By Njoku, Boniface Onogbo
~aboratory, greenhouse and field studies were carried out to
investigate the reeponse of Caesava (Manihot esculente Crane) to s o i l
acidity and liming i n two ultfsols of eastern Nigeria. Jt was obs&ved
that at pH 4.0-4.5 the mre acid-sensitive cassava cultivar TMS30211
,. . - .
produced maximum dry matter when the level of exchangeable A1 was
1,O rneqL100g provided the exchangeable Ca level was in the range of
0.7 to 1.0 meq/100g.
Two out of four cassava cultivars tested showed positive response
to low levels (1.0 to 2.0t/ha) of lime while the other two responded
negatively. The bas i s of tolerance t o s o i. l . a c idi ty was ascribed t o
the ability of the cassava cultivars to withstand low levels of s o i l . .. .
calcium. It was noted that euch cultivars were able to take up enough
Ca from Ca-deficient soils. On the other hand,. the response to liming
was essentially a response to Ca as a nutrient as the line level a t
which the response was obtained was not high enough to sufficiently -
reduce the level of exchangeable A1 or s o i l solution A l . Calcium . - . . . .
deficiency was, therefore, identified as the main factor limiting cassava
. . . .
growth in the acid soils tested. The implication of t h i s finding
, .. .
is that cement industry chimney dust and steel industry basic slag which
. - , . ,
have. hi. gh Ca content but r e l a t ive ly low neut ral izino value. can be used
. . . ' C : , + :; - , - ,, , ' , , - , ..
to amend acid soils rather than expensive conver
x i i .
Deep incorporation of lime which is widely reported to neutralize
subsoil Al and enhance crop yield was found to be effective in reducing .
the level of s o i l A1 but failed to improve the yield of cassava.
As a liming material, hydrated lime was shown not to have much
reafdual value in the high rainfalJ. sene terrted. Although a d 1 pH
and exchangeable Ca levels roee steadily while exchangeable A1 decreased
in the surface soil layer soon after lime application, there was a
tendency for the values to return to their pre-liming levels within 12
months of application due to high leaching and run-off losses of
bases. There is need, therefore, to apply small doses of lime but more
frequently and a t such a period that sufficient time is allowed for
soil-lime reaction to come to completion before the heavy rainstorms set
in.
The cassava cultivar TMS 30572 was identified as being highly
tolerant to soil acidity. It is high-yielding and its tubers have
good quality attributes. Cultivar u/41044 was found to be well adapted
to the ecological zone studied.
Liming had no effect on the reaction of the cassava cultivars to
green spider mite. Cassava cultivars TMS 30211 and U/41044 were found to be less susceptible to mite damage than TMS 3