Abstract. This study focuses on soil physical aspects of soil
quality and health with the objective to define procedures with worldwide
rather than only regional applicability, reflecting modern developments in
soil physical and agronomic research and addressing important questions
regarding possible effects of soil degradation and climate change. In
contrast to water and air, soils cannot, even after much research, be
characterized by a universally accepted quality definition and this hampers
the internal and external communication process. Soil quality expresses the
capacity of the soil to function. Biomass production is a primary function,
next to filtering and organic matter accumulation, and can be modeled with
soil–water–atmosphere–plant (SWAP) simulation models, as used in the
agronomic yield-gap program that defines potential yields (Yp) for any
location on earth determined by radiation, temperature and standardized crop
characteristics, assuming adequate water and nutrient supply and lack of
pests and diseases. The water-limited yield (Yw) reflects, in addition, the
often limited water availability at a particular location. Actual yields
(Ya) can be considered in relation to Yw to indicate yield gaps, to be
expressed in terms of the indicator (Ya/Yw)×100.
Soil data to calculate Yw for a given soil type (the genoform) should
consist of a range of soil properties as a function of past management
(various phenoforms) rather than as a single representative dataset. This way
a Yw-based characteristic soil quality range for every soil type is
defined, based on semipermanent soil properties. In this study effects of
subsoil compaction, overland flow following surface compaction and erosion
were simulated for six soil series in the Destra Sele area
in Italy, including effects of climate change. Recent proposals consider soil
health, which appeals more to people than soil quality and is now defined by
separate soil physical, chemical and biological indicators. Focusing on the
soil function biomass production, physical soil health at a given time of a
given type of soil can be expressed as a point (defined by a measured Ya)
on the defined soil quality range for that particular type of soil, thereby
defining the seriousness of the problem and the scope for improvement. The
six soils showed different behavior following the three types of land
degradation and projected climate change up to the year 2100. Effects are
expected to be major as reductions of biomass production of up to 50 %
appear likely under the scenarios. Rather than consider soil physical,
chemical and biological indicators separately, as proposed now elsewhere for
soil health, a sequential procedure is discussed, logically linking the
separate procedures.
Defining a reference system for biological indicators of agricultural soil quality in Wallonia, Belgium
