A good example of the need for a new environmentally driven
T-value is erosion from fields with high phosphorous values. P losses
are highly correlated with soil P levels; in regions with lots of
livestock, and in some regions like parts of Kentucky with naturally high
P soils, erosion needs to be lowered below 5 tons per acre (typically
T-value) to keep P loadings down into surface waters; and the need for
field edge sediment trapping practices/installations like filter strips
and sediment ponds is greatly heightened. There is extensive
literature on these needs.
No one has formerly proposed nor discussed in any great detail
the incorporation of disease suppressiveness into T-values. I do not
think such an attempt is a good idea, since it would entail mixing too
many concepts/properties of soil at once into one measure. The physical
state and quality of the soil -- top soil depth, bulk density/degree of
compaction, organic matter content,etc -- changes slowly over time and
can be thought of as the infrastructure of the soil within which various
chemical and biological cycles and processes unfold that determine
whether plants can grow in a healthful fashion, whether microorganisms
remain in a roughly healthy and balanced relationship with each other,
etc. Regardless of the physical state of the soil -- whether it was rich
to begin with, abused, or on the come-back trail -- there are steps a
farmer can take to fully exploit the capacity of the soil in its current
state to support microbial activity, hold and cycle nutrients, take in
and retain mositure, etc. For this reason, I think disease
suppressiveness should be viewed and studied as a property of soils that
warrants its own set of measures, concepts, and "H-values" -- a soil
health value.