Nutrient Management for Maize Production in Soils of the Savannah Zone of South-Western Nigeria
Olufemi Julius Ayodele
Solomon Olusegun Omotoso
Farmers would adopt fertilizer recommendations that
are based on soil fertility information in order to realize the potentials
for high maize yields offer by features of the savannah zone. Surface
(0-15 cm) samples of soil formed on basement complex rocks in the derived
and guinea savannah zone of south-western Nigeria were analysed and nutrient
status evaluated in relation to established critical levels. Sample of
four commonest soil series used to evaluate response to addition of single
nutrient: 100 mg N, 25 mg P, 20 mg Mg, 5 mg Fe, 5 mg Zn and 2.5 mg Cu
L-1 using dry weight of maize grown for weeks in greenhouse
pot studies. Maize grain yield responses to treatments that consisted
of N, P, K, NP, NK, PK, NPK, NPKMg, NPKMgFeCuZn and unfertilized control
were studied in four sites. The second field study in eight sites involved
comparison of maize grain yield obtained from two treatments: + and -
respective nutrients. The results indicated that soils are slightly acid
to neutral sands and loams with very low to high organic matter and total
N, low to medium exchangeable cations, low available P, Cu and Zn while
Mn and Fe are high. The order of maize response was N, Mg followed by
K, Zn and P in the greenhouse, single application of N fertilizer gave
high response while responses to P and K were low where soils exceeded
respective established critical nutrient levels. Yield response were enhanced
with fertilizer combinations that contained N, P and Mg. The primary needs
are N, P and Mg fertilizer soon after opening up the land for cultivation
from short fallows. After year of continuous cropping, K is needed while
addition of Cu and Zn would produce higher yields on plots that received
NPK fertilizers. The higher correlations with nutrient show that management
recommendation must emphasize the need to raise and maintain soil organic
matter levels, to ensure nutrient availability and increase response to
Savannah vegetation, consisting largely of perennial mesophytic grasses,
at least 80 cm in height, covers almost 80% of the land area in Nigeria.
The savannah zone in south-western Nigeria, is located between latitude
7 °-9 ° 30`N and consists of vegetation variants referred to as
derived savannah (forest-savannah mosaic, southern and northern guinea
savannah. The extent and floristic composition are being continuously
altered by slash- and burn bush-fallow cultivation, grazing and annual
(dry season) burning. The climate is fairly uniform tropical humid and
hot with a marked dry season which lasts from October/November to March/April
and so fall within the sub humid agro-ecological zone Annual rainfall
ranges between 1120 to 1350 mm with a bimodal distribution that allows
for two maize crops between March-July and August-November, The area consists
of tropical ferruginous soils, with sandy surface layer, low organic matter
content loe exchangeable bases. The soils have been classified as Luvisols,
Arenosols, Cambisols, Lithosols and Fluvisols which correspond to Alfisols,
Entisols and inceptisols with ustic moisture regimes and isohyperthermic
(FDALR, 1990). The clay fraction consists of kaolinite quartz, mica, sesquioxides
and montmorillonite chlorite or vermiculite-chlorite intergrades Murdoch
et al. (1976). The preponderance of non-swelling, 1:1 lattice low-activity
clays (Juo, 1980), with low specific surface reflects in equally low water
holding capacity of the soils. Thus, rapid infiltration and saturation
of the surface layer cause nutrient leaching losses, run-off and soil
erosion. Besides, water loss by evaporation from the sandy topsoils creates
droughty conditions between rainy periods (Jones and Wild, 1975).
Hand-hoe traditional subsistence farming is the dominant form of agriculture.
The grass-dominated vegetation is easily cleared, especially b bush burning.
Food crops are grown in various intercropping and interplanting systems
on land tilled with hoes, to make mounds, heaps or ridges. Low density
and small to medium size of woody tree species make the savannah suitable
for mechanized farming projects, as land development would involve low
capital investment. The climatic features, notably of bimodal rainfall
distribution, sunshine and temperature and the undulating topography.
