INTRODUCTION
Organic resources acting as soil amendments are
becoming increasingly utilized as soil fertility improvers over recent
years in tropical agriculture. In the sub Saharan tropical Africa, soil
productivity maintenance remains a knotty issue due to poor cultural practices
and fragile nature of most arable soils (Lloyd and Anthony, 1999; Oyetunji
et al., 2001). Bationo et al. (2006) described soil fertility
depletion as the single most important constraint to food security in
West Africa. Though use of organic resources such as animal manure, crop
residues and farmyard compost have been in use since earliest times for
improving soil fertility (Sridhar and Adeoye, 2003) and more recently
use of inorganic fertilizers, varying constraints still make the use of
these traditional non conventional and conventional methods of soil fertility
improvement inadequate to meet the challenges of soil fertility depletion
in the region. Such constraints include high procurement cost for mineral
fertilizer sources in sufficient quantities to meet farmers` needs especially
in resource poor countries and relatively low nutritive contents of traditional
crop residues/animal manure used for soil improvement.
The use of non traditional organic resources such as
weeds for soil fertility improvement purposes has been studied by Sonke
(1997), Gachengo (1996), Jama et al. (2000), Nziguheba et al.
(2002) and Chukwuka and Omotayo (2008) and these studies have established
the high potential of these resources in improving nutrient status and
subsequent crop yield in soils amended by these resources.
The objectives of this present investigation are to:
| • |
Assess the overall potential/impact of these two non traditional
organic resources, Tithonia diversifolia (tree marigold) and
Eichhornia crassipes (water hyacinth) on nutrient status of
depleted experimental soil samples. |
| • |
Evaluate nutrient uptake patterns of Zea mays L. in a nutrient
depleted soil amended with these organic residues. |
MATERIALS AND METHODS
Collection of Soil Samples
The study was conducted in the year 2007 commencing February up to
October of the same year. Two different soil profiles of an Alfisol [Arenic
Kandiudalf] (Soil Survey Staff, 2003) of top and sub soil samples were
collected from the Teaching and Research Farm, University of Ibadan, Ibadan-
Nigeria. Top soil samples were collected from a depth of 0-30 cm, while
subsoil samples were taken from depths of 45-60 cm, respectively.
Experimental Design and Treatments
The experimental design was a Complete Randomized Design (CRD) with
three replications for all treatments applied in both top and subsoil
samples. Equal weights (8 kg) of soil samples were measured in designated
labeled pots (10 L plastic buckets) which had been perforated at their
bases. Pots were labeled A-F. Fresh green leaves and tender stems of freshly
collected Tithonia biomass and also Chinese heap method prepared
water hyacinth compost (Basak, 1948) were applied to designated soils
in labeled buckets in sole and varying combinations applied as follows:
| A |
= Tithonia green manure alone (1 kg) |
| B |
= Water hyacinth compost alone (1 kg) |
| C |
= Tithonia green manure + Water hyacinth compost (0.5: 0.5
kg) |
| D |
= Tithonia green manure + Water hyacinth compost (0.25: 0.75
kg) |
| E |
= Tithonia green manure + Water hyacinth compost (0.75:0.25
kg) |
| F |
= Control (no fertilizer application) |
The organic soil amendments were incorporated into soils
in labeled pots for all designated treatments and allowed to mineralize
in soil for a period of 7 weeks. Early Yellow maize seeds (var. TZE COMP.
5-Y) obtained from the International Institute of Tropical Agriculture
(IITA), Ibadan-Nigeria were used in the study. Three seeds were sown per
pot representing experimental units. Seeds germinated 3-4 days after planting
and were thinned to one plant per pot seven days after emergence (7 DAE).
Normal atmospheric precipitation served as water source to the growing
seedlings since the experiment was performed during the rainy season.
Weather Conditions, Measurement of Plant Parameters and Harvest
The maize seeds were grown from July to October 2007 under atmospheric
conditions with maximum and minimum temperature values of 32 and 23 °C,
respectively with relative humidity value of 73% within the study period.
Annual rainfall range was between 1,300 and 1,500 mm (NIMET, 2007). Throughout
the growing season of about 12 weeks, growth responses and nutrient accumulation
of early yellow maize variety was assessed by measuring plant growth parameters.
These parameters include leaf length, leaf width, stem girth and plant
height were recorded from seven days after emergence (7 DAE) and was measured
and noted on weekly basis.
The maize cobs and residues (stover) were harvested after
the growing period of 12 weeks (12 WAP) and weighed individually to determine
their fresh weight for each plant sample. Cobs were then oven dried at
50 °C for a period of seventy-two hours and their dried weights were
also recorded. Total biomass weights of individual maize plants stover,
that is, above and below ground parts (shoot and root portions respectively)
were initially measured to obtain fresh weight values of their respective
shoot and root biomasses, after which the plant samples were also oven
dried at 50 °C for a period of 72 h and their dried weights were also
recorded.
