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ISSN No. 2454-6186 | DOI: 10.47772/IJRISS | Volume IX Issue X October 2025
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Integrated Effects of Lime and Fertilizer Applications on Soil
Properties and Sorghum Performance in Acidic Soils of Western
Kenya
Edwin K. Rotich
1
, Peter Oloo Kisinyo
2
, Peter Opala
3
1
Soil Science Department, University of Eldoret, Kenya
2
Department of Agronomy and Environmental Science
, Kenya
3
Department of Crops and Soil Sciences
, Maseno University, Kenya
DOI:
https://dx.doi.org/10.47772/IJRISS.2025.910000090
Received: 15 July 2025; Accepted: 25 July 2025; Published: 05 November 2025
ABSTRACT
Acidic soils cover significant portions of agricultural land in tropical regions, particularly in sub-Saharan Africa,
where soil acidity limits crop productivity through multiple mechanisms, including aluminum toxicity,
phosphorus fixation, and impaired nutrient cycling. In Western Kenya, where smallholder farmers
predominantly grow sorghum (Sorghum bicolor L.) as a staple crop, these soil constraints contribute to chronic
yield gaps. While agricultural lime and mineral fertilizers are recognized solutions for soil acidity amelioration,
their site-specific interactions and comprehensive effects on both soil health and crop performance remain
insufficiently documented. This study evaluated the effects of liming and nutrient microdosing on soil chemical
properties and sorghum (Sorghum bicolor (L.) Moench) productivity in the acidic soils of Western Kenya, using
factorial field trials conducted in Kakamega and Siaya counties. Treatments combined two lime levels (0 and 4
t ha⁻¹) with varying nitrogen (0, 18.8, 37.5, and 75 kg N ha⁻¹) and phosphorus (0, 6.5, 13, and 26 kg P ha⁻¹) rates.
Application of 4 t ha⁻¹ lime significantly (p ≤ 0.05) improved soil chemical properties, increasing soil pH by 20–
27%, reducing exchangeable aluminum by 56–89%, enhancing available phosphorus by up to 57%, and
increasing total nitrogen by 8–17%. Additionally, soil organic carbon was significantly elevated (p < 0.001),
with the greatest improvement (39%) observed in Siaya. Microdosing at 37.5 kg N and 13 kg P ha⁻¹ (N
37.5
P
13
)
produced the highest sorghum biomass and grain yield responses, with biomass yield increasing by 62–69% and
grain yield significantly enhanced at Kakamega (p < 0.001). Grain yield over the control rose by 73%, while
agronomic efficiency peaked at 24.1 kg grain kg⁻¹ nutrient at Siaya. Nutrient uptake also improved under liming
and optimal fertilization, with stover nitrogen uptake increasing by 55% at Kakamega and grain phosphorus
uptake rising by 44% at Siaya Site 2 (p < 0.05). These findings demonstrate that integrating site-specific liming
with nutrient microdosing can substantially improve soil fertility and sorghum productivity in acid-degraded
soils of Western Kenya.
Keywords: Soil acidity, Liming, Nutrient microdosing, Sorghum productivity, Western Kenya
INTRODUCTION
Nearly 4000 million hectares of the global land is composed of acid soils. This is almost 30 % the total ice-free
land and makes approximately 40 % of the arable land world over (Zheng, 2010). Historically, acid soils have
resisted agricultural use principally for the high level of toxic aluminum and their high phosphorus fixation
capacity. This P transformation process is pH-regulated, organic matter content and soil biological properties
(Asomaning, 2020; Prasad & Chakraborty, 2019). The addition of chemical P fertilizers leads to an initial spike
in P availability(Sato & Comerford, 2005), followed by P adsorption and precipitation, which will result in a
substantial decrease in P availability over time (Muindi et al., 2015).
Liming is an ancient agronomic practice of correction of soil acidity, especially under tropical conditions in
which acidic soils constrain agricultural yields.
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Lime application neutralizes acidity in the soil through reaction with hydrogen (H⁺) and aluminum (Al³⁺) ions
and, thereby, raises the pH of soil and lowers aluminum toxicity (Mullen et al., 2016). This chemical reaction
increases the availability of these necessary nutrients, mainly nitrogen and phosphorus, that tend to be deficient
in acidic soils because they are fixed by aluminum and iron compound materials (Gatiboni & Hardy, 2023).
Soil pH increase as a result of liming also enhances a more optimal soil microbial community environment. Soil
microorganisms like nitrifying bacteria are activated at higher pH, leading to increased nitrogen cycling and
availability (Mitsuta et al., 2025). Specifically, the nitrogen concentration of plants is promoted by the process
of ammonium to nitrate conversion, which is readily absorbed by plants (Mitsuta et al., 2025).