Efficient fertilizer use, based on recommendations from soil testing
that recognizes inherent variability in soil properties is the tool for
realizing these potentials. The recommendations would differ from the
blanket rates made over large geographical areas which farmers are being
encouraged to adopt. Moreover, recent studies have shown the inappropriateness
of these blanket recommendations, being wasteful and causing yield reductions
when used continuously (FMANR, 1990). The status of nutrients, to identify
areas of deficiencies is vital to making soil fertility management recommendations.
This study presents data on the nutrient fertility status of soil in the
derived and guinea savannah zones of South-Western Nigeria, formed on
basement complex rocks, the nature of responses to applied nutrients and
the implications for efficient fertilizer management practices.
MATERIALS AND METHODS
Soil and Analytical Methods
Five hundred and forty surface (0-15 cm) soil samples were collected
from the area covered by derived and guinea savannah vegetation in South-Western
Nigeria. The soils are derived from igneous and metamorphic rocks of the
pre-Cambrian basement complex. The samples were air-dried, sieved (<2
mm) and analyzed for pH (in distilled water); particle size distribution;
organic matter and total N; exchangeable bases and total acidity, Effective
Cation Exchange Capacity (ECEC) and % base saturation; available P, Fe,
Cu, Zn and Mn using the recommended procedures described in IITA (1979).
Four of the commonest soil series were used for the studies. Four
hundred milliliter of soil samples were measured into half-litre plastic
cups; 100 mg N, 25 mg P, 20 mg Mg, 5 mg Fe, 2.5 mg Cu and 5 mg Zn-1
was added singly in solution form and the soils watered to near field
capacity. Maize was sown and thinned to five seedlings per cup after emergence.
The plants were watered daily, being careful to avoid water logging, The
top growth of four weeks old plants was harvested by cutting at soil surface
level, oven-dried, at 80 °C for 72 h and weighed.
Simple unreplicated plots, in which each treatment row, 20 m long,
was separated from the other by unfertilized treatment rows, were used
in two field experiments. Maize was sown on ploughed and harrowed land
at a spacing of 75x25 cm and later thinned to one seedling hill-1
to attain a population of 53,330 plants ha-1 in four sites.
The treatments consisted of N, P, K, NP, NK, PK, NPK, N P K Mg, NPKMgFeCuZn
and unfertilized control. The nutrients were applied at 120 kg N, 50 kg
P2O5, 60 kg K2O, 20 kg MgO, 2.5 kg Cu,
3 kg Fe and 5 kg Zn ha-1 using urea (46% N), single superphosphate
(SSP, 18% P2O5), muriate of potash (KCI or MOP,
60% K2O) and the sulphates of Mg, Fe, Cu and Zn. Urea was split-applied;
two-thirds mixed with the respective nutrient carriers in each treatment,
banded in 5 cm grooves, 8 cm away from the seed row at planting (basal)
and covered with soil and the remaining top dressed at about tasselling.
Eight sites were used for the second experiment involving two treatments:
+ and a particular nutrient, for yield to be compared with that
in which a complete combination of all the nutrients was applied. The
number of plants, number of cobs and weight of dehusked cobs were recorded
at harvest. The cobs were shelled and weight of grains taken. Grain moisture
was determined and yield adjusted to 15% moisture content.
RESULTS AND DISCUSSION
Soil Characteristics and Nutrient Status
The means and ranges of soil properties are shown in Table
1. In evaluating the fertility status, the data were compared with
critical soil nutrient levels established for maize in South-Western Nigeria
(Table 2) Few of the soils have acidity problem, (pH
<5.0) while 75% are in the low acidity range (pH 6.0-6.9). The soils
are, therefore, slightly acid to neutral and so, ideal for most arable
crops. The coarse texture (loams to sands) is typical of the surface horizon
of soils derived from crystalline basement complex rocks (Jones and Wild,
1975; Murdoch et al., 1976).
The low means organic matter 1.8%, compares with 1.3-1.8% reported as
average for soils of the savannah zone in South-Western Nigeria (FMANR,
1990). Over 80% of the soils contain <3% organic matter, a level above
which maize would not respond to N and P application. Mean total N, is
low (0.11%) compared with the established 0.15% critical level for maize
such that 70% of the soils are deficient. Maize is a high N-demanding
crop in which N deficiency readily shows up when soils contain less than
1% organic matter Sobulo and Osiname (1985). Thus, high maize yield would
not be supported, due to severe deficiency expected in >35% of the
soils which contain very low (<1.0%) organic matter. Annual dry season
burning and slash - and - burn land clearing practices cause complete
oxidation of litter and humified organic materials, with loss of N as
oxides into the atmosphere (Jones and Wild, 1975; FMANR, 1990).