Plant samples were milled, ground and passed through
a 0.5 mm sieve and then analyzed chemically. This was done to determine
nutrient recovery from amended soils and also nutrient accumulation within
plants tissue biomasses during the growing season up to harvest time.
Statistical Data Analyses
All data generated during the course of the experiment were analyzed
using the One Way Analysis of Variance (ANOVA) via the Graph InStat statistical
analytical package software. Significant means were detected using the
Dunnett`s Multiple Comparisons Test at 0.05 level of significance (p <
0.05) and 0.01 level of significance (p < 0.01).
RESULTS
Initial soil analyses for nutrients before addition
of amendments are shown in Table 1 for top and subsoil
samples respectively. pH values for top soil sample indicate a slightly
alkaline medium, while that for sub soil indicates a more acidic medium.
The high C/N ratios in both soil levels represent low contents of N in
the respective soil samples. Textural classification of the soil indicates
a sandy loam class for both levels of the soil being investigated.
The use of organic amendments significantly affected
soil chemical properties at both soil levels investigated. Statistical
analysis of the data obtained showed significant differences between nutrient
contents of amended soil and control soil (which had zero application
of amendments). In the topsoil samples, for the macronutrient elements
Ca, Mg, K, Na and P; 1 kg of Tithonia (T), 1 kg of water hyacinth
(WH) and T+WH (0.75:0.25 kg) treatments were highly significant for Mg
content compared to the control treatment (Table 2).
The effective cation exchange capacity (ECEC) in topsoil samples was not
significantly different in ECEC content value compared to control for
all the treatments (Table 2).
In the subsoil, treatment of sole application T (1 kg)
and WH (1 kg) were highly significant (p < 0.01) for nutrient elements
P and Na content in amended soil samples relative to control. Treatment
T+WH at its treatment ratios of 0.5:0.5, 0.25:0.75 and 0.75:0.25 kg recorded
significant values (p < 0.05) for P, K and Ca nutrient elements, respectively.
It was observed however that none of the treatments recorded significant
increase in Mg content with regard to the control treatment (Table
3). ECEC values for subsoil samples showed only sole WH treatment
(1 kg) as significant (p < 0.05) for ECEC content in its amended soil
compared to control treatment (Table 3).
| Table 1: |
Nutrient element analyses of pre amended experimental
soils |
 |
With regard to the micronutrient elements Mn, Fe, Zn
and Cu, sole treatment T (1 kg) was highly significant (p < 0.01) for
Fe, Cu and Zn content in the amended top soil samples compared to control
(Table 2). Treatment T+WH (0.25:0.75 kg) and WH sole
treatment (1 kg) had high significant effect on Mn and Fe as well as Fe
and Cu nutrient elements content in amended topsoil samples compared to
control soil.
In the subsoil samples, sole application of WH (1 kg)
had highly significant effects on Mn, Cu and Zn contents of soil with
regard to control. This was followed by treatment T+WH (0.25:0.75 kg)
that had highly significant values for Mn and Fe contents in amended soil
samples. Sole T treatment was significant (p < 0.05) for Mn and Zn contents
in amended soil respectively with regard to control (Table
3).
pH, %OC, %N and OM Content Analyses for Amended Soils
With regard to the pH values, percentage values for organic carbon
(OC) and nitrogen (N) for top and subsoil samples respectively, it was
observed that there was no significant difference in pH values for topsoil
compared to control for all treatments applied (Table 2).
A similar trend was observed in the amended subsoil samples, where there
was no significant difference for pH values between treated soils and
the control (Table 3). In the topsoil samples, all treatments
were highly significant (p < 0.01) for percentage N content in amended
soils in regard to control (Table 2); with the exception
of T+WH (0.5:0.5 kg). Conversely, only T in sole application (1 kg) was
observed to have significant percentage N value with all other treatments
recording values that were not significant compared to control in subsoil
samples (Table 3). Also, percentage OC values treatments
in the topsoil samples showed significant values for T+WH (0.25:0.75 kg)
and (0.75:0.25 kg) while all other treatments were not significant with
respect to control (Table 2). The percentage OC values
for subsoil samples (Table 3) showed that sole applications
of T and WH were highly significant (p < 0.01) for soil OC values compared
to control. Treatment T+WH (0.75:0.25 kg) was also significant (p <
0.05) for % OC content in amended soils compared to control. All other
treatments were not significant for OC content in their respective amended
soils.
Organic matter (OM) values for top soil samples had treatments
T+WH (0.75:0.25 kg) with highly significant values (p < 0.01) compared
to control. T+WH (0.25:0.75 kg) was also significant compared to control.