In sorghum development, efficient use of nitrogen during early stages of growth is required in order to promote
yield and vigor. Any enhancement in nitrogen availability through liming can therefore play a critical role in
sorghum development, especially during the
Plants cannot absorb soil P at low pH because pH conditions form insoluble iron (Fe) and aluminum oxides
complexes. The alkaline nature of lime reduces the solubility of Fe and Al compounds when the pH reaches
neutral levels thus enabling the release of plant-available P (Wagner, 2024). The early development of sorghum
roots depends heavily on adequate P accessibility during its initial growth stages. The agricultural benefits
derived from lime treatment in soils require further evaluation of possible adverse consequences. High levels of
lime treatment coupled with pH values higher than 6.5 results in the formation of additional chemical factors
that can obstruct plant growth. Soil pH increases create a situation where the solubility of micronutrients zinc
(Zn), manganese (Mn), iron (Fe), and copper (Cu) decreases making them less available to plants (Fageria et al.,
2002; Gondal et al., 2021; Rengel, 2003; Riaz et al., 2020). Sufficient micronutrients are essential for sorghum
reproductive development and enzyme activities and photosynthesis regardless of any limiting factors. Excessive
lime concentrations in the environment result in nutrient deficiencies which produces interveinal chlorosis while
damaging grain formation.
Soil phosphorus availability depends intensively on pH and the concentration of calcium ions (Ca²⁺) in the soil.
Acidic soil conditions (pH lower than 5.0) allow phosphate ions to combine with iron (Fe) and aluminum (Al)
to form insoluble compounds that plants cannot access. In alkaline solutions with more than 6.0 pH phosphate
ions bind with calcium to produce insoluble tricalcium phosphate and other poorly absorbable calcium phosphate
compounds (Mkhonza et al., 2020). Soil pH should be kept at about 6.0 to provide plants with the best available
phosphorus levels.
Liming soil with high pH and calcium content leads to insoluble calcium phosphate compounds which form in
phosphate-treated soils. liming therefore, leads to a reduction in phosphorus fertilizer effectiveness and creates
an impact on the available amount of phosphorus for plants.
Lime applications to soil enhance pH levels which results in elevated nitrate (NO₃⁻) concentrations in the soil.
The liming process combined with calcium application creates insoluble precipitates of calcium phosphate that
become abundant. Such treatment renders soil P inaccessible to plants thus leading to reduction in their efficiency
levels (Mkhonza et al., 2020).
In crops like sorghum, which are sensitive to nutrient stress, such nitrogen losses through leaching can lead to
poor performance and decreased yields. Therefore, careful management of nitrogen fertilization and liming is
essential to minimize leaching losses and optimize nitrogen use efficiency.
The successful application of nitrogen fertilizers and liming programs will protect soil from harmful leaching
effects and make nitrogen more accessible to farmers. Research shows that the effects of liming in sorghum
production systems rely on both the amount of applied lime plus the time of season application. Soil nutrient
equilibrium becomes permanently damaged as farmers choose to over-lime their land or introduce lime before
the appropriate time. The application of excessive lime or premature distribution causes yield reductions in crops.
Farmers in Brazil achieved improved sorghum yields through liming their fields in combination with proper
phosphorus applications (Silveira et al., 2018). The research highlighted how achieving best outcomes requires
balancing the applications of lime together with fertilizer.
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The outcome of applying specific lime rates to soil will vary according to initial nutrient content alongside soil
texture and organic matter levels. Soil analysis results should determine specific treatments with lime which
avoids damaging chemical balances in the soil (Omollo et al., 2016). Research in Kenya demonstrates that crop
productivity is directly influenced by how lime is distributed either by broadcasting or banding alongside rates
of application. The research demonstrates that localized approaches to lime management will help achieve
maximum agricultural output.
MATERIALS AND METHODS
Study Sites
The study was conducted across three sites with contrasting edaphic properties in Western Kenya. The
Kakamega site (KK) featured Ferralsols with an initial pH of 3.38 ± 0.10 and available phosphorus of 3.26 ±
0.35 mg kg⁻¹. Sega 1 (SY1) and Sega 2 (SY2) both had Acrisols, with SY1 showing higher initial acidity (pH
3.51 ± 0.11) compared to SY2 (pH 3.40 ± 0.09). Baseline available phosphorus was 2.98 ± 0.36 mg kg⁻¹ at SY1
and 2.59 ± 0.46 mg kg⁻¹ at SY2.
Fig. 1: Map showing Siaya experimental site
Fig. 2: Map showing Kakamega experimental site
Experimental Design
A factorial experiment combining two lime levels (0 and 4 t ha⁻¹) with three NP fertilizer doses (N₀P₀, N₃₇.₅P₁₃,
and N₇₅P₂₆) was implemented in a randomized complete block design with three replications at each site. The
lime treatment used finely ground agricultural limestone (85% calcium carbonate equivalent), while fertilizer
treatments applied urea and triple superphosphate as N and P sources, respectively.