Mean available P at (11.4 mg kg-1 soil) exceeds the critical
value of 8.5 mg kg-1 soil suggested for the soils in the derived
savannah and places the soils in the medium P fertility class base on
the soil test criteria and fertility map developed for Nigeria (FMANR,
1990). Nevertheless only 12% of the soils would probably not show response
to P application. There is presently no criterion for the interpretion
of effective CEC but the low values, which average 6.3 cmol kg-1
soil, reflect the high degree of weathering and leaching associated with
soil forming processes (Kang et al., 1991). The dominant cation
is Ca, though the value of less than 4.0 cmol kg-1 was found
in >60% of the soils. The suggested 1.5-2.0 cmol kg-1 soil
as critical level means that ca supply should not limit crop production.
With 0.16 and 0.28 cmol kg-1 as critical exchangeable K and
Mg, respectively, >20% of the soils would probably respond to K application
while only 10% of the soils are deficient in Mg. The 94% mean base saturation
stresses the fact that need for liming is not crucial to high crop yield
in the soils. The established critical levels for micronutrients imply
that Mn and Fe deficiencies may not occur while only 30 and 40% of the
soils are within the sufficiency range for available Zn and Cu, respectively.
Responses to Nutrient Applications
The respective single nutrients gave higher dry matter yields of maize
than the control treatment in the greenhouse, with N and Mg as the best
followed by K, Zn and P (Fig. 1). Response to N could
be attributed to low organic matter and total N levels in the soil unlike
addition of K and Mg which despite the high content, increased dry matter
yields. The order of increase in yield with micronutrients is: Zn>
Fe> Cu. Maize grain yields from single and combined nutrients, expressed
as percentage (%) of NPK treatment are shown in Fig. 2.
The low percentage yield of the control treatment shows that there was
significant response to fertilizer. Response to N was greater than control,
P and K treatments. Single P and K application compared to the control
at Ikare and Ogbomoso which had 0.20, 0.17 cmol kg-1 soil exchangeable
K and 31, 18 mg kg-1 soil available P, respectively. These
values were higher than critical levels established for maize in the soil
of the savannah zone (Agboola and Ayodele, 1985; Sobulo and Osiname, 1985;
FMANR, 1990). When the fertilizer combination contained N, yield responses
further increased, indicating its primary need, followed by P while K
was next only at Ogbomoso. Thus, the recommendation of a fertilizer mixture
that contains N, P and K is in order for maize. The inclusion of Mg and
micronutrients should further increase grain yields.
|| Means and ranges of nutrient status in surface soils
of the savannah in South Western Nigeria
|*: Effective CEC = Sum of exchangeable cations and exchangeable
acidity. L = Loam, LS = Loamy sand, S = Sand
|| Criteria for soil test interpretation and soil fertility
classes in South Western Nigeria
|Source: Agboola and Ayodele (1985), FMANR (1990)
The percentage yield using the minus-one nutrient technique is shown
in Table 3. Its interpretation, as follows: <50,
51-75, 76-88, 89-95 and >95% for very high, high, moderate, low and
no response, respectively, confirms the primary need of N, followed by
P. The response to P was low, even as P would not be recommended for Ikare
and Osogbo sites. Response to K was high at Osun and moderate at Ikole
and Ogbomoso. Response to Mg was high at Ikare and Iwo, but low at Osun
and Ogbomoso. The response despite high exchangeable Mg in the sites suggests
that the index of availability is probably inadequate and needs re-evaluation
(Agboola et al., 1976). Response to Mg depends on the ratios with
Ca and K, being low at Ca/Mg ≤5:1 but assured at K/Mg ratio greater
than 1:10. The Ca/Mg and K/Mg ratios varied between 1-2 and 4-12, respectively
in these soils and so indicate the possibility of responses to Mg. A critical
K/Mg ratio of 2.0 was suggested by Lombin and Fayemi (1977) and that even
at high levels in the soil, Mg uptake can be suppressed by high exchangeable
K status. Ilora, Omuo and Osun, with history of continuous cultivation
and use of blanket NPK compound fertilizer required Zn while Osun and
Iwo needed application of Cu.
