Soil Acidification and Lime Quality: Sources of Soil Acidity, Effects on Plant Nutrients, Efficiency of Lime and Liming Requirements

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Research and Reviews: Journal of Agriculture and Allied
sciences
Soil Acidification and Lime Quality: Sources of Soil Acidity, Effects on Plant
Nutrients, Efficiency of Lime and Liming Requirements.
Athanase Nduwumuremyi*
Natural Resources Management, Rwanda Agriculture Board, Rwanda.
Review Article
Received: 01/09/2013
Revised : 22/09/2013
Accepted: 03/10/2013
*For Correspondence
Natural Resources
Management, Rwanda
Agriculture Board, Rwanda.
Keywords: Al toxicity; Crop
response; Soil pH; Lime purity;
Lime requirement; Lime
solubility
ABSTRACT
Agriculture sectors support economy of most developing countries.
In Sub-Sahara Africa, the agriculture is predominantly based on rain-fed
agricultural production of small, semi-subsistence, and increasingly
fragmented farms. Thus, the farming is intensive and fields are
concentrated on valleys, steep hillsides and mountains. This results in soil
acidity, low fertility, accelerated soil erosion and low crop yields. Soil acidity
affects crops in many ways and its effects are mostly indirect, through its
influence on chemical factors such as aluminum (Al) and manganese (Mn)
toxicity, calcium (Ca), phosphorus (P) and magnesium (Mg) deficiencies and
biological processes. The application of lime believed to enhance soil
health status through improving soil pH, base saturation, Ca and Mg. It
reduces Al and Mn toxicity and increases both P uptake in high P fixing soil
and plant rooting system. However, the liming effects depend on its source,
its characteristics, composition, purity and how finely it is crushed. In
addition, the constraints of estimating lime requirement limit its use for
smallholder farmers. This review therefore aimed at highlighting the most
causes of soil acidification, and provides important formulas to calculate
lime requirement and evaluate its effects.
INTRODUCTION
Agriculture sector is the economy pillar of most developing countries. However, agricultural productivity
remains critically low in most of these countries. The low productivity of the agricultural sector is largely attributed
to low and decreasing soil fertility due to many factors such as soil acidity, soil erosion, continuous cropping and
inadequate sustainable soil fertility management [1,2,3,4]. For instance, the acidity affects the fertility of soils through
nutrient deficiencies (P, Ca and Mg) and the presence of phytotoxic nutrients such as soluble Al an d Mn. Application
of lime reduces Al and Mn toxicity, improves pH, Ca, Mg and increases both P uptake in high P fixing soil and plant
rooting system [5]. The use of lime is a potential option for soils sustainable management among the other options
for restoring soil health and fertility. In agriculture, the limes play a great importance in improving soil acidity and
hence favour plant nutrition.
The lime is known as a material originated from rocks which can have multiple purposes (construction,
cement production, water purification, disinfectant, agricultural amendments...). Locally available carbonates are
relatively common in many countries of sub-Saharan Africa and are well suited for small-scale mining and
processing [2]. However, due to the bulkiness of lime, the capacity to produce and supply enough lime in
affordability manner (cost effectiveness) is very low. In sub-Sahara Africa, lime production rely on traditional
techniques without appropriate machines for finely grinding limestone, consequently, limes produced are less
effective and therefore, are very expensive as they are needed in high quantity [6] to meet the requirement in the
soils.
The use of lime and its requirement depends on the level of acidity in the soils. Some of limiting factors to
widespread use of lime in many areas of sub-Saharan Africa are; lack of awareness among farmers on its use, lack
of appropriate recommended rates, and high cost and unknown quality of the available agricultural limes.
Furthermore, knowledge on the effectiveness of various lime sources in correcting soil acidity is lacking due to
limited studies done in the region. Information on causes of soil acidity, lime quality, effectiveness of lime in

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reducing soil acidity and in improving crop yields is vital in lime selection and formulation of recommendations
rates that are necessary for spurring farmer uptake of the liming technology. The young soil scientists need
therefore a concise guide for determining lime requirements. This review article is presenting the causes and forms
of soil acidity and some formulas and guide for lime requirement determination.
Soil pH and acidification
Soil pH is a measure of the number of hydrogen ions in the soil solution; the higher the concentration of
hydrogen ions, the more acidic the solution is. Understanding soil pH is essential for the proper soil management
and optimum crop productivity. In aqueous (liquid) solutions, an acid is a substance that donates hydrogen ions
(H+) to some other substance [7]. Soil pH is an excellent chemical indicator of soil quality. Theoretically, soil acidity is
quantified on the basis of hydrogen (H+) and aluminium (Al3+) concentrations of soils [8].
