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Research Article
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Soil Nutrient Status and Nutrient Interactions as Influenced by Agro Wastes and Mineral Fertilizer in an Incubation Study in the South West Nigeria |
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L.S. Ayeni
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E.O. Adeleye
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ABSTRACT
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The objective of this study was to compare the effects of NPK 20:10:10 fertilizer, cocoa pod ash and poultry manure on soil nutrient status as well as their interactions. The study was conducted in South Western Nigeria. Two levels of cocoa pod ash at 5 and 10 t ha-1; poultry manure at 5 and 10 t ha-l and NPK 20:10:10 fertilizer at 100 and 200 kg ha-l were separately mixed with soil constituents. There was a control without any treatment. The treatments were replicated nine times on completely randomized design and were sampled at 30, 60 and 90 days for analysis. Three samples per treatment were analysed and discarded each month. Cocoa pod ash and poultry manure rates significantly increased (p<0.05) soil pH, organic matter, N, Ca, Mg, CEC and percent base saturation. Cocoa pod ash at 10 t ha-1 recorded the highest pH and Ca at 30, 60 and 90 days. NPK fertilizer at 200 kg ha-1 had the highest N, P and exchangeable acidity at 30, 60 and 90 days. Cocoa pod ash applied at 10 t ha-1 had highest CEC at 60 days of incubation. Cocoa pod ash and poultry manure decreased exchangeable acidity, while NPK rates increased it. Cocoa pod ash at 10 t ha-1 had the widest Ca: Mg ratio among the treatments and thus may be prone to nutrient antagonism. Cocoa pod ash and poultry manure rates reduced K: Ca ratio compared with control. Among the treatments, OC: N, Ca: Mg and K: Ca ratios fall within the acceptable range for arable crop production in Southwestern Nigeria.
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INTRODUCTION
Chemical properties of soil play significant role in crop production. A soil
that supplies adequate Nitrogen (N), Phosphorus (P), Potassium (K), Calcium
(Ca), Magnesium (Mg), Sulphur (S) and micronutrients with favourable soil pH
will produce plant of vigour and good yield if other conditions of growth such
as biological and physical properties of soil are favourable (Anderson,1991).
Soils are not just to supply adequate nutrients alone but the nutrients to be
in proper balance. Phosphorus is known to help in root growth, seed formation
and quick ripening of fruits while Ca helps in pectate formation and tuberization
(Anonymous, 1993). Calcium may antagonize available
P if they are not in balanced proportion. Though, N helps in chlorophyll formation
and plant growth, its excess in relation to other nutrients, such as P, K and
S can delay crop maturity. Also, Na and K have negative interactions. Changes
in soil pH will result in numerous interactions where one ion or nutrient interferes
with or competes with the uptake and utilization of other nutrients by plants.
Studies have shown the effectiveness of cocoa pod ash, poultry manure and mineral
fertilizer in the release of nutrients for crop production in Southwestern Nigeria
(Ayeni et al., 2008; Ayeni,
2010; Akanni and Ojeniyi, 2007). Cocoa pod is derived
from Theobroma cacao popularly grown for its chocolate flavour. Its pod
husks are burnt purposely for the control of black pod disease. Its ash has
also been tested in farmers field as source of plant nutrients. About
800,000 metric tonnes of cocoa pod is found lying fallow in farmers field
in southwestern Nigeria (Egunjobi, 1975). Poultry manure
is also a cheap source of plant nutrients (Mbagwu, 1992;
Mba, 2006; Mbah and. Mbagwu, 2006).
Huge amount of poultry dung are found being dumped in urban cities of Nigeria
which constitutes health hazard. Its use as farm manure has helped to reduce
environmental pollution. Peasant farmers in Southwestern Nigeria have noted
the impact of mineral fertilizers on crop yields but have been using them without
soil test. It is necessary to study the rate at which NPK fertilizer, cocoa
pod ash and poultry manure release N, P, K Ca and Mg to the soil for crop production.
