Few land management practices have the potential to
impact upon soil aeration as directly or rapidly as tillage.
Indeed, often, the reason for performing tillage is to modify
or improve soil physical properties including aeration. The
problems associated with inadequate aeration have been
comprehensively reviewed elsewhere (1, 2). Important
effects of limited soil aeration in crop production are:
altered nutrient dynamics, a shift from oxidative to
reductive chemical/biological reactions, impaired plant
growth, and changes in gas equilibria affecting both soil and
ambient atmospheres. For example, consider the soil
nitrogen cycle which aeration effects via its influence on
denitrification and gaseous nitrogen losses, decreased
nitrogen mineralization rate and a reduction in nodulation
and symbiotic fixation by leguminous plants (3). If the
oxygen supply is sufficiently limited, and anerobosis sets in,
then the products of reduction reactions may accumulate to
toxic levels. In addition, a depleted oxygen supply may
constrain root form and function, such as water and nutrient
uptake, and therefore plant shoot performance even when
many other soil physical factors are favorable (4).
Unfortunately, relatively short periods of oxygen shortage
can seriously compromise crop performance if they
coincide with critical stages of crop growth (1). Finally,
there are the effects of gas sources and sinks in the soil and
transformations of soil gaseous components, and the
exchange between soil and above ground air, on the
atmosphere, e.g., diminished soil aeration may enhance the
emission of greenhouse gases (5).
While the tillage-related literature is voluminous, little
of it directly addresses soil aeration. Of necessity, this
short article critiques only research which has measured
aeration status directly—particularly indices of concentration
and rate—and will make little or no attempt to draw
inferences about the effect of tillage on soil aeration from
studies reporting other related soil characteristics.
Although bulk density, moisture content, and pore size
distribution are related to soil aeration, and so may be
indicative of aeration status, their direct relevance to a
nuanced understanding of soil aeration is problematical.
For instance, measurements of pore space convey little
about pore continuity, tortuosity, or stability (6), whereas
these effects are largely integrated de facto in measurements
of oxygen diffusion rate (ODR)