Soil acidity occurs when there is a build-up of acid forming elements in the soil. The production of acid in
the soils is a natural process; caused by rainfall and leaching, acidic parent materials and organic matter decay [9]
hence many soils in high rainfall areas are inherently acidic [10]. Acidification is a slow process but it is accelerated
by agriculture through; use of some fertilizers, soil structure disturbance and harvest of high yielding crops [8]. As
soils become more acidic, plants intolerant to acidic conditions are negatively affected leading to productivity
decline. The aim of attempting to adjust soil acidity is to neutralize pH and Al toxicity but the most important is to
replace lost cations nutrients, particularly calcium and magnesium [8]. This can be achieved by adding limestone to
the soil [11] and farmers can improve the soil quality of acidic soils by liming to adjust pH to the levels needed by the
crop to be grown.
Soil acidification and Aluminium toxicity
Soils become acidic for several reasons. The most common source of hydrogen is the reaction of
aluminium ions with water. Aluminium toxicity in combination with low pH [12] is one of the major reasons that
render acidic soils unsuitable for the growth of many plants in the humid tropic countries. The forms of aluminium
ions present vary with pH [8]. The increased soil acidity causes solubilisation of Al, which is the primary source of
toxicity to plants at pH below 5.5 [13]. As observed by Carson and Dixon [14], under very acidic conditions of pH less
than 4.5, the major form of aluminium is Al3+, and pH between 4.5- 6.5, aluminium-hydroxyl dominates. As the pH
increases, exchangeable Al3+ precipitates as insoluble Al hydroxyl forms at a rate of 1000 fold decrease for each
unit increase in pH (equation 1).
Al3+ + H2O Al OH2 + H+ Equation (1)
The equation (1) explains the reaction of aluminium-hydroxyl in very acid soils. However, at pH greater than
6.5, aluminium becomes increasingly soluble as negatively charged aluminates form [15]. The heavy rainfall can also
contribute to the soil acidification by natural causing parent materials to be acidic due to leaching of cations [16].
There are other important causes of soils acidification, such as, ammonium fertilizers, release of organic acids in
decomposition of crop residues or organic wastes [17] and continuous cultivation of legumes [18]. The acidification
caused by the use of ammonium fertilizers are explained by the release of H+ (equation 2).
NH+4+ 2O2NO3+ H2O + 2H+ Equation (2)
The acidification due to legumes is explained by higher absorption of basic cations of legumes and the
release of H+ ions by the root of legume crops to maintain ionic balance, and during N2 fixation through a function
of carbon assimilation [18].
Soil acidity and base saturation and buffering capacity
A relatively high base saturation of CEC (70 to 80%) should be maintained for most cropping systems,
since the base saturation determines in large measure the availability of bases for plant uptake, and strongly
influences soil pH as well. Low base saturation levels results in very acid soils and potentially toxic cations such as
Al and Mn in the soil. A high base saturation (>50%) enhances Ca, Mg, and K availability and prevents soil pH
decline. Low base saturation (<25%) is indicative of a strongly acidic soils that may maintain Al3+ activity high
enough to cause phytotoxicity [19].
The resistance of soils to changes in pH of the soil solution is termed buffering. In practical terms, buffering
capacity for pH increases with increase in the amount of clay and organic matter [19]. Thus, soils with high clay and
organic matter content (high buffer capacity) will require more lime to increase pH than sandy soils with low
amounts of organic matter (low or weak buffering capacity).

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Soil acidity and crop responses
Soil pH affects crops in many ways and its effects are mostly indirect, through its influence on chemical
factors and biological processes. Chemical factors include aluminium (Al) toxicity, calcium (Ca) and phosphorus (P)
and magnesium (Mg) deficiencies [20]. Optimum nutrient uptake by most crops occurs at a soil pH near 7.0. The
nutrients availability such as nitrogen, phosphorus and potassium is generally reduced as soil pH decreases.
Phosphorus is particularly sensitive to pH and can become a limiting nutrient in strongly acid soils. Thus, reduced
fertilizer use efficiency and crop performance can be expected when soil acidity is not properly controlled [21]. Hardy
et al. [22] reported exchangeable Al to affect crops (Table 1) by shallow rooting, poor use of soil nutrients, and Al
toxicity.