Hence, the objective of this study was to compare the effects of NPK 20:10:10
fertilizer, cocoa pod ash and poultry manure on soil nutrient status and some
other soil fertility variables.
MATERIALS AND METHODS
Soil and organic wastes analysis: Laboratory incubation study was carried
from March-May 2009 to determine the effects of NPK 20:10:10 fertilizer, cocoa
pod ash and poultry manure on soil nutrient status as well as their interactions
on Alfisol in southwestern Nigeria. Soil samples were collected from the field
at 0-20 cm depth, air-dried and sieved through 2 mm sieved mesh. Part of the
soil samples was used for routine soil analysis and the remaining soil sample
was used for laboratory incubation study.
The pH of the soil was determined in 2:1 CaCl2/soil suspension using
a glass electrode pH meter. Organic matter was determined by the Walkley
and Black (1934) dichromate oxidation method. The percentage organic matter
was calculated by multiplying the values of organic carbon by the conventional
Van Bemmeller factor of 1.724 based on the assumption that soil organic matter
contains 58% carbon (Allison, 1982). Total N was determined
by the Kjedahl method (Jackson, 1962). Available phosphorus
was extracted by 0.03 M NH4F+0.025 M HCl (Bray and Kurtz,
1945) and the P in the extractant was determined by colorimeter. Exchangeable
bases (Na, Ca, K and Mg) were extracted with 1 N ammonium acetate at pH 7.0.
Potassium and Na were read using flame photometer while Ca and Mg were determined
by Perkin Elmer 20 Atomic Absorption Spectrophotometer (AAS) (AOAC,
1990).
The exchangeable acidity was determined from 0.1 M KCl extracts and titrated
with 0.1 M HCl (Mclean, 1982). Effective Cation Exchange
Capacity (ECEC) was established as the summation of the exchangeable cations
(K, Ca, Mg and Na).
The nutrient composition of powdered poultry manure and cocoa husk ash were
also determined after ashing in the muffle furnace. Total N was determined by
Kjedahl method. For other nutrients, ground samples were subjected to wet digestion
using 25-5-5 mL of HNO3-H2SO4-HClO4
acids (AOAC, 1990). The filtrate was used for nutrients determination
as done in routine soil analysis. Total P was determined by colorimeter, K by
flame photometer and Ca, Mg and by AAS.
A laboratory incubation study to determine the interactions of cocoa pod ash, poultry manure and NPK 20:10:10 fertilizer with soil constituents at 90 days was conducted at Adeyemi College of Education and was later transferred to the Federal University of Technology for chemical analysis. One hundred grammes of soil sample in plastic cup were used for the incubation study. The treatments applied consisted of cocoa pod ash at 0, 0.25 and 0.5 g, poultry manure at 0, 0.25 and 0.5 g to represent 0, 5 and 10 t ha-1, respectively. NPK 20:10:10 fertilizer consisted of 0, 0.05 and 0.1 g to represent 0, 100 and 200 kg ha-1. The treatments were replicated three times. The soil samples were arranged on a flat platform in the laboratory in completely randomized design. The experiment was in the laboratory for 90 days. RESULTS
The soil used for the conduct of experiment was slightly acidic deficient in
OM, N and K (Table 1) considering the critical level of nutrients
recommended for arable crops in Southwestern Nigeria (Sobulo
and Osiname, 1987). Poultry manure had higher N and P than cocoa pod ash
while cocoa pod ash was higher in cations (Table 2).
Compared with control, cocoa pod ash and poultry manure rates significantly
increased (p<0.05) soil pH at 30 days of incubation (Table
3). Application of NPK 20:10:10 fertilizer had no significant effect on
soil pH at 30 days of incubation. Cocoa pod ash applied at 5t ha-1
significantly increased soil pH more than 10 t ha-1 poultry manure.
