## 1 Introduction  
Sustainable agriculture is described as a method that improves the quality of the environment and the resources on which the agriculture sector relies, that supplies the basic human needs for food and fibers, and that improves the living standard of farmers and society in general [1, 2]. It implies the reliable maintenance of agricultural practices for assessing and implementing sustainable crop cultivation. Protecting different field crops against weeds, other crop pests, and diseases is the key factor for the sustainable production of crops [3]. Weeds directly contend with crops for space, light, nutrition, and humidity. Therefore, the intrusion of weeds greatly affects the physiological behavior and development of crop plants [4, 5]. Weeds cause significant crop yield losses--more than 50 percent for some crops if the fields are left unchecked [6]. The strategy for weed control performs a critical role and directly affects global food protection and food productivity. Herbicides developed since the end of the Second World War have been used as the key tool for weed control. At present, the application of herbicides in agriculture creates problems for people and crops and results in environmental degradation and the growth of herbicide-resistant weeds [7]. Consequently, health hazards ensue, and sources of drinking water could become polluted, leading to adverse effects on plants, microorganisms, birds, and fish [8]. It is essential to find an alternative method to develop synthetic herbicides, which might be used for integrated weed control programs to grow crops sustainably. Allelopathy is the biological phenomenon in which plants or plant residues release allelochemicals that affect (usually adversely) other nearby plants [9] and is the best alternative for sustainably controlling weeds in crop fields. The first reason for research on allelopathy is to gain better insight into how plants interact with other life forms via allelochemicals/secondary metabolites. Allelopathy helps to reduce the use of synthetic herbicides, subsequently reducing environmental deterioration, and helps to develop successful methods for sustainable agricultural production [10]. In agro-ecosystems, allelopathy has a significant role not only in plant-to-plant, and plant-to-microorganisms interactions, but also in plant-to-insect or plant-to-herbivore contact [11]. Plants produce various types of allelochemicals, such as phenols and tannins [12]; saponins and alkaloids [13]; flavonoids and terpenoids [14]; amino acids, carbohydrates, and glycosides [15]; and coumaric acid [16]. These substances have herbicidal characteristics such as being able to restrict cell division [17] and reduce the rate of photosynthesis of nearby plants [18]. The effects of phytochemicals on seed germination, seedling growth, and plant development are controlled by the interaction, complexity, and concentration of plants' secondary metabolites [19]. Studies have investigated the use of allelopathic plants and allelochemicals in agriculture for sustainable weed control [20; 21; 22]. Presently, phytochemicals are being investigated in the development of herbicides [23]. _Albizia richardiana_ (Voigt.) King & Prain (local (Banglades) name: rajkoroi) is a large, fast-growing deciduous tree belonging to the family Fabaceae, sub-family Mimosaceae [24]. The leaves of _Albizia richardiana_ are bipinnate, compound, sessile, and small. The flower is stalkless, small, and greenish white. The fruit is thin, long, and whitish brown. This tree species usually grows well in hot and humid areas in Asia, Australia, Madagascar, North America, and Africa, but mainly grows in the tropics of the Old World [25; 26]. The tree can be found in different areas of Bangladesh like Sunamgonj, Chittagong, Barisal, Bagerhat, Jhalukati, Madaripur, and Pirujpur. It is also cultivated as an ornamental and roadside avenue tree [27] and is considered an auspicious tree in Bangladesh [28].