Soil health and global sustainability: translating science into practice

Abstract

Interest in the quality and health of soil has been stimulated by recent awareness that soil is vital to both production of food and fiber and global ecosystems function. Soil health, or quality, can be broadly defined as the capacity of a living soil to function, within natural or managed ecosystem boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality, and promote plant and animal health. Soil quality and health change over time due to natural events or human impacts. They are enhanced by management and land-use decisions that weigh the multiple functions of soil and are impaired by decisions which focus only on single functions, such as crop productivity. Criteria for indicators of soil quality and health relate mainly to their utility in defining ecosystem processes and in integrating physical, chemical, and biological properties; their sensitivity to management and climatic variations; and their accessibility and utility to agricultural specialists, producers, conservationists, and policy makers. Although soils have an inherent quality as related to their physical, chemical, and biological properties within the constraints set by climate and ecosystems, the ultimate determinant of soil quality and health is the land manager. As such, the assessment of soil quality or health, and direction of change with time, is the primary indicator of sustainable management. Scientists can make a significant contribution to sustainable land management by translating scientific knowledge and information on soil function into practical tools and approaches by which land managers can assess the sustainability of their management practices. The first steps, however, in our communal journey towards sustainable land management must be the identification of our final destination (sustainability goals), the strategies or course by which we will get there, and the indicators (benchmarks) that we are proceeding in the right direction. We too often rush to raise the sails of our ‘technological’ ship to catch the wind, before knowing from where it comes or in properly defining our destination, charting our course, and setting the rudder of our ship. Examples are given of approaches for assessing soil quality and health to define the sustainability of land management practices and to ‘translate our science into practice’.

Introduction

Interest in evaluating the quality and health of our soil resources has been stimulated by increasing awareness that soil is a critically important component of the earth’s biosphere, functioning not only in the production of food and fiber but also in ecosystems function and the maintenance of local, regional, and global environmental quality (Glanz, 1995). Soil health has been broadly defined as the capacity of a living soil to function, within natural or managed ecosystem boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality, and promote plant and animal health (Doran et al., 1996, Doran et al., 1998). Soil health can change over time due to natural events or human impacts. It is enhanced by management and land-use decisions that weigh the multiple functions of soil and is impaired by decisions that focus only on single functions, such as crop productivity. Thus, balance between soil function for productivity, environmental quality, and plant and animal health is required for optimal soil health. Criteria for indicators of soil quality and health relate mainly to their utility in defining ecosystem processes and integrating physical, chemical, and biological properties; their sensitivity to management and climatic variations; and their accessibility and utility to agricultural specialists, producers, conservationists, and policy makers. Although soils have an inherent quality as related to their physical, chemical, and biological properties within the constraints set by climate and ecosystems, the ultimate determinant of soil quality and health is the land manager. As such, the assessment of soil quality or health, and direction of change with time, is a primary indicator of sustainable management.

The sun is the basis for most life on earth. It provides radiant energy for heating the biosphere and for the photosynthetic conversion of carbon dioxide (CO₂) and water by green plants into food sources and oxygen for consumption by animals and other organisms (Fig. 1). Most living organisms utilize oxygen to metabolize these food sources, capture their energy, and recycle heat, CO₂, and water to the environment to begin this cycle of ‘life’ again. Decomposition processes, as mediated by organisms in soil, play a predominant role in completing this cycle of life, in recycling of building block nutrients to plants and C as CO₂ to the atmosphere. Thus, the thin layer of soil covering the surface of the earth is a major interface between agriculture and the environment and represents the difference between survival and extinction for most land-based life (Doran et al., 1996). The quality and health of soil determine agricultural sustainability (Acton and Gregorich, 1995, Papendick and Parr, 1992) and environmental quality (Pierzynski et al., 1994) which jointly determine plant, animal, and human health (Haberern, 1992).

Dramatic change has recently occurred in our thinking about agricultural development, our use of natural resources, and stability of the global environment. Even economically undeveloped countries are increasingly more aware and concerned about ecosystem health, the quality of the environment, and rates of resource consumption (Mermut and Eswaran, 1997). Increasing human populations, decreasing resources, social instability, and environmental degradation threaten the natural processes that sustain the global ecosphere and life on earth (Costanza et al., 1992, Postel, 1994). With little new agricultural land to develop, meeting the food needs of future populations will require a doubling of crop yields. However, under current food production practices this will greatly increase inputs into agricultural production systems, thereby vastly increasing opportunity for environmental pollution and degradation and depletion of natural and non-renewable resources (Power, 1996). To sustain agriculture and the world for future generations, we must act now to develop production systems which rely less on non-renewable petrochemical based resources; rely more on renewable resources from the sun for our food, fiber, and energy needs; and achieve the ecological intensification needed to meet the increased future food demand (Cassman, 1999).

Global climate change, depletion of the protective ozone layer, serious declines in species biodiversity, and degradation and loss of productive agricultural land are among the most pressing concerns associated with our technological search for a higher standard of living for an ever-growing human population. Past management of agriculture and other ecosystems to meet the needs of increasing populations has taxed the resiliency of soil and natural processes to maintain global balances of energy and matter. The quality of many soils in the Americas and elsewhere has declined significantly since grasslands and forests were converted to arable agriculture and cultivation was initiated. In particular, mechanical cultivation and the continuous production of row crops has resulted in physical soil loss and displacement through erosion, large decreases in soil organic matter content, and a concomitant release of organic C as CO₂ to the atmosphere (Houghton et al., 1983). Within the last decade, inventories of soil productive capacity indicate human-induced degradation on nearly 40% of the earth’s arable land as a result of soil erosion, atmospheric pollution, extensive soil cultivation, over-grazing, land clearing, salinization, and desertification (Oldeman, 1994). Indeed, degradation and loss of productive agricultural land is one of our most pressing ecological concerns, rivaled only by human caused environmental problems like global climate change, depletion of the protective ozone layer, and serious declines in biodiversity (Lal, 1998). Further, the projected doubling of the human population in the next century threatens accelerated degradation of soils and other natural resources (Power, 1996, Ruttan, 1999). Thus, to preserve agriculture for future generations, we must develop production systems that conserve and enhance soil quality and health. Developing the blueprints for sustainable development, however, will require interaction between society, science, and religious leaders to establish the necessary balance between meeting basic human needs, maintaining environmental stewardship, and achieving intergenerational equity (Bhagat, 1990, Sagan, 1992).

The objectives of this paper are two-fold: (1) to illustrate the intimate linkage between soil health and global sustainability and the critical role of the soil as a major interface with the environment, and (2) to propose indicators of soil quality and health which are useful tools to land managers in assessing the short- and long-term sustainability of their management practices.