Table 1: Crops tolerance to Al saturation
Main crops
Al Saturation (Al/ECEC)
Adjustment options
Beans
0
Lime and fertilizers
Maize
<0.4
Lime and fertilizers
Irish potato
<0.5
Lime and fertilizers
Cassava
0.2-0.5
Lime and fertilizers
The application of lime showed to increase the overall production of various crops. The previous studies
done oh different crops demonstrated that when only 1 ha-1 of lime applied in cassava, there was a yield increase
of 12.6t ha-1. The lime rate of 4t ha-1 applied in the field of beans, Irish potato and maize, the yield increase were
1.27t ha-1, 10t ha-1 and 1.4t ha-1, respectively (Table 2).
Table 2: Effects of lime on yield of some main crops
Crops
Exchangeable Al
(cmol kg-1)
Lime applied (t
ha-1)
Yield
(t ha-1)
References
Beans
2.9
0
1.03
[23]
Beans
2.9
4.4
2.3
[23]
Maize
2.13
0
2.2
[24]
Maize
2.13
3.2
3.6
[24]
Potato
2.8
0
14
[25]
Potato
2.8
4.2
24
[25]
Cassava
1
0
17.74
[26]
Cassava
1
1
30.34
[26]
Liming is an important practice to achieve optimum yields of all crops grown on acid soils. Application of
lime at an appropriate rate brings several chemical and biological changes in the soils, which are beneficial or
helpful in improving crop yields on acid soils (Figure 1 and 2). Plant growth improvement in acid soils is not due to
addition of basic cations (Ca, Mg), but because of increasing pH reduces toxicity of phytotoxic levels of Al [4, 27].
Potato needs heavy amounts of fertilizers and tuber yields are seriously affected in soils with shortages of
P and K. Yamoah et al. [28] found that Potato yield can be significantly increased by residual lime. Potato yields at
lower lime differed from those at the higher rates by about 30%, again substantiating a much longer residual effect
with the use of higher rates [29]. Hester [30] reported 25 to 29% increase in potato yield due to small applications of
lime on soil with a pH of 5.2. Plant nutrients are most available at soil pH levels near 6.5; Potatoes grown in soils
near pH 6.5 produce higher yields with less fertilizer [31]. The ideal pH for Potato ranges from 5.2 to 6.5 [32]. The
beneficial effects of liming on crop growth are often related to neutralization of Al and not directly to the change in
pH.
Liming and its advantages in acidic soils
Liming is an important practice to achieve optimum yields of all crops grown on acid soils. According to
Kaitibie et al. [33], liming is the most widely used long-term method of soil acidity amelioration, and its success is
well documented [34]. Application of lime at an appropriate rate brings several chemical and biological changes in
the soils, which are beneficial or helpful in improving crop yields on acid soils [8].
Liming raises soil pH, base saturation, and Ca and Mg contents, and reduces aluminium concentration in
acidic soils [35]. The acidic soils are naturally deficient in total and plant available phosphorus. This is because
significant portions of applied P are immobilized due to precipitation of P as insoluble Al phosphate or
chemisorptions to Al oxide and clay minerals [36]. The liming of acidic soils result in the release of P for plant uptake;
this effect is often referred to as ‘‘P spring effect’’ of lime [18]. Increase in availability of P in the pH range of 5.0 to

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6.5 is associated with release of P ions from Al and Fe oxides, which is responsible for P fixation [37]. But at high pH
(> 6.5) soluble P precipitate as Ca phosphate [38].
Soil microbiological properties can serve as soil quality indicators. Soil acidity restricts the activities of
beneficial microorganisms, except fungi, which grow well over a wide range of soil pH [39]. Liming acidic soils
enhance the activities of beneficial microbes in the rhizosphere and hence improve root growth by the fixation of
atmospheric nitrogen because neutral pH allows more optimal conditions for free-living N fixation [40]. It can also
suppress pathogens and producing phytohormones; enhancing root surface area to facilitate uptake of less mobile
nutrients such as P and micronutrients and mobilizing and solubilising unavailable nutrients [16 ].
According to McBride [41], increasing soil pH through liming can significantly affect the adsorption of heavy
metals in soils. Soil properties such as organic matter content, clay type, redox potential, and soil pH are
considered the major factors that determine the bioavailability of heavy metals in soil [42]. Hence, liming certainly
helps in reducing availability of heavy metals to crop plants.