Also, 10 t ha-1 of cocoa pod ash significantly increased (p<0.05)
soil pH than 10 t ha-1 poultry manure. Among the treatments, 10 t
ha-1 cocoa pod ash recorded the highest pH while 200 kg ha-1
NPK 20:10:10 had the lowest soil pH at 30 days of incubation. Compared with
control, cocoa pod ash, poultry manure and NPK fertilizers rates significantly
increased (p<0.05) soil OM and N. NPK fertilizers applied at 200 kg ha-1
had the highest OM and N while the control experiment recorded the lowest OM
and N. all the treatments significantly increased soil P compared with control.
Table 2: |
Nutrient concentration of poultry manure and cocoa pod ash
(%) |
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Table 3: |
Effect of NPK 20:10:10 fertilizer, cocoa pod ash and poultry
manure on soil chemical properties 30 days after application |
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NPK: NPK 20:10:10 fertilizer, CPA: Cocoa pod ash, PM: Poultry
manure |
Poultry manure at 10 t ha-1 had higher P than 5 t ha-1
poultry manure. NPK 20:10:10 fertilizer applied at 200 kg ha-1 recorded
the highest P while 5 t ha-1 cocoa pod ash recorded the lowest P.
Poultry manure applied at 10 t ha-1 significantly increased soil
phosphorus compared with 10 t ha-1 of cocoa pod ash at 30 days of
incubation. All the treatments significantly increased K except 100 kg ha-1
NPK fertilizer compared with control.
Cocoa pod ash at 10 t ha-1 supplied more K than 5 t ha-1 cocoa pod ash; 5 t ha-1 cocoa pod ash had higher soil K than 5 t ha-1 poultry manure, 10 t ha-1 cocoa pod ash was higher in soil K than 10 t ha-1 poultry manure. Cocoa pod ash applied at 10 t ha-1 supplied the highest K while, 100 kg ha-1 NPK fertilizer and the control experiment recorded the lowest K. Cocoa pod ash applied at 10 t ha-1 significantly in creased soil Ca than 5 t ha-l cocoa pod ash and 10 t ha-l poultry manure. Cocoa pod ash applied at 10 t ha-l had highest Ca while 200 kg ha-l NPK fertilizer had the lowest Ca. poultry manure at 5 t ha-l had the highest Mg, while, 10 t ha-l cocoa pod as reduced Mg. All the treatments significantly increased Na except NPK fertilizer rates. Cocoa pod ash rates and poultry manure rates significantly reduced exchangeable acidity while NPK fertilizer rates had n significant effect at 30 days of incubation. At 30 days of incubation cocoa pod ash and poultry manure rates significantly increased soil Cation Exchange Capacity (CEC). Cocoa pod ash applied at 10 t ha-1 recorded the highest CEC while 200 kg ha-1 of NPK 20:10:10 had the lowest CEC. Compared with control cocoa pod ash rates and 5 t ha-l poultry manure significantly increased the ECEC of the soil cocoa pod ash at 10 t ha-l the highest ECEC while NPK fertilizer at 200 kg ha-1 had the lowest ECE.
At 60 days of incubation, all the treatments except NPK fertilizer rates significantly
increased (p<0.05) soil pH. Cocoa pod ash applied at 10 t ha-l
had highest soil NPK fertilizers at 200 kg ha-l had the lowest soil
pH rates (Table 4). Cocoa pod ash and poultry manure rates
significantly increased soil pH over NPK fertilizer rates and control. Only
poultry manure rates significantly increased soil organic matter and N at 60
days of incubation. Relative to control, all the treatments significantly increased
soil P. NPK fertilizer at 200 kg ha-l recorded the highest P followed
by 10 t ha-l poultry manure. At 60 days, 10 t ha-l poultry
manure significantly increased P over 5 t ha-l poultry manure. Compared
with control cocoa pod ash and poultry manure rates significantly increased
soil Ca. 10 t ha-l cocoa pod ash was significantly (p<o.05) higher
than 10 t ha-l poultry manure in Ca. 10 t ha-l cocoa pod
ash recorded the highest increase in Ca. Though increases in Mg was not significantly,
among the treatments, 5 t ha-l poultry manure recorded the highest
Mg while 10 t ha-l cocoa pod ash recorded the lowest Mg at 60 days
of incubation. Cocoa pod ash and poultry manure rates had significant effect
on soil Na compared with control.
