Sustainable Soil Management Is More than What and How Crops Are Grown - Principles of Sustainable Soil Management in Agroecosystems - page 343

For these natural science writers as far back as 1945, tillage, regardless of type
and intensity, is not compatible with sustainable agriculture. We only have to look
at the various international assessments of the large-scale degradation of our land
resource base and the loss of productivity globally to reach a consensus as to whether
or not the further promotion of any form of tillage-based agriculture is a wise devel-
opment strategy. We contend that to continue with intensive tillage agriculture now
verges on irresponsibility toward society and nature. Thus, we maintain that with
tillage-based agriculture in all agroecologies, no matter how different and unsuitable
they may seem for no-till farming, crop productivity (efficiency) and output cannot
be optimized to the full potential. Further, agricultural land under tillage is not fully
able to deliver the needed range and quality of environmental services that are medi-
ated by ecosystem functions in the soil system. Obviously, something must change.
14.3.1 S oil D egraDation from an e cological P erSPective
Agricultural land is derived from natural forest, savanna, and grassland ecosystems
in which topsoil formation processes are driven by the natural bio-chemo-physical
environment. The attending ecosystem functions mediated by soil, terrain, climate,
and vegetation are driven by nature. Human-induced changes of the land by removing
original vegetation, tilling and cultivating, burning, introducing new species of plants
and animals, and adding agrochemicals are significant changes that can equal in their
effect to rare catastrophic changes during geological time that set off sequences of
erosion and reshaping of the topography. The altered hydrology, limited crop residue
input, and long periods when bare soil is exposed to effects of sun, wind, and rain are
the basic causes of land degradation. This has been the traditional view held by many
experts during much of the past century, which led to large-scale (though, as we now
see, insufficiently effective) soil conservation measures that were developed after the
North American “dust bowl” disaster in the 1930s. The first measures involved prac-
tices such as contour plowing, terracing, and/or strip cropping to reduce runoff and soil
erosion. However, they did not specifically target damage to soil aggregation, depletion
of SOM, and loss of porosity by pulverization and compaction—which are significant
factors in changing the balance between infiltration and runoff.
Tillage results in accelerated oxidation of carbon-rich organic matter by soil biota,
faster than it may be being replaced, leading to progressive depletion of carbon-rich
SOM. The common belief is that tillage accelerates crop residue breakdown, leading to
increase in soil biota and nutrient flushes when residue is mixed with soil. Any positive
effect is of very short duration and with little positive effect on soil quality and function.
Rapid breakdown of crop residues starves soil organisms of their future source of energy
for life processes, with consequent decline in their effectiveness in maintaining/improv-
ing the health and quality of the soil as a medium for plants' rooting and functioning.
14.3.2 a gricultural i ntenSification B aSeD on
the “i “interventioniSt” ” P araDigm
The post-WWII agricultural intensification placed increasing reliance upon breed-
ing “new” high yielding seeds and more intensive tillage of various types pulled by