All other treatments were not significant (Table 2).
For sub soil samples, sole applications of T and WH were highly significant for
OM values; T+WH (0.25:0.75 kg) was also significant (p < 0.05) compared
to control (Table 3). All other treatments recorded
were not significant compared to control with regard to organic matter
content of soil samples.
| Table 2: |
Nutrient element analysis for amended and non amended
topsoil samples (post-harvest) |
 |
| *Significant at p < 0.05, **Highly significant at p < 0.01,
ns: Not significant, DMCT: Dunnett`s Multiple Comparison Test |
Plant Nutrient Element Recovery from Topsoil Samples
The trend of macronutrient uptake in the top soil samples showed that
maize biomass samples for all treatments recorded highly significant values
for uptake of elements with regard to control. Biomass samples for T+WH
(0.75:0.25 kg) were observed to have significant abundance (p < 0.05)
for macronutrient elements considered (that is, Ca, Mg, K, Na and P);
closely followed by T+WH (0.5:0.5 kg) which was also significant for Ca,
Mg, K and P uptake in its biomass samples with regard to control (Table
4).
| Table 3: |
Nutrient element analysis of amended and non amended
subsoil samples (post harvest) |
 |
| *Significant at p < 0.05, **Highly significant at p < 0.01,
ns: Not significant, DMCT: Dunnett`s Multiple Comparison Test |
For the micronutrients Fe, Cu, Zn and Mn, all treatments
showed a trend wherein plant biomass samples for T+WH (0.75:0.25 kg) were
significant (p < 0.01) for uptake of all micronutrient elements considered.
Biomass samples for T sole treatment (1 kg) was also highly significant
(p < 0.01) for Mn, Fe and Cu uptake from amended soil samples. WH sole
treatment (1 kg) and T+WH (0.25:0.75 kg) were significant (p < 0.05)
for Mn and Zn as well as Mn and Fe elements uptake, respectively in their
amended soil samples.
N uptake by maize biomass samples in topsoil samples
showed that T+WH (0.25:0.75 kg) and (0.75:0.25 kg) as well as WH (1 kg)
were highly significant (p < 0.01) for N uptake within its biomass samples
with regard to control (Table 4).
| Table 4: |
Nutrient element uptake values for maize test crop
in topsoil samples (post harvest) |
 |
| *Significant at p < 0.05, **Highly significant at p < 0.01,
ns: Not significant, DMCT: Dunnett`s Multiple Comparison Test |
| Table 5: |
Nutrient element uptake values for maize test crop
in subsoil samples (post harvest) |
 |
| *Significant at p < 0.05, **Highly significant at p < 0.01,
ns: Not significant, DMCT: Dunnett`s Multiple Comparison Test |
Plant Nutrient Element Recovery from Subsoil Samples
The trend of macronutrient uptake in the sub soil samples showed that
maize biomass samples for all treatments recorded highly significant (p
< 0.01) values for uptake of elements with regard to control. T+WH
(0.75:0.25 kg) was observed to show significant abundance of macronutrient
elements Ca, Mg, K and Na; closely followed by sole T and WH (1 kg) which
were also highly significant for Mg and K as well as K and Na elements
respectively with regard to control (Table 5).
Micronutrient elements uptake showed a trend where plant
biomass samples for sole T (1 kg) were highly significant (p < 0.01)
for uptake of micronutrient elements Mn, Fe and Zn in its amended soil
samples. Biomass samples of T+WH (0.5:0.5 kg) and T+WH (0.75:0.25 kg)
were significant for Zn and Cu as well as Fe and Zn elements uptake respectively
in their amended soil samples.
N uptake by maize biomass samples in subsoil samples
showed that T+WH (0.75:0.25 kg) was the only significant treatment (p < 0.01)
for N uptake within its biomass samples with regard to control (Table
5).
DISCUSSION
Soil samples amended by treatments of sole organic
amendment application (1 kg) and combined ratios of both amendments (0.5:0.5,
0.25:0.75 and 0.75:0.25 kg) generally showed significant difference for
all nutrient elements content in amended soil samples compared to control
treatment. It was observed however that combined treatment T+WH at its
various ratios and sole T and WH applications (1 kg) on the whole showed
no statistical significance for macronutrient elements content in the
amended topsoil samples except for Mg. This indicates that sole application
of organic amendments or in combination does not always contribute high
amounts of mineralized nutrients to amended soils when applied. This explains
the trend of no significant difference for effective cation exchange capacity
(ECEC) values in topsoil samples for all treatments. On the other hand,
sole treatments of T and WH (1 kg) showed high significant difference
for macronutrient element content in their amended subsoil samples. This
observed trend in the subsoil samples may be due to significant organic
matter addition to subsoil by organic amendments; which provided stable
soil aggregate conditions and prevented eroding/leaching of valuable nutrients
from subsoil samples. Thus application of organic amendments in eroded
sites may have more pronounced impact on soil chemical and physical properties.