Data Collection and Analysis
Soil samples were collected at 0-20 cm depth before planting and after harvest for analysis of pH (1:2.5 soil:
water), available phosphorus (Bray-1 method), exchangeable aluminum (1M KCl extraction), total carbon and
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nitrogen (dry combustion). Sorghum grain yield was determined at physiological maturity from net plot harvests,
while biomass yield included total above-ground plant material. Statistical analysis employed two-way ANOVA
to assess main and interaction effects, with mean separation using Tukey's HSD test at p < 0.05. Regression
analyses examined relationships between fertilizer doses and response variables. Model adequacy was evaluated
through R² values and residual analysis.
RESULTS
Soil pH
Soil pH was likewise observed to rise steadily and significantly following the application of lime, and all sites
showing some modification. Unamended soils (0tha x N
0
P
0
) ranged in pH from 4.63 to 5.19, which provided a
definition of strong to moderate acidity. Alkalinization followed subsequently after the application of 4 t ha⁻¹ of
lime. The largest fluctuation was seen in the 4tha x N
75
P
26
treatment where soil pH increased to a level of 6.23,
which shows a general increase of 0.8 to 1.6 units of pH from control. These increases were up to 34% rise in
the soil pH over the initial level. Low doses of fertilizer, i.e., 4tha x N
37.5
P
13
, raised high levels of pH by 0.9–1.4
units, testifying to the synergistic action of lime with some fertilization. Statistical significance of the lime effect
was very significant (p < 0.001) at all the locations, but the effect of the fertilizer dose alone was moderate at
one location only (p = 0.024).
Available phosphorus
Available phosphorus (P) was very responsive to application of lime and fertilizer rate (Table 1). Control plots
were characterized by low P concentration levels ranging from 2.01 to 2.92 mg kg⁻¹, which conformed to P
fixation in acidic soils. The addition of lime, particularly under more nutrient-deficient regimes, elevated the
availability of P significantly. The 4tha x N
75
P
26
treatment yielded the largest P values, 7.52 to 8.16 mg kg⁻¹,
increases of over 160–300% above control. Mid-level treatments 4tha x N
37.5
P
13
and 4tha x N
18.8
P
6.5
also
achieved sizable gains, typically double P values above baseline. Lime (p < 0.001) and fertilizer (p < 0.001) were
significant statistically, with the recommendation that integrated management was advisable for use in
recovering phosphorus in acid-affected soils.
Exchangeable Aluminum
Exchangeable aluminum (Al), being one of the primary indicators of acid toxicity, fell significantly with the
addition of lime (Table 1). Control plots yielded 1.59–2.00 Cmol kg⁻¹ values, which are low for root growth and
nutrient acquisition. The 4tha x N75P26 treatment brought Al values down to 0.87 Cmol kg⁻¹ or decreases of
44–57% relative to control.
Reductions were strongest in blends of lime with moderate to high application rates of nutrients, i.e., 4tha x
N
37.5
P
13
and 4tha x N
18.8
P
6.5
, where contents of Al reduced consistently below 1.25 Cmol kg⁻¹. Lime had
significant effects on Al at all sites (p < 0.001), and an interaction effect between fertilizer and lime was
significant (p < 0.05) in the most acid-sensitive soils, which suggests that amelioration as measured by aluminum
is greater when the two amendments are applied together.
Table 1: Effects of Lime and Nutrient Microdosing on Soil pH, Available Phosphorus (P), and Exchangeable
Aluminum (Al) Across Three Study Sites (Kakamega, Sega 1, and Sega 2)
-----------Soil pH --------
----- Soil P (mg kg
-1
) ----
----- Soil Al (Cmol kg
-1
) -----
Treatment
KK
SY1
SY2
KK
SY1
SY2
KK
SY1
SY2
0tha x N
0
P
0
5.19
abc
4.63
a
5.14
a
2.68
a
2.92
a
2.01
a
2.23
c
1.86
b
1.59
b
0thaxN18.8P6.5
5.11
ab
4.67
a
5.16
a
3.75
ab
3.09
a
2.76
ab
2b
c
1.83
b
1.6
b
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0tha x N
37.5
P
13
5.4
abcd
4.72
a
5.29
ab
4.07
ab
3.48
ab
3.26
abc
1.62
abc
1.79
b
1.56
b
0thaxN
75
P
26
5.07
a
4.68
a
5.42
ab
4.27
abc
3.87
