Organic farming differs from conventional farming mainly in
tillage methods, crop rotations, fertilizer applications, and pest
control methods. Whereas conventional farming systems depend
on chemical fertilizers and pesticides, organic farming systems
avoid or largely exclude their use by relying upon crop rotations,
manuring, mechanical cultivation, organic fertilizers, and biological
pest control to maintain soil productivity, supply plant
nutrients, and control pests5•
We studied two adjacent winter wheat ( Triticum aestivum)
fields from two farms, one organically managed and the other
conventionally managed, containing a study area where all
soil-forming factors as described by Jenny6, except management,
were equal. The study area was made up of Naff silt loam
(fine-silty, mixed, mesic Ultic Argixeroll), a dark-coloured, welldrained
soil which formed under grass in deep deposits of loess
mixed with some thin layers of volcanic ash7• Typically, Naff
soils have a silt loam surface Al horizon 20-46 cm thick, overlying
an A2 or AB horizon of heavy silt loam. The next layer is
a strong, silty clay loam Bt or argillic B horizon (a layer of clay
accumulation that is significantly denser than the layer(s)
above). The slope of the study area was -6.5%, but ranged
from 5 to 8%.