Preface

Present in soil, water, and geological organic deposits, humic substances are the most widespread organic compounds, naturally occurring from the physical, chemical, and microbiological transformation of biomolecules. Humic substances represent about 25% of the total organic carbon on the Earth and comprise up to 75% of the dissolved organic carbon in water, making them important for multiple environmental processes in both soil and aquatic systems.

Based on their solubility, humic substances can be fractionated into humic acid, fulvic acid, humin, and some microelements. Humic acid includes long-chain aggregates soluble in alkali, while fulvic acid is a mixture of short-chain compounds soluble in both acidic and alkaline solutions. Humin, in contrast, constitutes the non-soluble fraction of the humate. This classification is based only on superficial criteria and does not indicate chemical behavior or provide insights into chemical structures.

Humification, or the set of processes leading to humic substances, is a set of reactions occurring either in sequences or simultaneously and affecting at varying speeds an extreme diversity of substrates. These reactions are essentially biochemical in nature, but purely chemical processes can also be involved. Physical factors, such as temperature or the humidity of the surrounding environment, also determine the formation of humic substances at various stages. Humification, therefore, appears to be a complex process in which biological activity plays a major role in the short term, but the slow evolution of humic compounds due to external conditions may gradually modify the properties of the humus.

Despite many decades of extensive studies, the formation mechanisms of humic substances, as well as their structure, are still a subject of discussion and controversy. The content of this book revolves around the structure and dynamics of humic substances, their physicochemical and biological properties, and the technics of their extraction and characterization. The book also sheds light on recent advances and applications of humic substances in agriculture, environment, industry, and medicine.

**II**

**Chapter 8 139**

**Chapter 9 153**

Chemical Characteristics of Humic Substances in Nature *by Claudio Fernando Mahler, Nicoly Dal Santo Svierzoski* 

Sewage Sludge to Fertilise Durum Wheat: Effects on Crop and Soil

*and Cassiano Augusto Rolim Bernardino*

*by Pilar Mañas and Jorge de las Heras*

**Abdelhadi Makan** Abdelmalek Essaadi University, Tétouan, Morocco

**1**

**Chapter 1**

**Abstract**

**1. Introduction**

non-soluble fraction of the humate.

Humic Substances: Prospects for

Use in Agriculture and Medicine

Humic substances are the naturally occurring biogenic, heterogeneous organic compounds resulting from the decomposition of plant, animal and microbial residues, over many thousands of years. Research into humic substances have found them to be beneficial not only for crop production, but for human and animal health also. Humic substances influence crop yields by affecting soil texture, water retention, nutrient buffering capacity and microbial diversity. Their stimulatory effects on plant growth and physiology can be ascribed to enhanced nutrient uptake, hormonal activity with root growth and proliferation, activation of antioxidant defense under various abiotic stresses. Furthermore, their potential to remove toxic pollutants from soil as well as aquatic systems might resolve the problem of degrading environment. Positive effects of humic substance on soil as well as crop without harming the environment make humic acid a sustainable solution for crop production. The antioxidant, immunomodulatory, anti-inflammatory, detoxifying and nutritional properties of humic substances opens up new avenues for their medical applications. Still, more research is needed to completely explore their potential. This chapter will summarize and review information about the prospects of using humic substances in agriculture and medicine.

**Keywords:** Humic substances, Fulvic acid, Humic acid, agriculture, medicine

Humic substances (HS) are soil-derived substances that form one of the vast reservoirs of organic carbon in nature. HS are primarily produced by physical, chemical and microbial degradation and transformation of plant and animal tissues (humification process) over millions of years. They constitute the bulk of organic matter of the soil – humus, peat, lignites and also brown coal. HSs may also be produced as a by-product of the synthetic oxidation reactions of phenolic compounds. Humic substances contain carbon, hydrogen, oxygen and nitrogen with small amounts of sulfur and phosphorus. They are a mixture of acids that can be fractionated on the basis of differences in their solubility into humic acid (HA), fulvic acid (FvA) and humin fractions, beside ulmic acid, and some microelements. Humic acid includes aggregates of long chain, high molecular weight compounds, soluble in alkali, while FVA is a mixture of short chain, low molecular weight compounds, soluble in both acidic and alkaline solutions. Humin, in contrast, constitutes the

Owing to their unique structural and chemical properties, humic substances make an excellent soil amendment. They offer beneficial impacts in terms of overall soil structure, water holding capacity and nutrient availability in the soil along with

*Priya Goel and Madhu Dhingra*

## **Chapter 1**
