Soil Health and Intensification of Agroecosystems

Mahdi M. Al-Kaisi, Birl Lowery, Mahdi M. Al-Kaisi, Birl Lowery

• Publisher: Academic Press
• Year: 2017
• ISBN:
  9780128054017
• Topic: Technik & Maschinenbau
• Subtopic: Agronomie

Soil Health and Intensification of Agroecosystems examines the climate, environmental, and human effects on agroecosystems and how the existing paradigms must be revised in order to establish sustainable production. The increased demand for food and fuel exerts tremendous stress on all aspects of natural resources and the environment to satisfy an ever increasing world population, which includes the use of agriculture products for energy and other uses in addition to human and animal food.

The book presents options for ecological systems that mimic the natural diversity of the ecosystem and can have significant effect as the world faces a rapidly changing and volatile climate. The book explores the introduction of sustainable agroecosystems that promote biodiversity, sustain soil health, and enhance food production as ways to help mitigate some of these adverse effects.

New agroecosystems will help define a resilient system that can potentially absorb some of the extreme shifts in climate. Changing the existing cropping system paradigm to utilize natural system attributes by promoting biodiversity within production agricultural systems, such as the integration of polycultures, will also enhance ecological resiliency and will likely increase carbon sequestration.

• Focuses on the intensification and integration of agroecosystem and soil resiliency by presenting suggested modifications of the current cropping system paradigm
• Examines climate, environment, and human effects on agroecosystems
• Explores in depth the wide range of intercalated soil and plant interactions as they influence soil sustainability and, in particular, soil quality
• Presents options for ecological systems that mimic the natural diversity of the ecosystem and can have significant effect as the world faces a rapidly changing and volatile climate

Chapter 1

Fundamentals and Functions of Soil Environment

Mahdi M. Al-Kaisi¹, Rattan Lal², Kenneth R. Olson³ and Birl Lowery⁴, ¹Iowa State University, Ames, IA, United States, ²The Ohio State University, Columbus, OH, United States, ³University of Illinois, Urbana, IL, United States, ⁴University of Wisconsin-Madison, Madison, WI, United States

Abstract

Soil is a complex and dynamic natural system. The definition of soil varies widely, as it is dictated by its use and how we perceive it as a society for providing services, food, habitat, and enjoyment, where these functions are essential to soil health or quality. One well-established definition of soil is a medium that includes minerals, organic matter, countless organisms, liquid, and gases that together support life on earth through many services. Soil environment and functions are influenced by the parent materials and forming factors that contribute to the physical, chemical, and biological characteristics of soils. This chapter addresses the basic soil physical, chemical, and biological properties and explores the interrelationships between different soil properties and functions as essential building blocks for a healthy functioning soil system. The soil physical environment includes components of soil structure, aggregation, soil water potential and water movement, and soil thermal regime, along with governing forces. The soil biological environment includes all soil organisms (macro- and microorganisms), soil–plant relationships (plant root–soil interactions), plant growth and soil microorganisms, and plant root interface and nutrient cycling. In addition, the soil chemical environment discussion focuses on soil nutrient capacity and supply, nutrient cycling, and nutrient pathways and mechanisms.

Keywords

Water potential; matrix potential; soil aggregate; soil structure; soil temperature; cations exchange capacity; nutrient cycling; mass flow; diffusion flow