Table 4: |
Effect of NPK 20:10:10 fertilizer, cocoa pod ash and poultry
manure on soil chemical properties 60 days after application |
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NPK: NPK 20:10:10 fertilizer, CPA: Cocoa pod ash, PM: Poultry
manure |
Table 5: |
Effect of NPK 20:10:10 fertilizer, cocoa pod ash and poultry
manure on soil chemical properties 90 days after application |
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NPK: NPK 20:10:10 fertilizer, CPA: Cocoa pod ash, PM: Poultry
manure |
Cocoa pod ash and poultry manure rates significantly reduced exchange acidity
compared with control. The NPK fertilizer at 200 kg ha-l had the
highest EA while poultry manure at 10 t ha-l had the lowest EA 60
days after incubation. Cocoa pod ash and poultry manure rates significantly
increased CEC compared with control. Poultry manure at 10 t ha-l
recorded the highest CEC while 100 kg ha-l had the lowest CEC. Also,
cocoa pod and poultry manure at all levels significantly increased ECEC except
5 t ha-l cocoa pod ash. Cocoa pod ash at 10 t ha-l had
the highest ECEC while 100 kg ha-l NPK fertilizer had the lowest
ECEC.
At 90 days of incubation, cocoa pod ash and poultry manure rates significantly increased soil pH (Table 5). The NPK fertilizer tended to reduce soil pH at 90 days of incubation. Cocoa pod ash at 10 t ha-l had more effect on soil pH than other treatments. Relative to control and NPK fertilizer, cocoa pod ash and poultry manure rates significantly increased (p<0.05) soil OM and N. All the treatments had higher P. At 90 days, Ca was more pronounced in soils treated with cocoa pod ash and poultry manure than NPK fertilizer rates and control. Cocoa pod ash applied at 10 t ha-l most enhanced soil Ca. cocoa pod ash and poultry manure rates seemed to reduce soil Mg at 90 days of incubation. All the treatments significantly increased soil Na except NPK fertilizer rates over control. Cocoa pod ash and poultry manure tended to reduce soil exchangeable acidity compared with control and NPK fertilizer compared with control, cocoa pod ash and poultry manure rates significantly increased CEC. Cocoa pod ash at 10 t ha-l recorded the highest CEC at 90 days of incubation. Cocoa pod ash at 10 t ha-l recorded the highest ECEC followed by poultry manure at 10 t ha-l.
The mean C/N ratio for 30, 60 and 90 days of incubation period showed 200 kg
ha-l NPK fertilizer with soil constituents recorded the lowest C/N
ratio while 10 t ha-l had the highest C/N ratio.
Table 6: |
Effects of NPK 20:10:10 fertilizer, cocoa pod ash and poultry
manure on some soil nutrient ratios |
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NPK: NPK 20:10:10 fertilizer, CPA: Cocoa pod ash, PM: Poultry
manure |
Control experiment had the highest K/Mg ratio while 10 t ha-l cocoa
pod had least K/Mg ratio (Table 6). Cocoa pod ash applied
at 10 t ha-l had the widest Mg/Ca ratio as against control which
was lowest among the treatments. Control experiment recorded the highest K/Ca
ration while cocoa pod ash at 10 t ha-l recorded the lowest K/Ca
ratio.
DISCUSSION
The low fertility status of the soil used for the experiment shows that the
soil needs fertilization. There were increases in the pH of the soils amended
with cocoa pod ash and poultry manure. Whalen et al.
