Preface

Both developing and underdeveloped countries have adopted strategies to produce economically optimal agricultural products to feed the world's growing population, which is expected to reach 9 billion in the first half of this century according to the United Nations Food and Agriculture Organization (FAO). Since the main goal of these strategies was to increase the amount of production, soil productivity was prioritized, whereas the fertility factor of soil was ignored. To increase productivity, chemical fertilizers were used excessively and uncontrollably, which caused many short- and long-term problems in the fertility of the soil, continuity of biodiversity, and the sustainability of the balance in nature. Improper fertilizer applications led to an increase in soil salinity, insufficiency of nutrient elements in soil, increased diseases and pests, pollution of the environment, agricultural lands, and drinking water and rivers, and contributed to climate change, which increased the biotic and abiotic stresses on plants and harmed sustainability. As a result, the use of chemical fertilizers decreased agricultural production in the long term. This outcome triggered the efforts to develop agricultural activities involving organic inputs to regain biodiversity, maintain the ecological balance, and decrease the adverse effects of chemicals on human health.

By definition, a fertilizer is any material of natural or synthetic origin that is applied to soil or plant tissues to provide at least one, but often more, of the nutrients required for plant growth. Most fertilizers that are currently used in commercial agriculture provide the three main nutrients: nitrogen, phosphorus, and potassium. These fertilizers are produced industrially from petroleum and petroleum-based products. On the contrary, organic fertilizers are derived from natural sources such as vegetable matter (e.g., compost and crop residues), animal manure, natural rocks, algae extracts, and so on. They are mostly richer in composition compared to chemical fertilizers and provide more nutritional elements as well as beneficial microorganisms. One of the main advantages of using organic fertilizers is that they increase the resistance of plants against biotic and abiotic stress conditions by boosting their immune systems. Moreover, they provide a slow, long, and sustained release of nutritional elements for plant uptake.

Several natural resources, biological products (beneficial bacteria, lichens, algae, and fungi), mineralization products of plant and animal residues (leonardite, humic acid, rock phosphate, bat manure), fermentation products of waste by worms (worm manure), and products obtained from waste of slaughterhouses (amino acid products) are used in agricultural production as organic fertilizers. Although the use of these environmentally friendly products enables the regeneration of natural resources, improves the productivity and fertility parameters of soil, and contributes to carbon footprint management and sustainability, the substitution of chemical fertilizers with these organic products by producers is still slow due to lack of awareness. These products will get greater recognition only when their benefits are explained thoroughly and scientifically.

Besides the aforementioned natural sources, solid wastes of organic origin in the agricultural and industrial wastes can be converted into new organic products to be used in agriculture or into renewable energy by biogas production technologies. Despite all the benefits, the industrial revolution has also brought an important environmental problem: significant amounts of waste that need to be discarded. The utilization of billion cubic meters/year of agricultural and industrial waste as energy or as organic fertilizer is an important value-added solution to this environmental problem and a profound contribution to sustainability.

Today, sustainable use of agricultural soils is no longer a preference, but rather is a mandatory requirement due to the abiotic adverse conditions such as drought and soil degradation caused by global climate change. For this reason, incorporation of organic fertilizers into the soil is essential to develop the cluster structure (aggregate) that holds the soil particles together, increases the amount of organic matter in the soil, regulates the soil pH, and decreases salinity to increase the water-retention capacity as well as the water and air order of the soil. The use of organic fertilizers ensures both the productivity/fertility of the soil and the sustainable production of healthy food products to feed the increasing world population. Therefore, there is a dire need to increase the awareness of each and every stakeholder in the agricultural industry about the benefits of organic inputs and to rapidly include these inputs in the existing agricultural models, which will provide maximum efficiency with minimum or no negative impact on the environment and increase yield per unit of land. The selection of proper fertilizers and their rational use are the key factors to overcoming the challenge of establishing sustainable economic production. Not only is the type of organic fertilizers used important for a successful outcome, but so are the application method, time, and dosage. It is important that national administrators and suppliers promote the use of organic inputs, educate producers, and ensure the availability of organic products in the market.

This book provides an update on the sources, production, and applications of organic fertilizers and highlights their importance in terms of sustainable agriculture, biodiversity, and the environment. It presents new approaches, ideas, and trends to scientists and producers in this field on how to (1) increase the resistance of plants against biotic and abiotic stress conditions and (2) increase the effectiveness of chemical fertilizers while decreasing the amounts used by using organic inputs that are composed of hormones, antioxidants, enzymes, and amino acids.

> **Metin Turan** Yeditepe University, Istanbul, Turkey

**Ertan Yildirim** Atatürk University, Erzurum, Turkey

## **Chapter 1**