ab
4.15
abcd
1.61
abc
1.73
b
1.5
b
4tha x N
0
P
0
5.87
cd
5.46
b
5.8
bc
4.25
ab
3.22
a
4.82b
cd
1.13
ab
1.09
a
1.43
b
4tha x N
18.8
P
6.5
5.76
abcd
5.65
b
5.83
bc
4.73
bc
3.9
ab
5.57
cde
1.25
ab
0.92
a
1.17
a
4tha x N
37.5
P
13
5.77b
cd
5.32
b
6.04
c
6.16
cd
4.93
ab
6.25
de
1.11
ab
0.88
a
1.11
a
4tha x N
75
P
26
6.04
d
5.48
b
6.23
c
7.52
d
5.42
b
8.16
e
0.89
a
0.87
a
1.12
a
SED
0.22
0.14
0.18
0.61
0.65
0.83
0.29
0.19
0.06
CV%
8.49
5.67
6.8
27.47
35.63
38.03
41.71
29.82
9.13
P-value (Lime)
<0.001
<0.001
<0.001
<0.001
<0.05
<0.001
<0.001
<0.001
<0.001
P-value (Fert)
NS
NS
0.0238
<0.001
<0.05
<0.001
NS
NS
<0.001
P-value (Lime x Fert)
NS
NS
NS
NS
NS
NS
NS
NS
<0.05
Oil Nitrogen
Table 2 shows that soil nitrogen was significantly increased after fertilizer and lime application with equal trends
at all trial sites. The sum of total nitrogen varied from 0.03% to 0.16% in control (0tha x N
0
P
0
), indicating low
fertility of acid-stressed plots.Application of fertilizer alone raised nitrogen content moderately. However, 4 t
ha⁻¹ lime and nutrient microdosing provided the most significant improvement. Both 4tha x N
75
P
26
and 4tha x
N
37.5
P
13
treatments had 0.25% N, an absolute increase of as much as 0.22% or relative increases of as much as
733% compared to initial values in the driest location. Statistical analysis confirmed that both lime and fertilizer
both significantly (p < 0.001) affected nitrogen at all locations. Lime and fertilizer rate improved added N
availability and retention, and fertilizer rate improved N with
Table 2: Effects of Lime and Nutrient Microdosing on Total Soil Nitrogen (N), Soil Organic Carbon (SOC), and
Carbon-to-Nitrogen Ratio (C:N) Across Three Sites (Kakamega, Sega 1, and Sega 2)
--------Soil N (%) -------
--------Soil OC (%) ------
-------Soil CNR------
Treatment
KK
SY1
SY2
KK
SY1
SY2
KK
SY1
SY2
0tha X N
0
P
0
0.16
a
0.03
a
0.08
a
1.98
a
1.37
a
1.26
a
12.69
b
64.53
b
15.8
a
0tha X N
18.8
P
6.5
0.19
ab
0.09
bc
0.08
ab
2.16
abc
1.48
ab
1.34
ab
11.53
ab
16.1
a
14.13
a
0tha x N
37.5
P
13
0.2
b
0.13
c
0.09
ab
2.26
bcd
1.6
bcd
1.44
abc
11.27
ab
13.16
a
14.3
a
0tha X N
75
P
26
0.21
bc
0.14
cd
0.1
abc
2.33
cde
1.73
cde
1.54
bcd
11.23
ab
12.42
a
13.92
ab
4tha x N
0
P
0
0.19
ab
0.04
ab
0.09
ab
2.09
ab
1.54
abc
1.57
bcd
11.82
ab
58.36
b
16.19
a
4tha x N
18.8
P
6.5
0.23
cd
0.13c
0.1bc
2.37
cde
1.69
bcd
1.7
cde
10.14
abc
13.94
a
14.63
a
4tha x N
37.5
P
13
0.25
d
0.15
cd
0.12
cd
2.47
de
1.81
de
1.78
de
10.01a
13.14
a
13.42
a
4tha x N
75
P
26
0.25
d
0.2d
0.13
d
2.54
e
1.95
e
1.92
e
10.13
ab
10.82
a
12.12
a
SED
0.01
0.02
0.01
0.07
0.07
0.09
0.85
8.41
1.46
CV%
9.94
35.1
15.14
6.43
9.08
11.75
16.27
70.52
21.58
P-value (Lime)
***
***
***
***
***
***
**
NS
NS
P-value (Fert)
***
***
***
***
***
***
**
***
**
P-value (Lime X Fert)
NS
NS
NS
NS
NS
NS
NS
NS
NS
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a normal dose-response relationship. The findings confirm the need for the use of lime in conjunction with a
particular input of nutrient to rebuild the level of soil nitrogen under acid-degraded conditions.
Soil Organic Carbon
Treatment effects on SOC content also rose in a parallel manner as shown in Table 2. Control plots recorded
moderate carbon stocks of between 1.26% and 1.98% SOC. SOC was somewhat improved with fertilizer alone
treatment but was optimized when lime was added. SOC contents between 1.92% and 2.54% were recorded in
4tha x N
75
P
26
treatment, representing a 51% increase from the control. Comparable 0.3–0.5 percentage point or
20–40% gains were achieved by mid-treatment applications like 4tha x N
37.5
P
13
and 4tha x N
18.8
P
6.5
, indicating
that moderate fertilizer application with addition of lime can consistently enhance organic matter. Both lime and
fertilizer significantly increased SOC at all sites (p < 0.001). Lack of interaction between fertilizer and lime
suggests additive rather than synergistic action. The results support the suggestion that enhanced root biomass,
microbial activity, and residue incorporation due to relieved acidity limitation could be accountable for carbon
sequestration under fertilizer and lime treatment.