(2000) have reported a similar effect on soil pH after application of animal
manure. The higher soil pH in cocoa pod ash and poultry manure amended soils
may have been partially although, not totally due to Ca contents as the rate
of increase in pH was proportional to increase in Ca Calcium carbonate and organic
acids in the agrowastes (cocoa pod ash poultry manure) may collectively butter
soil acidity (Whalen et al., 2000) and the hydrolysis
of Na released from exchange sites or solubilized from the agrowastes can also
increase soil pH. The decreases experienced in pH of the soils treated with
NPK 20:10:10 fertilizer might be due to the acidic nature of the mineral fertilizer.
The persistent increase in organic matter and N might be as a result of mineralization.
Incubation of NPK 20:10:10 fertilizer, cocoa pod ash and poultry manure amended
soils produced net increases in the mineral N pool, which suggests conditions
were favouable for microbial growth and their activities in soils. The continuous
increase in soil N and P by cocoa pod ash and poultry manure throughout the
incubation period showed that much of N and P added in the agrowastes remain
in a pool that is readily available for plant uptake and that mineralization
has not stopped at 90 days of incubation. The higher amount of N and P released
by NPK fertilizer over cocoa pod ash and poultry manure suggests that mineralization
was fasters in the mineral fertilizer than the agrowastes during the incubation
period. This might as a result of rapid solubility of NPK in soil solution.
Though, C/N ratio plays significant role in N and P mineralization, the rapid
mineralization of nutrients in soils fertilized with NPK 20:10:10 over the agrowastes
could not be adduced to C/N ratio because the C/N ratios of cocoa pod ash and
poultry manure still fall within the acceptable range for N and P mineralization.
Bernard et al. (2005) suggest that a C/N ratio
greater than 30 and a C/N ratio greater than 300 generally cause soil N and
P immobilization. For 5 t ha-l cocoa pod ash, N mineralization stopped
at 60 days while mineralization proceeded to 90 days with 10 t ha-1
cocoa pod ash. This suggests exhaustible release of N present in 5 t ha-l
cocoa pod ash. The gradual release of N and P by the organic wastes especially
at 10 t ha-l suggests that the N and P will not be easily prone to
leaching and will be more available to crops that have their vegetative and
reproductive cycle beyond 90 days. Split application of NPK fertilizers that
is being practiced by local farmers in Nigeria due to fear of nutrient leaching
may not be necessary if cocoa pod ash or poultry manure is used as fertilizer
since the nutrients are gradually being released.
The higher K/Ca, Na and Mg recorded by organic wastes over NPK fertilizer suggests
the superiority of cocoa pod ash and poultry manure in supplying cations (except
K) to the soil which acts as liming materials that is not included in NPK 20:10:10
formulation. The reduction in Exchangeable Acidity (EA) in soils amended with
agrowastes and the consequent increase in EA in soils fertilized with NPK 20:10:10
in this experiment suggests the ability of these organic wastes in lowering
soil Al3+ and H2+ concentration. Cocoa pod ash released
more K and Ca to soil than poultry manure. This is expected because the chemical
composition of cocoa pod ash shows that it contains more K and Ca than poultry
manure. The higher release of K and Ca by cocoa pod ash suggests that it will
be more useful in correcting soil acidity than poultry manure if judiciously
applied. Both cocoa pod ash and poultry manure especially at 10 t ha-1
supplied adequate K, Ca and Mg for plant use (Sobulo, 1990).
Therefore, these cations will not constitute a yield limiting factor if these
agrowastes are properly applied to give positive interactions. An interaction
occurs when the level of one production factor influences the response of other
factors. A positive interaction occurs when the influence of the combined practices
exceeds the sum of the influences of the individual practices (Anonymous,
1993).