1.1 Introduction

The soil system is complex and dynamic. The definition of soil varies widely, as it is dictated by its use and how we perceive soil as a society for providing services, food, habitat, and enjoyment, where these functions are essential to soil health or quality. One well-established definition of soil is a medium that includes minerals, organic matter, countless organisms, liquid, and gases that together support life on earth through many services. Soil is the foundation for early and modern agriculture, and for human civilization. Most people think of farming or gardening when they think of soils (Brevik, 2005). However, the definition of soil depends on the multiple uses of this medium for different purposes such as farming, engineering, and environment. To a farmer, soil is a medium to produce food, which differs from that of a geologist, who considers soil a natural medium and unconsolidated materials above bedrock. An engineer defines soil as a naturally occurring surface layer formed by complex biochemical and physical weathering processes that contains living matter. Soil is considered capable of supporting plant, animal, and human life by agronomists and pedologists (Brevik, 2005). Soil environment and functions are influenced by the parent materials and forming factors that contribute to the physical, chemical, and biological characteristics of soils. The inorganic fractions of mineral soils generally consist of sand, silt, and clay. The proportion of these different fractions determines soil texture, along with its subsequent chemical, physical, and biological properties. Soil formation progresses in steps and stages that are not distinctly separated. These processes are overlapping, and it may not be possible to know when one stage in soil formation stops and another starts (Huggett, 1998). Soil characteristic depends primarily on the parent materials, and secondarily on the vegetation, the topography, and time. These are the five variables known as the factors of soil formation (Jenny, 1941). The typical development of a soil and its profile is called pedogenesis, which includes physical and chemical processes and disintegration of the exposed rock formation as the soil’s parent material (Hillel, 1998). These loosened materials are colonized by living organisms (plant and animal, micro- and macroorganisms). This process leads to accumulation of soil organic matter (SOM) at and below the soil surface resulting in the formation of an A horizon. Important aspects of soil formation and development include two processes of eluviation (washing out) and illuviation (washing in), where clay particles and other substances, including calcium carbonate, emigrate from the overlay surface, eluvial A horizon, and accumulate in the underlying illuvial B horizon (Jenny, 1941). The formation of the soil profile and its physical, chemical, and biological characteristics through these processes differ from location to location and region to region. In arid regions, for example, salt movement from upper to lower horizons may create physical, chemical, and biological conditions that are different from those in humid areas and the tropical, where there is more of a tendency for leaching of minerals and chemicals through the soil profile because the driving force for this reaction being water, is greater in these environments. Therefore, different soil properties, such as color or SOM concentration, occur in the top soil layer and at subsequent depths of the soil profile (Weil and Brady, 2016). These processes influence soil fertility, water availability, and SOM content, which limit the choice of type of crops and management practices that are essential for sustaining soil health and productivity. Therefore, the level of soil health is different for different soil types.

1.2 Soil Properties and Interrelationships

1.2.1 Soil Physical Environment

The soil physical environment is generally characterized by three distinct phases that include the solid phase that forms the soil matrix, the liquid phase comprised of water in the soil system, called the soil solution, and the gaseous phase or the soil atmosphere. The soil matrix (mineral component) consists of soil particles varying in size, shape, and chemical properties (Fig. 1.1). The formation of the soil matrix through the grouping of different particles with amorphous substances, particularly SOM, when attached to the surface of different mineral particles, form soil aggregates that are essential components of soil health or quality. The formation of soil aggregates determines the soil structure and geometric characteristics of pore spaces in which water and air retention and movement occur (Tisdall and Oades, 1982). The water and air proportions vary in space and time, and the increase in one portion leads to a decrease in another (Fig. 1.2). The relative proportions of the three phases in a soil are not fixed, but are rather dynamic, changing continuously depending on variables such as weather, vegetation, and management by humans. Tillage and cropping systems can significantly impact soil aggregate formation and stability. Generally, soil aggregate formation is highly influenced by plant roots and fungal hyphae as major binding agents for macroaggregates (>0.25 mm), while organic compounds are responsible for the formation of microaggregates (<0.25 mm) (Tisdall and Oades, 1982). Soil structure can influence its environment by providing conditions that impact plant growth such as water availability, nutrient dynamics, and soil tilth (Oades, 1984). One of the quantitative measures to evaluate the soil physical environment is bulk density. This soil property is shaped by soil texture and influenced by management practices through changes in soil structure and porosity. Bulk density is often used as a soil health or quality indicator. Bulk density is defined as mass per volume (kg m⁻³ or Mg m⁻³) as described by the following equation:

${\rho }_b=\frac{M_s}{V_t}$ (1.1)

(1.1)

Figure 1.1 Schematic representation of pore spaces between soil aggregates.

Figure 1.2 Schematic representation by volume of different soil components at optimal condition for plant growth. Total solid matter components (mineral and organic matter) make up 50% and the pore space 50% of the total soil volume, which is divided equally between water and air. The water and air volumes are exchangeable as indicated by the arrows, depending on soil moisture conditions.

where ρ_b is soil bulk density (kg m⁻³ or Mg m⁻³), M_s is soil solid mass (kg or Mg), and V_t is ...