Vn. Bushamuka et Rw. Zobel, MAIZE AND SOYBEAN TAP, BASAL, AND LATERAL ROOT RESPONSES TO A STRATIFIED ACID, ALUMINUM-TOXIC SOIL, Crop science, 38(2), 1998, pp. 416-421
Although crop seedling root systems are made up of several types of ro
ot (e.g., tap, basal, and lateral roots) there has been little attempt
to determine their respective sensitivity to abiotic stresses. Most a
cidic agricultural fields are treated so that they are only slightly o
r non-Al-toxic in the topsoil with Al-toxicity in the subsoil-effectiv
ely stratifying the soil profile relative to Al-toxicity. To determine
if there is differential root type sensitivity to Al-toxic soils, sev
eral maize (Zea mays L.) and soybean [Glycine mar (L.) Merr.] cultivar
s reported to be Al-tolerant, or sensitive, were grown in containers w
ith a stratified soil. This assembled soil consisted of a non-Al-toxic
, 100-mm-deep top layer and a 200-mm-deep Al-toxic bottom layer of Por
ter soil, a coarse-loamy, mixed, mesic Umbric Dystrochrepts, pH 4.5 an
d 92% Al saturation. Containers, backed with X-ray film, were exposed
to a neutron beam to determine tap, basal, and lateral root lengths in
both layers. Root lengths, relative to a limed control for each culti
var, in the Al-toxic bottom layer suggest that the tap, basal, and lat
eral roots of maize cv. CMS-36 are each Al-tolerant. The other ''toler
ant'' maize and soybean cultivars had only one or two root types toler
ant with the remaining root type(s), and all root types on the sensiti
ve cultivars, showing no growth in the Al-toxic bottom layer. Only two
cultivars, maize cv. SA-6 and soybean cv. Ferry, increased lateral ro
ot production in the non-toxic top layer, a classic avoidance response
. This variation in root type response to an AI-toxic bottom layer obs
erved among the previously identified Al-tolerant cultivars emphasizes
the importance of considering different root types as distinct entiti
es in studies of root function.