Increasing demands for food and other socio-economic crops
have intensified the quest for higher yields of crops. The low fertility of
soils is a hindrance to sustained agricultural productivity in Nigeria. Thus,
the use of lime and fertilizers remains critical for soil improvement and
increases in crop yields (Asadu et al., 2012).
Liming is an important strategy in the management of acidic
soils. In using it to increase the pH of acid soils and to eliminate the
deleterious effects of high concentrations of micronutrients farmers also
indirectly supply the nutrients Ca and Mg which are contained in the lime. The
degree to which a given amount of lime per unit of soil (volume) will increase
soil pH depends on soil properties such as the clay and organic matter contents
and the cation exchange capacity (CEC) of the soil. Soils with low CEC will
show a more marked pH increase than soils with high CEC (Turner, R. C. and C. Cleark,
J. S., 1996).
Acidity in the soil is usually controlled by the application
of amendments that have basic ions for easy neutralization of H+ and Al3+. The
most common amendments for effective increase of soil pH are limestone (CaCO3)
and dolomite [CaMg(CO3)2]. Other suggested liming materials include, palm bunch
refuse (PBR), wood ash, industrial lime and oyster shells (Brady et al., 2002).
Apart from reducing acidity, liming also increases the availability of several
plant nutrients and enhances the activity of soil micro organisms which
function in the release of phosphorus and sulphur from soil organic matter
In recent years, attention has shifted from dependence or
inorganic liming materials to inclusion of organic ones. Materials such as PBR
and wood ash are known to be rich in Ca. Mg and K, and thus can be effective as
Obighesan (1983) and IITA/NENRI (1999) summarized several
field experiments on the nutritional requirements of yam in different
agro-ecological zones of Nigeria. Their report indicated that yams performed
best in soils of low acidity that are also rich in K and Ca. other tuber crops
equally perform better when acidity is low and the basic materials high.
In South Eastern Nigeria soils derived from coastal plain
sand parent material are highly weathered, coarse textured in the surface
horizon, and of low contents of organic matter, nitrogen and exchangeable
bases. They may be low or high in content of available phosphorus. Being highly
leached, due to much rainfall, the soils are strongly acid and therefore
require both liming and fertilization (Ogban et al., 1998). Reports on specific
studies to determine optimum rates for combined or integrated applications of
both a liming material and a fertilizer are scarce. The purpose of this study
is to assess which combinations of an organic liming material (palm bunch
refuse, PBR) and a fertilizer such as NPK15:15:15 improved soil conditions the
most in support of higher yields of yam (Dioscorea rotundata).
(1) To assess the effects of palm bunch refuse (PBR),
NPK15:15:15 (NPK) and PBR+NPK combination on selected soil properties.
(2) To evaluate the potentials of PBR as a liming material.
(3) To assess the effects of sole and combined applications
of the two materials on the tuber yield of yam on this type of soil.