CHAPTER 1 Advances in Clay Research for Sustainable Agriculture
DEBARUP DAS1*, SONALIKA SAHOO2, RUMA DAS1, and SAMAR CHANDRA DATTA1
1 Division of Soil Science and Agricultural Chemistry, ICAR Indian Agricultural Research Institute, New Delhi, Delhi 110012, India
2 Division of Soil Resource Studies, ICAR National Bureau of Soil Survey and Land Use Planning, Nagpur, Maharashtra 440033, India
ABSTRACT
Sustainability of agriculture is crucial to meet the food requirement of ever-growing population. Hence, management practices ought to have the ability to augment the use efficiency of agro-inputs, minimize environmental pollution, and maintain or improve soil quality. With the advancements made in clay research, natural and modified clay minerals along with zeolites are gaining considerable importance in agricultural sector. Owing to some unique physical and chemical characteristics (surface reactivity, surface area, etc.), low cost of production, easy availability, and many other reasons, clay minerals have great potential for use in multiple aspects of agriculture. for instance, they can be used for preparation of slow-release formulations of agrochemicals to increase the use efficiencies of the latter and lower negative impact on environment. Natural and modified clay minerals and zeolite have also showed their potential for remediation of soil and water, which are polluted with various inorganic contaminants, for example, heavy metals (e.g., lead, cadmium, chromium, etc.), metalloids (e.g., arsenic), nitrate (NO3-), bicarbonate (HCO3-), etc.; various radio nuclides; and organic contaminants such as dyes, polyaromatic hydrocarbons, etc. Clay minerals and their modified products can be employed to improve soil quality by increasing carbon sequestration potential, water and nutrient holding capacity, structure, and buffering capacity of soil. Furthermore, clay minerals can also be employed to increase shelf-life and facilitate handling of agricultural produce through improving quality of packaging materials. This chapter describes the various applications of clay minerals from the viewpoint of agricultural sustainability.
1.1 INTRODUCTION
Sustainability can be defined as to âmeet the needs of the present without compromising the ability of future generations to meet their own needsâ (Keeble, 1988). To make agriculture a sustainable affair, we have to minimize the use of nonrenewable inputs; pick up strategies to maintain or improve environmental quality; integrate biological and ecological processes for better crop growth; and rely more upon precise, resource-efficient (i.e., nutrients and energy), and cost-effective techniques that are in congruence with nature and accessible by farmers (Tomich et al., 2004; Manjaiah et al., 2019). Out of many ways leading toward agricultural sustainability, suitable application of clay minerals could be one. Owing to numerous advancements made in clay research during the past few decades, it has been possible to use different clay minerals (without or with modifications) and also zeolite (a tectosilicate) in a number of agricultural applications, namely, nutrient delivery, pesticide delivery, remediation of polluted soil and water, as amendments in a number of specific problems, and packaging material for agricultural produce. Natural clay minerals already present in soil have vital role in sequestering carbon (C), as some of them form strong bonds with organic matter, and reduce their mineralization and subsequent emission of CO2 into the atmosphere (Das et al., 2019a). Soilâs native clay minerals can also indicate deterioration in soil health under long-term mismanagement (Das et al., 2019b).
Controlled-release fertilizers developed by means of clay minerals can enhance nutrient use efficiency through better synchronization between nutrient release from fertilizer and nutrient uptake by plants (Shaviv, 2000). Similarly, clay-based formulations for pesticides can prevent losses and cause lesser contamination of environment (Manjaiah et al., 2019). Lesser rate of application, sustainable supply of nutrients and plant protection chemicals, and lesser environmental pollution are the advantages of such clay-based controlled-release fertilizers and pesticides (Ni et al., 2010; Bhardwaj et al., 2012). Not only prevention, but also for remediation of polluted soil and water, natural and modified clay minerals and zeolite have been found useful (Manjaiah et al., 2018, 2019; Sarkar et al., 2019; Mukhopadhyay et al., 2019a, 2019b, 2020). Apart from remediation of polluted soil and water, clay minerals can also be used as amendments to alleviate a number of soil-related problems too. for instance, some clay minerals have been found useful to enhance water and nutrient holding capacity, reduce nutrient leaching and runoff, improve soil structure, buffering capacity, etc. (Karbout et al., 2015; Ajayi and Horn, 2016; Padidar et al., 2016; Tahir and Marschner, 2017; Saurabh et al., 2019). Clay minerals along with polymers can also be used to make cost-effective packaging materials for transport and marketing of agricultural produce.
Some of the recent advancements made in clay research and their findings showing the potential and role of natural and modified clay minerals along with zeolite in attaining agricultural sustainability are discussed in the following sections.
1.2 ADVANCES IN CLAY RESEARCH FOR SUSTAINABLE MANAGEMENT OF AGROCHEMICALS
Agrochemicals (fertilizers and pesticides) have been extensively used in agriculture worldwide for decades and have contributed toward substantial increase in food production. Unfortunately, only a small part of applied agrochemicals reaches the anticipated target because of their volatilization, leaching, and quick degradation, leading to serious ecological problems (Ravier et al., 2005). Pesticide contamination of surface and groundwater is a major problem as they are potentially hazardous to human, animal, and biodiversity altogether. Likewise, fertilizer leaching and volatilization cause eutrophication of water bodies, greenhouse gas emission, and various healthrelated problems. The focus on slow-release formulation (SRF) or controlled-release formulation (CRF) of agrochemicals has largely increased in the past few years because of the urge to realize sustainability in on-going systems, that is, to enhance economic efficiency and better health and nutrition along with minimum socio-environmental problems caused by excessive use of agrochemicals. With SRF/CRF, the agrochemical is released gradually over a longer time period, thus limiting the amount immediately available for transport processes, which, in turn, minimize volatilization and leaching losses and reduce negative impact on environment (Fu et al., 2018).
Clay minerals perform important functions in multitude of agricultural applications due to their chemical surface functionality and surface structure. Natural and modified/functionalized clays have been gaining interest owing to their potential as well as successful applications in controlled/slow-release systems and/or as modifiers (Gerstl et al., 1998; Armstrong et al., 2000; FernĂĄndez-PĂ©rez et al., 2004; Hocine et al., 2004; HermosĂn et al., 2006; Sanchez-Martin et al., 2006). Clay-based CRFs mostly involve montmorillonites (Gerstl et al., 1998; Chevillard et al., 2012a), kaolinites (Singh et al., 2009), and bentonites (FernĂĄndez-PĂ©rez et al., 2004; CĂ©spedes et al., 2013; Sahoo et al., 2014, 2016).
1.2.1 SUSTAINABLE MANAGEMENT OF FERTILIZERS
1.2.1.1 CLAY MINERALS AS FILLER OR CARRIER OF NUTRIENTS
Initially, clay minerals have been used as filler materials in many fertilizers. Clays such as sodium bentonite, montmorillonite, kaolin, attapulgite, sepiolite, and tectosilicate such as zeolite are used as modifying agents to improve fertilizer handling quality. By virtue of their crystalline geometry, clay (bentonite, kaolin, attapulgite, or sepiolite) or zeolite addition to urea melt or urea synthesis liquor can impart good anticaking and nonfriability characteristics to the urea granules. Palygorskite and sepiolite, when blended with bentonite, act as excellent absorbents and used as carriers for agrochemicals in agricultural applications. Clays such as sepiolite, attapulgite, and bentonite can be used in suspension application of fertilizers due to their thickening ability. Suspension formulations are fluid mixtures of solid mater...
