Soil health in agricultural systems

Abstract

Soil health is presented as an integrative property that reflects the capacity of soil to respond to agricultural intervention, so that it continues to support both the agricultural production and the provision of other ecosystem services. The major challenge within sustainable soil management is to conserve ecosystem service delivery while optimizing agricultural yields. It is proposed that soil health is dependent on the maintenance of four major functions: carbon transformations; nutrient cycles; soil structure maintenance; and the regulation of pests and diseases. Each of these functions is manifested as an aggregate of a variety of biological processes provided by a diversity of interacting soil organisms under the influence of the abiotic soil environment. Analysis of current models of the soil community under the impact of agricultural interventions (particularly those entailing substitution of biological processes with fossil fuel-derived energy or inputs) confirms the highly integrative pattern of interactions within each of these functions and leads to the conclusion that measurement of individual groups of organisms, processes or soil properties does not suffice to indicate the state of the soil health. A further conclusion is that quantifying the flow of energy and carbon between functions is an essential but non-trivial task for the assessment and management of soil health.

Figure 1

Relationships between the activities of the soil biological community and a range of ecosystem goods and services that society might expect from agricultural soils. OM, organic matter; SOM, soil organic matter.

Figure 2

Major trophic relationships in the soil biological community of an agricultural soil under zero tillage (adapted with permission from Hendrix et al. (1986)).

Figure 3

Interconnectedness between the major ecosystem functions of soil. The arrows hypothesize two flows of energy from the plant to the major functions of the soil biota; either directly through the actions of herbivory, parasitism and mutualistic symbiosis, or indirectly via heterotrophic carbon-transforming processes in the soil. Soil organic matter (SOM) synthesis is pictured as supported by energy flowing from the decomposition of plant residues and contributing energy in its turn directly (i.e. by virtue of its properties) to soil structure maintenance and indirectly, through its own decomposition, to nutrient cycling and biological population regulation. See text for further explanation.

Figure 4

Performance curve showing an idealized relationship between input(s) to the soil system and delivery of an output of an ecosystem service. The capacity of the system is the output above which process performance deteriorates.

Figure 5

Differences in soil communities (shown in relation to their body size), carbon and nitrogen in mechanized versus no-tillage agriculture averaged for 106 studies across a variety of site conditions (adapted with permission from Wardle 1995). The index V is a measure of the abundance or mass of organisms under mechanized as compared with no-tillage; a value of zero implies equal abundance in each treatment, negative values indicate inhibition by mechanized tillage to a maximum of −1, i.e. the state in which the organisms only occur under no-till (see original paper for further details).