Managing Soils for Reducing Dependence on Chemicals and Import of Resources into Agroecosystems

Rattan Lai

CONTENTS

• 14.1 Introduction.........................................................................................................................339
• 14.1.1 The Soil-Climate-Vegetation Nexus.....................................................................339
• 14.1.2 Soil Quality and Functionality...............................................................................341
• 14.1.3 Sustainability of Agroecosystems..........................................................................341
• 14.2 Strategies to Reduce Use of Chemical Fertilizers and Minimize the Environmental

Impact..................................................................................................................................343

• 14.3 Strategies to Reduce Dependence on Chemical Fertilizers................................................344
• 14.3.1 Factors Affecting the Choice of Site-Specific Fertilizer Options..........................345
• 14.4 Addressing the Fertilizer Addiction....................................................................................346
• 14.4.1 Global Food Demand by 2050...............................................................................346
• 14.4.2 Managing Soil Organic Matter and Soil Quality..................................................346
• 14.5 General Conclusions...........................................................................................................347
• 14.5.1 Meeting Global Food Demand by 2050.................................................................347
• 14.5.2 Way Forward..........................................................................................................347

References......................................................................................................................................348

INTRODUCTION

14.1.1 The Soil-Cumate-Vegetation Nexus

The dynamic interaction between soil biota and the climate (Jenny 1941) is the basis of soil functions for humans and for nature (Figure 14.1). Drastic perturbations of the soil-biota-climate nexus, by natural phenomena or anthropogenic activities, can adversely impact the provisioning of essential ecosystem services and also lead to some disservices (e.g., accelerated erosion, disruption in elemental and water cycling, energy imbalance, and shifts in flora and fauna). Perturbation of the nexus in agroecosystems is also the cause of the high import of resources such as fertilizers, pesticides, tillage, irrigation, etc. Such ameliorative measures aggravate the environmental impact and footprint of agroecosystems. Among the symptoms of drastic perturbations are the drought-flood syndrome, eutrophication and contamination of waters (e.g., algal bloom, hypoxia/anoxia of coastal waters), desertification, heat waves, and extreme events. Anthropogenic activities are also impacting the carbon (C) cycle and the attendant global warming (Lai 2004, 2010; Jackson et al. 2017; Chapin III et al. 2009), the water cycle and the associated pedological and hydrological drought (Lai 2013), and hypoxia (Zillen et al. 2008). Therefore, a judicious and prudential management of the nexus (Figure 14.1) can minimize the need for the import of resources and enhance sustainability.

FIGURE 14.1 The soil-biota-climate nexus is the basis for provisioning of essential ecosystem services for nature including humans.

Global fertilizer use has increased drastically since the 1960s and is still increasing. Total annual average fertilizer use between 2015 and 2020 is about 200 million Mg and increasing (Table 14.1). The use of chemical fertilizer since 1960 is considered responsible for feeding a large proportion of the world population. The number of people (billions) fed by fertilizer is estimated at 0.4 in 1960, 0.9 in 1970, 1.34 in 1980. 2.13 in 1990, 2.70 in 2000, and 3.54 in 2015 (Table 14.2; Richie 2017). However, the environmental impact is very high. The global average ratio of N:P₂0₅:K₂0 is 3.3:1.3:1.0, and has a decreasing trend over time. However, the ratio is more skewed in favor of N in some emerging economies (i.e., India) because of high subsidies for N. The ratio should be

TABLE 14.1

Global Fertilizer Nutrient Demand

Source: FAO, World Fertilizer Trends and Outlook to 2020: Summary Report, FAO, Rome, Italy, 14 pp, 2017.

TABLE 14.2

World Population Supported with and without Fertilizer

Source: Richie, H., How Many People Does Synthetic Fertilizer Feed?, https://ourworldindata.org/how- many-people-does-synthetic-fertilizer-feed, 2017.

about 4:2:1 for input of N:P₂0₅:K₂0. Whereas prudential and supplemental use of chemical fertilizers, supplemental irrigation, and tillage are justified as ameliorative strategies, indiscriminate and excessive/unbalanced use of inputs (i.e., pesticides, fertilizers, flood-based irrigation) can lead to disruption of the nexus and the attendant degradation of the environment. In this regard, management of the soil surface is critical to sustainable use of agroecosystems (Wassenaar et al. 2006; Amundson et al. 2015; Zhao et al. 2019). Management of soil C concentration and stock is essential to several of these services and benefits (Lai 2004, 2010, 2018b; Milne et al. 2015).

14.1.2 Soil Quality and Functionality

Soil quality is indicative of its capacity to sustain the nexus (Figure 14.1) and generate ecosystem services in perpetuity. There are some key soil properties (Zhao et al. 2019) with a strong control on soil quality and functionality (Figure 14.2). For example, concentration of soil organic carbon (SOC) affects soil bulk density (Ruehlman and Korshens 2009), soil erodibility (Wang et al. 2013; Wischmeier and Manneing 1989), plant-available water capacity (Hudson 1994), microbial processes (Wieder et al. 2013), and storage of atmospheric carbon dioxide (Lai 2018a; Lai et al. 2018; Wiesmeieret al. 2019). Identification and management of these key soil properties is critical not only to achieving sustainable agriculture but also to advancing sustainable development goals (SDGs) or the Agenda 2030 of the United Nations (Lai 2018b). Excessive, indiscriminate, and unbalanced use of reactive nitrogen (N, chemical fertilizer) has created environmental issues (Sebilo et al. 2013) and jeopardized the safe operating space (Rockstrom et al. 2009). The perturbation of the N cycle by the use of chemical fertilizers and leguminous crops including green manure (Galloway et al. 2003, 2004) has also perturbed the global C cycle because of their coupled cycling (Lai 2010) and possibility of increased mineralization of soil organic matter or SOM (Khan et al. 2007; Mulvaney et al. 2009).

14.1.3 Sustainability of Agroecosystems

Sustainability is a multidimensional attribute (Figure 14.3) (Lai et al. 2016b). It is composed of environmental, social, economic, and institutional components. Management of the soil-biota-climate

FIGURE 14.2 Ten key soil properties that impact soil quality and functionality.

FIGURE 14.3 Components of the multidimensional sustainability.

nexus (Figure 14.1) is also critical to advancing multidimensional sustainability. All components interact with one another (Figure 14.3), and are integral to advancing multidimensional sustainability. Indeed, environmental/ecological sustainability, the key component of the whole (Figure 14.3), depends on other components (i.e., social/cultural, economic, and institutional). The economic aspect, often assessed on a short-term basis, needs an objective consideration. The long-term sustainability of agroecosystems depends on the economic profitability for nature rather than just for humans, and is a long-term issue over centennial and millennial scales rather than on an annual scale.

Therefore, the objective of this chapter is to synthesize the material presented in the previous 13 chapters and outline some research and development priorities so that dependence on chemical fertilizers and the environmental footprint of agroecosystems are minimized.