Soil acidity is also responsible for low nutrient use efficiency by crop plants. Fageria and Baligar reported
that liming acidic soils improved the use efficiency of P, and other micronutrients by upland rice genotypes. In this
study, efficiency of these nutrients was higher under a pH of 6.4 than with pH 4.5. The liming improves efficiency of
nutrients through soil acidity management for improving their availability, and enhanced root system [43].
Calcium released from applied lime in soil has been reported to enhance plant resistance to several plant
pathogens [8], including Erwiniaphytophthora, R. solani, Sclerotiumrolfsii, and Fusariumoxysporum. Haynes [15]
reported that calcium forms rigid linkages with pectic chains and thus promotes the resistance of plant cell walls to
enzymatic degradation by pathogens. Therefore, liming provides calcium, which can contribute to build up plant
resistance to some pathogens.
Finally, liming has been promoted as mitigation option for lowering soil N2O emissions when soil moisture
content is maintained at field capacity [44]. Since soil pH has a potential effect on N2O production pathways, and the
reduction of N2O to N2, it has been suggested that liming may provide an option for the mitigation of N2O emission
from agricultural soils [45].
Sources of liming materials in sub-Sahara Africa
Almost all deposits of limestone in sub-Sahara Africa (SSA)are located in axis zones of N 35o E, this axis is
the one of recent major fracture related to the genesis of African rift valley [46]. Thus, there are large mines of
limestone (travertine and dolomite rocks) in SSA and exploitation of the main deposits is possible [23]. Liming products
(ground limestone and more or less burned limes) are at present almost exclusively produced in large quantity in some
countries of SSA. Although, limestone (travertine and dolomite) mines are abundant in SSA, only 30 % are coherent
rocks, required for the production of lime [23, 2]. The remaining 70 % occur as loose sandy travertine, which is not
suitable for lime production for construction. From an agronomic and economical point of view, it would be logical
to reserve the coherent rock fraction for lime production for construction and to exploit the sandy fraction for
agricultural purposes, using a more simple and low cost treatment. Very often, there is more variation in the CaO
and MgO content of local limes of the same deposit, as compared with travertine of different deposits. Therefore,
there is need for local lime mines which are capable of homogenizing the mixture of local lime.
Limestone of travertine group
Travertine is limestone with high Ca content (CaO>40%) and low magnesium content (MgO<3%). Travertine
is found in recent formations of Pleistocene age and is a less compact, soft rock, which is easily extractable without
explosives. Beernaert [23] reported that, travertine has a cationic (Ca/Mg) ratio of 13-15, which is much higher than
the optimal ratio of 4-5. This can cause disequilibria in the cation balance and affect soil fertility [23]. Kayonga and
Goud [47] observed that ground travertine rocks raised soil pH by 0.5 units, reduced exchangeable Al, increased
base saturation, and introduced disequilibria between the exchangeable cations. These rocks have a suitable
chemical composition to eliminate aluminium toxicity in acid soils but cause nutrient imbalance and hence create
new problems.
Limestone of dolomite group
A dolomite rock is limestone with high content of magnesium (CaO 30%, MgO 20%). The dolomite rocks of SSA
include dolomite limestone, dolomite marbles and dolomites. These are hard rocks used for building and construction
and which need explosives and more sophisticated cutting, drilling and grinding equipment, for their extraction.
Although records show the existence of very large reserves of dolomite deposits in SSA [48], very little is known about
their agronomic efficiency. The report by Wouters and Gourdin [49] showed that dolomite rocks can successfully

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eliminate soil acidity and Al toxicity but their chemical composition with a cation (Ca/Mg) ratio close to 1 is not suitable
for agriculture.
Solubility and qualities of lime
Lime is lowly soluble in water, so particles must be finely ground to neutralize soil acidity for a reasonable
period of time. Even very small changes in the sizes of the particles have a major effect on the time required to
dissolve them. Effectiveness depends on the purity of the liming material and how finely it is ground. The purity of
lime is rated by a laboratory's measurement of a Calcium Carbonate Equivalent (CCE). The lower the CCE value, the
more lime you will need to neutralize the soil's acidity [50]. When lime (e.g., CaCO3) is added to a moist soil, the
following reactions will occur:
Lime is dissolved (slowly) by moisture in the soil to produce Ca2+ and hydroxide (OH–):
CaCO3+ H2O in soil Ca2+ + 2OH  + CO2gas Equation (3)
Newly produced Ca2+ will exchange with Al3+ and H+ on the surface of acid soils:
Ca2+ +Soil particle + Al3+ and H+Soil particle + Ca2+ + Al3+ + H+ Equation (4)
Lime produced OH– will react with Al3+ to form solid Al (OH-)3, or it will react with H+ to form H2O as shown in
equations 5 and 6.