Mbagwu and Piccolo (1989) reported that repeated application of organic
residues to soil improves physico-chemical properties of such soils. Studies
by Stark et al. (2006) showed that addition of green manures to
soil improved soil biology by increasing soil microbial biomass and activity.
Vinten et al. (2002) also reported increase in microbial activity
following application of organic amendments to soil, thus suggesting a
more responsive microbial community. The importance of beneficial microbes
in building a healthy soil microenvironment through enhancement of natural
soil processes cannot be overemphasized.
The micronutrient status of amended topsoil samples was
significantly improved by sole application of T, closely followed by T+WH
(0.25:0.75 kg) and WH sole treatment (1 kg) with regard to the control
treatment. Gachengo et al. (1999) reported relatively high concentrations
of other nutrients in Tithonia green biomass other than N, P and
K. The application of Tithonia biomass has been reported by Niang
et al. (1996) to have produced greater maize yield compared to
biomass of other common shrubs and trees in Western Kenya. Gunnarssen
and Petersen (2006) also highlighted that using composted water hyacinth
material could serve as quality manure for improving soil fertility conditions
and thus crop yields on the whole. These observed phenomena of significant
increase of macro and micronutrient elements contents in amended soils
with regard to control indicates the high fertilizing potentials of both
Tithonia green biomass and composted water hyacinth.
The pH values for both sub and topsoil samples were not
significantly affected by all treatments as regards control treatment
probably due to high buffering action of the organic amendments applied
as treatments in the soil samples. ECEC values in both amended top and
subsoil samples were not significant for all treatments compared to control,
which may indicate steady levels of exchangeable elements in investigated
soil samples which remained constant despite addition of organic amendments
to soil samples.
High occurrence of N and P increase quantity and activity
of soil microorganisms in soils (Marin, 2004), whose beneficial activities
in creating and sustaining a healthy soil environment cannot be overemphasized.
All treatments, except T+WH 0.5:0.5 kg showed high significant difference
in % N content with regard to control treatment in the topsoil samples.
This trend appears to be reversed however in the subsoil samples. Here
only Tithonia in sole application (1 kg) is observed to have significant
effect on % N content in its amended soil sample compared to control.
This observation indicates the high leaching prone feature of the experimental
soil being amended. Lal (1993) reported that soil erosion and compaction
as major management constraints for the Koalinitic Alfisols of the savanna
forest transition zones and sub humid savanna of tropical Africa. This
inadvertently implies that addition of significant amounts of organic
matter to these tropical soils can help reduce the trend of soil nutrient
depletion and leaching problems of soils found in the tropics. The organic
matter (OM) status of amended topsoil samples showed Tithonia and
water hyacinth [T+WH (0.75:0.25 kg) and (0.25:0.75 kg)] as significant
for OM content in their amended soils compared to control. This observation
buttresses the assertion that Tithonia can perform well as top
quality organic manure with good fertilizing value (Olabode et al.,
2007); while water hyacinth compost acting as soil conditioner improves
soil properties by building soil organic matter (Cooperband, 2002; Gunnarsson
and Petersen, 2006).
Sole applications of T and WH are the most significant
treatments (p < 0.01) for OM values for their amended subsoil samples
compared to control. The combination T+WH (0.25:0.75 kg) was also significant
for OM values in their subsoil samples. Studies by Spaccini et al.
(2002) showed that application of organic residues to soils could increase
soil organic matter (SOM), buffer soil, improve aggregate stability and
enhance water retention capacity of soils. This trend indicates the potential
ability and capacity of each of these organic resources to significantly
build organic matter in eroded soils when applied to such soils.
High significant macronutrient and micronutrient elements
uptake by maize plant biomass for T+WH in amended topsoil samples indicates
combination of organic amendments may be more useful for nutrient addition
to top and sub soils than sole applications of these amendments.
CONCLUSION
It is important to state that application of these
organic materials to nutrient depleted or poorly buffered tropical soils
goes beyond just increasing or replenishing nutrient element content of
soils so amended. Application of these organic residues to nutrient depleted
soils goes a long way in ensuring a sound nutrient management system within
the soil ecosystem over a sustained period by improving physical, chemical
and biological properties of such soils.
ACKNOWLEDGMENTS
The authors wish to acknowledge with thanks the
kind assistance of the Senate of the University of Ibadan for providing
the research grants and materials used in the study. We also appreciate
Mr. Basil Ohaegbulem of the Analytical Laboratory, International Institute
of Tropical Agriculture for his expert handling of the soil, compost and
manure analyses.
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