Soil C:N Ratio
Table 2 shows that Carbon-to-Nitrogen (C:N) ratio decreased largely at Siaya Site 1 and Kakamega. With a mean
of 12.7 in Kakamega, close to well-composted organic waste, and up to 64.5 at Siaya Site 1, C:N in control
treatments (0tha x N
0
P
0
) ranged widely. The C:N ratio was reduced quite noticeably by fertilizer alone, especially
at medium to high levels (e.g., N
37.5
P
13
and N
75
P
26
), indicating higher availability of nitrogen than carbon content.
For instance, at Siaya Site 1, C:N was reduced over 75% for the 4tha x N
37.5
P
13
and 4tha x N
18.8
P
6.5
treatments,
from 64.5 in the control to approximately 13.2–13.9. This also verifies the restorative action of simultaneous
nutrient supplementation to the organic matter balance. Concurrently, the C:N ratio declined to approximately
10.0–10.1 in the case of 4tha x N
37.5
P
13
and 4tha x N
75
P
26
treatments at Kakamega by up to 21% less than control.
This implies that applications of fertilization and liming led to enhanced microbial digestion and nitrogen
mineralization.
Performance of Sorghum Grain and Biomass Yield
Sorghum grain yield (Fig.3) likewise shared comparable patterns of treatment sensitivity, albeit with relatively
smaller treatment ranges than biomass. Control levels at 0.5 and 0.81 t ha⁻¹ were used as the points of reference
from which the treatments were derived. Treatment 4tha x N
75
P
26
demonstrated highest improvement in SGY
with a maximum of 3.0 t ha⁻¹ and showing 270–350% yield improvement above control. Of particular interest,
150–250% advances were generated by treatments qualifying as moderate inputs, like 4tha x N
18.8
P
6.5
and 4tha
x N
37.5
P
13
, with mean values for SGY of 1.4 to 2.5 t ha⁻¹ across sites. Throughout all the treatments, increase in
gain yield was most significantly associated with the application of lime because unlimed plots always produced
less than limed plots at any fertilizer level. These results demonstrate the potential of lime to enhance nutrient
uptake and subsoil limitations, and induce measurable increases in sorghum grain yields with integrated
management practice.
Biomass yield of sorghum showed a consistent upward response to lime application combined with increasing
levels of fertilizer microdosing (Fig.3). Across sites, the control treatment (0tha x N
0
P
0
) resulted in the lowest
SBY values, ranging from approximately 2.0 to 4.3 t ha⁻¹, depending on baseline soil conditions. On the other
hand, maximum biomass was seen with 4tha x N
75
P
26
with SBY to the value of 14.4 t ha⁻¹ in conditions of
optimal growth — an increase by over 250–400% over control. Intermediate rates using half of the nutrient rates
like 4tha x N
37.5
P
13
and 4tha x N
18.8
P
6.5
also showed impressive improvement with biomass yields considerably
more than 10 t ha⁻¹, which is equivalent to a 130–250% increase above non-fertilized treatments. The results
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show that application of lime is a major yield booster, especially when combined with medium rates of nitrogen
and phosphorus application. The low nutrient rates alone were inconsistent in performance, but improved
drastically when applied in combination with lime, hence confirming the synergistic action of acidity increase
towards optimizing biomass production.
Fig. 3: Effect of Lime and Nutrient Microdosing on Sorghum Biomass and Grain Yield Across Kakamega, Sega
1, and Sega 2 Sites
Correlation Between Soil Chemical Properties and Sorghum Yield Components
Pearson correlation analysis was conducted to explore the relationships between soil chemical properties and
sorghum grain yield (SGY) and biomass yield (SBY) across the three study sites (Kakamega, Sega 1, and Sega
2). The analysis revealed several significant relationships that underscore the pivotal role of soil amelioration in
enhancing crop productivity in acidic soils.
Soil pH showed a strong positive correlation with SGY (r = 0.76, p < .001) and SBY (r = 0.71, p < .001),
suggesting that liming substantially improved sorghum performance by reducing soil acidity. Conversely,
exchangeable aluminum exhibited a strong negative correlation with SGY (r = -0.72, p < .001) and SBY (r = -
0.70, p < .001), indicating that higher Al toxicity adversely affected yield outcomes.
Available phosphorus was positively associated with both SGY (r = 0.66, p < .001) and SBY (r = 0.68, p < .001),
demonstrating the importance of P availability, likely enhanced by pH correction and targeted fertilization.
Similarly, total soil nitrogen showed moderate to strong positive correlations with SGY (r = 0.61, p < .01) and
SBY (r = 0.63, p < .01), while soil organic carbon was also positively related to both yield parameters (r = 0.59
and 0.60 for SGY and SBY, respectively, p < .01).
DISCUSSION
Soil pH
Progressively increasing soil pH with the treatments is due to the neutralizing effect of farm lime, primarily
calcium carbonate (CaCO₃). While reacting with hydrogen ions (H⁺) from acidic components of the soil upon
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contact, lime decreased proton activity in soil solution and thereby increased the pH:
CaCO
3
+2H→Ca
2+
+H
2
O+CO
2
↑
In addition to the reduction in soil acidity, this reaction allowed for exchange of exchangeable Al³⁺ and H⁺ on
colloidal surfaces, with an overall increase in base saturation of the soil. The observed maximum increase in pH,
6.23 in treatment 4tha x N
75
P
26
, was an indication of additive influence of lime buffering and possible rhizosphere
crop of pH due to root activity following fertilization.