Cocoa pod ash and poultry manure Ca/Mg ratios fall within the acceptable range
1:30 (Adepetu et al., 1979) with which soil condition
is usually not expected to produce Mg deficiency in plants. Adetunji
(1991) suggests a Ca/Mg ratio of 1:2 as the best soil condition that will
not produce Mg deficiency in plants. According to Adetunji
(1991) assertion, 10t ha-1 cocoa pod ash (Ca/Mg, 1:7) may cause
Mg deficiency as the Mg released was too low compared with other treatments.
Ayeni (2009) in South Western Nigeria noted higher yield
of maize in soils amended with 5 t ha-1 cocoa pod ash than its corresponding
10 t ha-1, he attributed it to nutrient imbalance in South Western
Nigeria. Potassium is known to antagonize Ca. Cocoa pod ash and poultry manure
were able to reduce K/Ca ratio when they were mixed with soil constituents in
this experiment. It is also noted that K/Ca ratio was substantially decreased
when 200 g ha-1 NPK fertilizer was added to the soil as against high
K/Ca ratio in control experiment and 100 g ha-1 NPK fertilizer. This
shows that the soil needs additional potassium fertilizer to reduce the K/Ca
ratio to make the nutrients balance for plant uptake.
Cocoa pod ash applied at 10 t ha-1 recorded the highest CEC especially
at 90 days of incubation. The CEC, though low, is not usual for highly weathered
tropical soils with relatively low content organic matter (Sobulo,
1990). The higher CEC recorded by the treatments over the control indicates
that cocoa pod ash, poultry manure and NPK fertilizer can improve fertility
status of the soil.
Cocoa pod ash and poultry manure had higher percent base saturation (%BS) than
the control and NPK fertilizer. Generally, initial soil characteristics and
control experiment showed that the %BS of the soil was greater than 50%. High
base status like this soil, is almost synonymous with high native soil fertility
and relatively low cost of supplying additional nutrients. Cocoa pod ash and
poultry manure in this research had significantly increased the %BS of the soil.
Sanchez and Salians (1981) have suggested that tropical
soils of this nature should be managed with the aim of maximizing the potential
of high yielding crop varieties and improving the cropping system with intensive
fertilizer input. Cocoa pod ash and poultry manure at high rates were able to
supply adequate plant nutrients in this experiment.
Soil Exchangeable Acidity (EA) was low in soils amended with cocoa pod ash
and poultry manure. The most important growth-limiting factor in acid soils
is believed to be Al toxicity because high levels of soluble and or exchangeable
Al combined with low level of Ca impair plant root development and limit water
and nutrient uptake by plants (Foy,1992; Rout
et al., 2000). The negative effects of these agro wastes on EA will
help to release nutrients such as P that have formed complex with Al if the
pH is properly monitored.
CONCLUSION The laboratory incubation study to compare the effect of coca pod ash, poultry manure and NPK 20:10:10 fertilizer on some soil chemical properties was conducted in South Western Nigeria indicated that cocoa pod ash and poultry manure rates significantly increased soil pH, organic OM, N, Ca, Mg, CEC and percent base saturation compared with control, NPK fertilizer rates reduced soil pH. Cocoa pod ash at 10 t ha-1 recorded the highest pH and Ca at 30, 60 and 90 days. The NPK fertilizer at 200 kg ha-1 had the highest N, P and exchangeable acidity at 30, 60 and 90 days. Cocoa pod ash applied at 10 t ha-1 had highest CEC at 60 days of incubation. Cocoa pod ash and poultry manure decreased exchangeable acidity while NPK rates increased it. Cocoa pod ash at 10 t ha-1 had the widest Ca: Mg ratio among the treatments and thus may be prone to nutrient antagonism. Cocoa pod ash and poultry manure rates reduced K: Ca ratio compared with control. Among the treatments, OC: N, Ca: Mg and K: Ca ratios fall within the acceptable range for arable crop production in Southwestern Nigeria. Also, cocoa pod ash and poultry manure at 10 t ha-1 rates supplied adequate OM, N, P, K, Ca and Mg. Poultry manure and cocoa pod ash could be used to fertilize soil for crop production.
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