3OH+ Al3+ Al OH3solid Equation (5)
OH+ H+H2O Equation (6)
Thus, liming eliminates toxic Al3+ and H+ through the reactions with OH–. Excess OH– from lime will raise the
soil pH, which is the most recognizable effect of liming. Another benefit of liming is the added supply of Ca2+, as well
as Mg2+ if dolomite [Ca, Mg (CO3)2] is used. Calcium and Mg are essential nutrients for plant growth, yet they are
often deficient in highly weathered acid soils [20].
Efficiency of liming materials
Quality of liming material is very important in correcting soil acidity. The source of lime, its characteristics,
composition and the purity of lime are very important parameters for effective use of lime [51]. The efficacy of liming
materials is a key factor in determining its utilisation as profitable crop yield must be realised. The efficiency of a
liming material is determined by its acid neutralising potential, particle size distribution, availability and
convenience of spreading [52].
Many terms are used when describing the efficiency of liming materials, and commonly used terms are
relative neutralizing value (RNV), effective neutralising value (ENV) and effective calcium carbonate equivalence
(ECCE). The most methods for determining the quality and efficiency of liming materials are based on the
neutralising value (NV) and particle size distribution and various formulas have been developed. The NV is
determined by the chemical composition and the mineralogy of the liming material and is a measure of the amount
of acid neutralising compounds expressed as the percentage of calcium carbonate equivalence (CCE), with pure
calcium carbonate rated 100%. The efficiency of liming material is determined by its effective calcium carbonate
equivalence (ECCE), an estimation of the effectiveness represented as percentage and is the product of CCE and
the fineness factors of the various particle size fractions [53]. The key factors in determining the efficiency of liming
materials are its chemical composition and particle size distribution (Table 3).
Table 3: Particle size and efficiency factors of limes
Particle size(mesh sieving size)
Opening size(mm)
Efficiency factor
>8
>2.36
0
8-60
2.36-0.25
0.5
<60
<0.25
1.0
Source: Halvin et al.[9]
In addition to the efficiency of a liming material, its efficacy (amount of material required to adjust soil pH
to the desired level for profitable crop production) depends on the liming potential of the material, initial soil pH,
clay content and buffer capacity of the soil [53].

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Studies on the effect of particle size on soil pH and crop yield have shown that liming with finer liming
materials results in increments in soil pH over shorter time periods, and generally higher soil pH and crop yields [54].
The degree of fineness indicates the speed with which lime materials will neutralize soil acidity. Fineness is
measured by the proportion of processed agricultural lime which passes through a sieve with an opening of a
particular size. A 60-mesh sieve, which is the standard for comparisons of lime fineness and efficiency rating of
100%, is assigned [55].
Lime application
Methods, frequency, depth, and timing of liming are important practices in improving liming efficiency and
crop yields on acidic soils. To get maximum benefits from liming or for improving crop yields, liming materials
should be applied in advance of crop sowing and thoroughly mixed into the soil to enhance its reaction with soil
exchange acidity. The best method is broadcasting it as uniformly as possible and mixing thoroughly through the
soil profile. Liming frequency is mainly determined by intensity of cropping, crop species planted, and levels of Ca2+,
Mg2+, Al, and pH in a soil after each harvest. The effect of lime is long lasting but not permanent [8]. When values of
exchangeable Ca2+, Mg2+, and pH fall below optimum levels for a given crop species, liming should be repeated.
Effects of lime do last longer than those of most other amendments. However, it is rarely necessary to lime
more frequently than every 3 years [55]. The residual effect of coarse lime material is greater than with finer lime
material because large lime particles react slowly with soil acidity and tend to remain in the soil longer. A
reasonable depth of 20cm is required. Timing of lime application is important in achieving desirable results. Lime
should be applied as early as possible before planting of crop to allow it to react with soil colloids and to bring about
significant changes in soil chemical properties. Soil moisture and temperature are determining factors for lime to
react with soil colloids. In oxisols, significant chemical changes can take place 4–6 weeks after applying liming
materials so long as soil has sufficient moisture [56]. Hence, to obtain desirable results, it is not necessary to wait for
a longer period of time after applying lime.