|| Dry matter yield of maize in derived savannah soils
as influenced by nutrient additions
Implications for Nutrient Management and Sustainable Maize Production
Appropriate solutions to identified soil physical and chemical constraints,
in any farm, must be components of the improved management recommendations
for sustainable arable crop production.
||Effect of single and combine fertilizers on yield of
maize expressed relative to yield of NPK treatment
|| Percentage yield increase of maize in minus-one nutrient
Thus, the nature of variability in soil properties, notably nutrient
fertility status and crop responses to levels of management are issues
for consideration in assessing these soils formed on basement complex
rocks in the savannah zone of South-Western Nigeria for sustainable maize
The coarse texture of the topsoil, due to low clay content and dominance
of lACs make the soils to lose physical quality and become compacted under
continuous mechanized tillage practices (Lal et al., 1986). The
undesirable consequences: rapid internal drainage and heat transfer, rise
in soil and air temperatures, soil loss through runoff and erosion, nutrient
leaching losses, etc become more intense under compaction. The low clay
contributes minimally to nutrient availability compared to soil organic
matter, whose roles as the main source of nutrient supply and provision
of cation exchange sites are explained by the higher correlation coefficients
Fallows use natural processes to restore soil fertility, through organic
matter build-up and nutrient cycling between vegetation and the surface
layer of soil, such that during the cultivation phase, crop performance
depends on nutrient reserves and the rate of organic matter mineralization.
This is quite relevant to N and P availability whose major forms in soils
are as the organic fraction (Osiname, 1979). Thus, with average 0.11%
total N in these soils and assuming the 4% mineralization rate estimated
for cultivated soils in the savannah Jones and Wild (1975) much less than
120 kg N ha-1 recommended for high maize yields is released,
necessitating supplemental N from appropriate sources. Available P released
at this mineralization rate can be substantial; to reduce P fertilizer
requirements. Since P fixation is low, deficiency can be readily corrected.
As a result, maize responses have been to low P rates in several locations
of the derived savannah (Osiname, 1979; Ayodele, 1987). The organic matter
built up during fallows is reduced by mechanized land clearing and tillage,
intensive cultivation, continuous N application at high rates and shortening
of fallow lengths FMANR (1990). Thus, sustainable maize production must
emphasize some form of fallow given the low level of integrated crop-livestock
production in the zone, which should have ensured addition of animal manures
to the farms. The potentials of in-situ and live mulches, no tillage (zero
or reduced) and alley cropping systems, in which plant residues or hedgerow
pruning are returned as manures for nutrient recycling and soil cover
(Kang et al., 1990) need to be exploited.
Exchangeable K is high due to the nature of parent rocks-basement complex
rocks rich in K bearing minerals and large quantities of ashes, deposited
on the soil surface during slash and burn cultivation practices, as sources
of soluble K. However, since K uptake increases with N and P fertilization
and soluble K is lost through leaching, surface run-off and erosion, the
addition of K is necessary, especially under continuous cropping.
The inclusion of Mg and micronutrients would correct deficiencies that
show up under intensive cultivation and continuous use of NPK fertilizers,
to increase maize yields. For Cu and Zn, the levels are low but P build
up is possible to induce Zn deficiency. Available Fe is high while the
conditions for deficiency low pH in sandy soils and slightly acid to neutral
soils with high Cu, Zn and P (Kang et al., 1977), are not typical
of the zone. Where burning accompanies then cultivation practices, increase
in soil pH from deposited ashes would reduce Fe availability to cause
deficiency in upland rice (Vose, 1982). Conventional NPK fertilizer procured
for agricultural use is inadequate for sustainable maize production. Once
the land, opened from fallow, is cultivated for more than two to four
years and in soils with less than 3% organic matter, the need to include
Mg and micronutrients in the fertilizer schedule becomes essential for
high maize yields in the savannah zone of South-Western Nigeria.
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