Similar pH increase in weathered soils across tropical regions was monitored by Kisinyo et al. (2015) and
Anderson et al. (2013) after applying lime to soils and synergistic pH increase in acid soils across Kenya was
monitored by Muindi et al. (2015) after they added moderate amounts of phosphorus to Kenyan acid soils and
lime. Acidification under fertilizer-alone treatment, especially where ammonium-sourced nitrogen was used, is
also in line with reported nitrification processes:
NH
4
+
+2O
2
→NO
3
−+2H
+
+H
2
O
This produces more H⁺ ions, which again decrease pH unless regulated by liming.
Available Phosphorus
In highly acidic soils, phosphate ions (PO₄³⁻) can be susceptible to fixation by Al³⁺ and Fe³⁺ through precipitation
reactions:
Al
3+
+H
2
PO
4
−→AlPO
4
↓+2H
+
These reactions constrain phosphorus availability. By raising soil pH and diminishing Al³⁺ activity, lime
interferes with such fixation processes and increases P solubility. This is evidenced by the elevation in accessible
P values of 2.01-2.92 mg kg
-1
in control plots to 7.52-8.16 mg kg
-1
in 4tha x N
75
P
26
.
Patterns of simultaneous P recovery were similarly mentioned by Haynes (1982) and Sanchez & Uehara (1980),
and recently by Opala (2023) especially when liming had reduced, but before Al saturation, before phosphorus
addition. Increased pH could have also triggered microbial P mineralization and desorption by roots from
colloidal surfaces into solution, enhancing mid-level nutrient treatments availability.
Though lime minimized P fixation, fertilizer application provided labile P, which — under conditions of lowered
Al toxicity — was held in solution within the soil and was more easily absorbed. Literature warns that overliming
will ultimately result in precipitation of calcium phosphate if pH levels are greater than optimal levels (>6.5),
although all levels taken during this trial were below this figure.
Exchangeable Aluminum
Exchangeable aluminum (Al³⁺), which is characteristic of acid soils with pH <5.5, decreased substantially after
lime treatment. Al³⁺ increases in solubility in acid soils and can drastically suppress root elongation and nutrient
uptake. The increase in exchangeable Al — as much as 57% in limed plots — indicated hydrolysis and
precipitation of Al³⁺ in the form of insoluble aluminum hydroxide:
Al
3+
+3OH
−
→Al(OH)
3
↓
Such a process is favored by soils with high pH and basic to neutral conditions. Haynes (1982) labeled such a
path as a critical process for alleviating aluminum toxicity following liming, a process evidenced in African acid
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soils where lime caused substantial reduction of active fractions of Al in a matter of years (Muindi et al., 2015;
Wilding & Drees, 1985).
The absence of a large lime × fertilizer interaction on Al indicated that the liming effect-controlled aluminum
detoxification and could be partly independent of fertilizer application in the short term.
Soil Organic Carbon (SOC)
Addition of fertilizer and lime favorably enhanced soil organic carbon (SOC), and the latter showed a progressive
increase with the intensity of treatments. The initial values of SOC from the control plots ranging from 1.26%
to 1.98% agreed with the moderate organic matter accumulation in tropical upland soils. Lime exhibited the
greatest SOC gain, while sole fertilizer treatment had the lowest. The 4tha x N
75
P
26
yielded 1.92% to 2.54% SOC
levels equivalent to absolute gains of 0.56 percentage points, or a 51% improvement over control. Lime and
microdose treatments, like 4tha x N
37.5
P
13
and 4tha x N
18.8
P
6.5
, generated 20–40% gains consistent with the
function of moderate fertilizer microdosing under the relief of pH constraints simultaneously.
Greater production of root biomass and associated microbial activity by removal of the acidity constraint would
in turn facilitate such an enhancement. Acid soils result in organic matter accumulation due to sluggishness in
microbial degradation and decomposition. Microbial enzymes, namely cellulases and proteases that function
optimally at neutral pH have been found to be suppressed by the addition of lime (Sumner & Noble, 2003). Also,
increased availability of nutrients favors plant growth, which favors return of residues and rhizodeposition,
further increasing the reserve of organic carbon. Incidentally, additive effect is supported by statistical
independence of lime and fertilizer effects since none of the interactions were significant.
This is consistent with research findings of Chimdi et al. (2012), which indicate that SOC increased in Ethiopian
acid soils resulted independently from liming and fertilizer addition with additive effects from different
physiological as well as chemical pathways.
C:N Ratio
There were treatment-specific decreases in the carbon-to-nitrogen (C:N) ratio, notably in Siaya Site 1 and
Kakamega. Rats in control conditions varied immensely; in Kakamega, they were 12.7, analogous to stabilized
compost values (Stevenson, 1994); in Siaya Site 1, 64.5, with nitrogen-deficient organic matter that would tend
to immobilize by microorganisms.
