synergy between both compounds and potentially more efficacy. The effects promoted by using HS plus biofertilizers on plants and microorganisms are very interconnected, so sometimes these effects can be confounded. For instance, the root elongation promoted by HS might increase hyphal fungi colonization. Therefore, this review as divided in three sections: Responses of plants, fungi and bacteria. The findings indicate that the source and application rate of HS will have a strong impact on whether plant growth and microbial activity significantly improved. The microbial species and plant type also influence the response to HS. The prospects of the conjunctive use of and biofertilizers to stimulate plant development and microbial activity in agricultural systems are theoretically substantial when considering the total number of studies included in this review.

Effect of organic biostimulants on cannabis productivity and soil microbial activity under outdoor conditions

“…Similarly, the use of biofertilizer increased plant height on pomegranate ( Punica granatum L.) (Aseri et al 2008 ) and sunflower ( Helianthus annus L.) (Akbari et al 2009 ). On cannabis, Conant et al ( 2017 ) and Da Cunha Leme Filho et al ( 2020a , b ) reported greater cannabis height due to biostimulant applications under indoor conditions.

Fig.

…”

“…As soil CO 2 evolution is directly related to soil microbial activity (Frankenberger Jr and Dick 1983 ), the application of HA positively affects microbial growth due enzymatic function (Visser 1985 ) and carbon source (Flaig 1964 ). A review evaluating the effects of HA on microbial activity indicated that HA dose and bacteria and fungi species have an important influence on whether or not the activity measurement will be increased (Da Cunha Leme Filho et al 2020a , b ).…”

“…There are far less studies testing the use of biostimulants on cannabis when compared to other plants. Humic acid application on cannabis presented positive results in terms of canopy uniformity (Bernstein et al 2019 ) and higher plant height, chlorophyll content, and photosynthetic efficiency (Da Cunha Leme Filho et al 2020a , b ). According to Turner et al ( 1978 ), cannabinoid compounds are present in all aerial parts of the cannabis plant, and thus, the research to validate the responses of cannabis to the application of biostimulants can be very important because biomass increase can potentially lead to higher cannabinoids production, which is the most valuable sub-product.…”

Carbon Dots as Solubilizing Agent for Insoluble Phosphates in Enhancing Soil Fertility

“…have suggested that organic matter, especially humic (HA) and fulvic (FA) acids, may dissolve insoluble phosphates, increasing phosphorus mobility by forming humic acid‐metal‐phosphate complexes. The effect of humic acids, fulvic acids on the solubilization of phosphate and, in general, their cooperation in better nutrient uptake by plants have been well discussed in the literature [26–28] . In general production of organic acid leads to a decrease in pH.…”

“…The effect of humic acids, fulvic acids on the solubilization of phosphate and, in general, their cooperation in better nutrient uptake by plants have been well discussed in the literature. [26][27][28] In general production of organic acid leads to a decrease in pH. However, Asea et al [29] found that no correlation exists between the pH and the amount of P solubilized.…”