Lime requirement
According to Soil Science Society of America [57], lime requirement is defined as the amount of liming
material, as calcium carbonate equivalent, required to change a volume of soil to a specific state with respect to pH
or soluble Al content. However, in economic terms, lime requirement can be defined as the quantity of liming
material required to produce maximum economic yield of crops cultivated on acid soils. Practically, different
approaches are available in order to predict the limestone rate required to attain an adequate level aiming to avoid
Al toxicity towards plant growth. One of the methods for predicting the lime requirement is to monitor the evolution
of exchangeable Al. The base enrichment especially of Ca2+ ions in soil will neutralize exchangeable Al thus
enhancing root growth [58]. Hakim et al. [59] reported that the optimal lime rate to improve some food crops planted
in the Ultisol is 6 tons CaCO3 per ha, then, over liming will occur at doses exceeding 12 tons per ha. Many
extracting solutions have been proposed to estimate the extractable Al and still KCl predominates [60]. The non-
readily exchangeable Al is estimated to be associated with organic matter, interlayer Al, and hydroxy-Al polymers
that contribute to the active acidity in the soil solution.
Lime requirement is determined following different methods. However, in this study the method described
by Kamprath [61] is the one seems to be easy applicable in most of weathered soils of sub-Sahara Africa. It has
ability to neutralize all extractable Al in soil. This method neutralizes exchangeable Al in the soil at the rate of 85-
90% [23] and has been applied successfully in different countries [62].The calculation of lime rates (LR) needed for a
given any type of lime is done through the following equation.
LR = Amount of pure lime
Calcium carbonate equivalent (any type lime) x100 Equation (7)
Table 4: Soil acidity and respective lime requirement
Soil pH
Soil exchangeable Al
(cmol kg-1)
LR (t ha-1) for first application*
>5.4
0-1
0-1.5
5.1-5.4
1-2
1.5- 3
5.1-4.7
2-3
3-4.5
≥4.7
≥3
≥4.5
LR: Lime requirement, LR (t CaCO3 ha-1) = Factor x Al cmol kg-1)

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The factor depends on the amount of organic matter in the soil (Table 5). For soils with 4 to 5% organic
matter content, lime application rates should be increased by 20 % [63]. In this study, the organic matter was rough
estimated at < 2.5%.
Table 5: Factors used to determine lime requirement
Factor
Organic matter (%)
extractable Al (cmol kg-1)
1-1.5
< 2.5
1
1.5-2
2.5-4
1
2
> 4
1
Source: adapted from Crawford et al.[4]
Determination of agronomic and economic effects of lime
The agronomic and economic effects of limes are determined by calculating the ratio of total yield from
limed and non-limed plots [64]. The relative agronomic efficiency (RAE) and relative economic efficiency (REE) of
limes is calculated to determine efficiency of lime. RAE and REE are calculated using the following equation.
REE (%) = Benefit - Cost (lime plots lime)
Benefit (control plot) *100 Equation (8)
RAE(%) = Yield (lime plots lime)
Yield (control plot) *100 Equation (9)
In the REE formula, the benefit and cost are those related solely to the liming cost .
CONCLUSION
Soil acidity associated to Al toxicities, soil erosion and soil nutrient depletion are the main soil related
constraints to agricultural development in parts of developing countries relying on agricultural to feed their growing
population. The smallholder farmers possess small sizes of land and are resource poor and have difficulties in
managing acidic soils. The potentials of using lime for soils sustainable management are among the other options
to explore in restoring soil health and fertility. In agriculture, the limes play a great importance in improving soil
acidity and hence favour plant nutrition. However, both farmers and most of young soil scientists facing the
challenges of estimating lime requirement for appropriately addressing soil acidity prevalence in most weathered
tropical soils. The knowledge of soil acidification sources serve as the guide in determining the forms of acidity to
address. In addition, lime requirement calculation is of help tool in avoiding under or overliming acidity soils which
are detrimental and compromising soil health and plant growth in general. Therefore, there is a need of advocating
the use of lime in proper manner and take precaution before liming any acidic soils.
ACKNOWLEDGEMENT
The authors are grateful to the Alliance for Green Revolution in Africa (AGRA) for financing integrated soil
fertility management (ISFM) in Africa. Gratitude is also expressed to the Rwanda Agriculture Board (RAB), Kenyatta
University (KU) and Higher Institute of Agriculture and Animal Husbandry (ISAE) for facilities provided during this
research work.
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