C:N ratios were greatly lowered by fertilizer treatment per se, especially at the moderate to high regimes. Co-
application of lime-fertilizer enhanced the trend. For instance, 4tha x N
37.5
P
13
and 4tha x N
18.8
P
6.5
lowered the
C:N ratio at Siaya Site 1 to approximately 13.2-13.9, i.e., over 75% lower compared to the control. Similarly,
under these treatments, Kakamega dropped to 10.0–10.1, i.e., enhanced nitrogen mineralization.
These results imply several interconnected mechanisms: lime treatment promoted microbial breakdown of
organic refuse, mobilizing additional nitrogen through ammonification; supplemental N augmented inorganic N
availability, complementing the C:N deficiency. Furthermore, alleviating root stress and promoting greater
rhizodeposition of labile carbon substrates, alleviated aluminum toxicity may have indirectly contributed to
increased microbial activity.
In Andosols of volcanism, Inoue et al. (2001) likewise showed similar declines in C:N under limed fertilizer
treatment. Combined amendments enhanced stoichiometry of the soil through compulsion of decomposition
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equilibrium to net mineralization. Directionality of fertilizer and lime effect on C:N signals complementarity in
function, although no interaction effect was statistically significant.
Scientific Implications
These results collectively highlight the critical role of lime in managing acid soils. Beyond raising pH, lime
reduces toxic aluminum levels and unlocks phosphorus that might otherwise remain unavailable. Fertilizers,
while essential for supplying nutrients, can further acidify soils if applied without liming, potentially
exacerbating constraints on root growth and nutrient uptake. Moreover, the subtle but positive influence of lime
on organic matter dynamics (C:N ratio and SOC) suggests additional long-term benefits for soil biological
functioning and fertility.
Integrated soil fertility management—specifically combining lime with balanced fertilization—is clearly more
effective than using either input in isolation. Such strategies are especially vital for smallholder systems in acid
soil regions, where restoring soil health is foundational to achieving reliable crop productivity.
The results of this study reinforce the critical role of integrated soil fertility management (ISFM) in improving
sorghum productivity in acidic tropical soils. The observed improvements in soil chemical properties—
particularly increased pH, reduced exchangeable Al, and enhanced phosphorus availability—translate directly
into increased sorghum grain and biomass yields. These outcomes are consistent with earlier findings in acid
soil contexts, where lime application has been shown to correct soil acidity, alleviate aluminum toxicity, and
improve nutrient use efficiency (Nziguheba et al., 2022; Vanlauwe et al., 2015).
Physiological and soil chemical drivers of sorghum yield response
Under combined applications of lime and fertilizer, sorghum grain and biomass yields were significantly
increased, reflecting a mix of chemical amelioration of the soil and physiological stimulation. The underlying
modification of the chemical root zone environment accounted for the evenly distributed increase in yields across
treatment levels for the 2016–2018 seasons. In acidic soils, exchangeable acidity and aluminum saturation are
known to significantly limit root growth and nutrient uptake. Lime application, especially at 4 t ha⁻¹, was crucial
in neutralizing these conditions (Fageria & Baligar, 2008). In addition to detoxifying Al³⁺ via hydroxide
precipitation, the pH rise also altered the sorption equilibria that control phosphorus dynamics. Phosphate ions
are held in acid soils by complexation with Al and Fe oxides. Liming would most likely have released plant-
available phosphorus by increasing the pH and inhibiting the formation of insoluble aluminum phosphate
complexes.
Considering improved sorghum grain yield (up to 3.0 t ha⁻¹ under 4tha
-1
xN
75
P
26
) and biomass yields (up to 14.4
t ha⁻¹), the subsequent chemical changes created an improved permissive nutrient acquisition environment.
Central metabolic processes were physiologically boosted by the increased availability of nutrition. Nitrogen
availability facilitated the development of proteins and chlorophyll, which was vital to grain development and
photosynthetic function. Phosphorus uptake simultaneously stimulated root architecture development and ATP
synthesis, enhancing the plant’s capacity to absorb water and other nutrients. Reproductive success and enhanced
vegetative growth were the increased outcomes. Also, by increasing pH to levels most conducive to enzymatic
activity, liming could have initiated population growth among rhizosphere microbes. Liming, as per Enesi et al.
(2023), enhanced mineralization and bioavailable nutrient release by stimulating bacterial populations involved
in organic matter turnover that are suppressed at pH values less than 5. Even at reduced application levels, this
action most likely enhanced the efficiency of microdosed fertilizer applications. In spite of the use of fertilizer,
continued poor productivity on the unlimed plots ensured that acid subsoil conditions remained a limiting factor
until they were corrected. Even with external inputs, nutrient uptake becomes inefficient in such conditions
because roots are restricted both geographically and functionally (Sanchez, 1976). Thus, the application of lime
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served as a structural facilitator of physiological processes as well as a chemical modification. These results were
similar to those published by Getahun et al. (2019) and Soileau & Bradford (1985) on sorghum in similarly
acidic tropical soils, where liming significantly increased dry matter buildup and grain filling capacity. The
present study's responsiveness to moderate fertilizer doses under limed conditions, however, suggested a
threshold-based yield dynamic, beyond which diminishing returns might occur. This phenomenon needs more
investigation in relation to the nutrient use efficiency of sorghum under various edaphic constraints.
