Irrigation-induced erosion and land leveling have decreased crop
yields on approximately 800 000 ha of south-central Idaho silt loam
soils. Previous attempts to increase subsoil productivity to that of
the topsoil have not been successful on these soils. This study was
conducted to find a method(s) for increasing the productivity of freshly
exposed subsoil to that of the topsoil and to determine the factor(s)
limiting subsoil production. A 4-yr study was initiated by removing
the surface 0.3 m of topsoil from strips between undisturbed topsoil
strips of a Portneuf silt loam (coarse-silty, mixed, mesic Durixerollic
Calciorthid). Different crop rotations were established within the
strips and fertility treatments were applied across the strips. The
fertilizer treatments were conventional fertilizer application according
to soil test, dairy manure, and two cottage cheese (acid) whey rates.
During the fourth year, dry edible bean (Phaseolus vulgaris L., cv.
Viva) were grown on the entire plot area as a test crop. The application
of 44 Mg manure ha-1 in the spring and 93 Mg manure ha-1 in the
fall of 1991 (first year of study) was the only treatment that restored
subsoil bean production to that of the topsoil plots. Plant Zn and
soil organic C concentrations were the only measured factors that
correlated with bean yield increases on the subsoil