Correlation Analysis
Sorghum yields and chemical soil factors were positively correlated by Pearson correlation analysis at the
Kakamega, Sega 1, and Sega 2 locations. Grain yield (SGY; r = 0.76, p < 0.001) and biomass yield (SBY; r =
0.71, p < 0.001) were directly correlated with soil pH, affirming the vital role that correction of acidity plays in
boosting yields. The increase in pH following lime addition likely stimulated root and microbial growth and
reduced aluminum saturation and enhanced nutrient solubility. The positive correlation showed that the greater
volume of rooting and increased chemical conditions generated by correction of pH were advantageous to
sorghum.
On the other hand, exchangeable aluminum (Al³⁺) negatively correlated with SGY (r = –0.72, p < 0.001) and
SBY (r = –0.70, p < 0.001), indicating that aluminum toxicity remained the prime constraint under the acid
conditions which had not been altered. Al³⁺ has been known to inhibit symbiotic microbial processes, nutrient
uptake, and root growth, and hence this finding was expected. The reverse correlation validated previous findings
that lime amendment enhanced sorghum yields and root-zone parameters by precipitating and hydrolyzing Al³⁺
as Al(OH)₃.
Both SGY (r = 0.66, p < 0.001) and SBY (r = 0.68, p < 0.001) were significant positive correlations with available
phosphorus (P), and this might be due to more P desorption and less fixation at high pH values. Formation of
insoluble aluminum phosphates constrains phosphorus solubility under acid soils; the pH-related correlation
established herein validated that phosphate ion release controlled by pH directly influenced sorghum nutrient
and dry matter uptake.
Grain yield (r = 0.61, p < 0.01) and biomass yield (r = 0.63, p < 0.01) were significantly positively correlated
with the total soil nitrogen, and thus nitrogen supply was again an important factor determining yield. Nitrogen
supply could have increased due to the fact that pH recovery stimulated nitrification and mineralization
processes. Equally, SOC was significantly correlated with SGY (r = 0.59) and SBY (r = 0.60), the latter two also
significant at p < 0.01, indicating its role in enhancing soil structure, microbial activity, and the ability of cation
exchange for nutrients.
All these interconnections established that sophisticated chemical and physiological feedbacks triggered by soil
amendments were responsible for the increments in sorghum production. In acidic tropical systems, the interplay
among pH, aluminum, phosphorus, nitrogen, and carbon reiterated that global soil fertility restoration was
indispensable in order to acquire the optimum agronomic results.
CONCLUSIONS
The research proved that the integration of 4 t ha⁻¹ application of agricultural lime with moderate to high
microdosed applications of fertilizers markedly enhanced sorghum yield and chemical soil properties in acidic
western Kenyan soils. N
37.5
P
13
and N
75
P
26
lime treatments consistently increased soil pH by as much as 1.6 units,
lowered exchangeable aluminum by as much as 57%, and increased available phosphorus by more than 300%
compared to controls. The application of chemicals gave grain yield of 3.0 t ha⁻¹ and biomass yield of as much
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as 14.4 t ha⁻¹, which equal relative increases of 270–400% at the locations in question.
Correlation analysis also revealed strong positive associations between sorghum yield and soil pH, available
phosphorus, total nitrogen, and organic carbon, and negative association of exchangeable aluminum with grain
and biomass yields. Of treatment combinations, lime at 4 t ha⁻¹ with intermediate nutrient rates (e.g., N
37.5
P
13
)
had persistent agronomic and chemical impacts under different soil conditions.
But where high application rates of fertilizers like N
75
P
26
are applied, careful adoption is indicated where buffer
potential and initial baseline fertility are low. High fertilizer uses entails risks like nutrient imbalance, inadvertent
acidification, or economic inefficiency in resource-constrained systems. Just as lime was required to counteract
acidity, excessive lime application in low-buffer potential soils might entail raising pH beyond optimal ceilings,
reducing solubility of phosphorus or upsetting microbial balance. Therefore, on-site calibration of fertilizer and
lime applications remains critical for sustainable soil fertility recovery as well as for maximization of crop
performance.
These results support the chemical and biological significance of targeted amendments in tropical acid and acid-
degraded soil rehabilitation and represent an integrated strategy towards improving the productivity of sorghum
based on equilibrated input utilization.
ACKNOWLEDGMENT
This research was supported by the McKnight Foundation, whose contribution is gratefully acknowledged. The
University of Eldoret provided essential infrastructure and expertise during the chemical analysis phase, and I
sincerely appreciate their invaluable support.
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