The document discusses soil acidity and its effects on plant nutrient availability. Key points include: - Soil acidity reduces the availability of many plant nutrients and can inhibit crop growth. Nutrient availability is optimal at a soil pH between 5.5-7.5. - Factors contributing to soil acidity include fertilizer use, organic matter removal, and natural soil properties. About 30% of global soils are acidic. - The document analyzes soil samples from Bangladesh which are acidic with high clay content. Nutrients like phosphorus are largely unavailable to plants in these acidic soils.

1. Impression of Soil Acidity on
Plant Nutrient Availability
Presenter : Md. Saiful Islam
ID No : 15606056
Session : 2014 – 15
Course No : Soil – 413 (Practical)
Grade : 4th Year B.Sc. (Hon’s)
Department of Soil Science
University of Chittagong

2. Outline….
Introduction
Objectives (Motivation)
Literature Review
Research Methodology
Experimental Result
Discussion
Limitations
Future Work
Conclusions

3. Many soils around the world have a natural tendency to become acidic with time. Many factors,
natural and managed, contribute to this increase in soil acidity. It is estimated that about 30% of
soils in the world are acidic.
Geo-morphologically acid sulphate soils, peat soils, acid basin clays, terrace soils and hill soils are
moderately to strongly acidic in reaction.
Contributing factors to acidity damage include its negative impacts on soil physical and biological
properties, high toxicities of elements like aluminum, iron, and manganese, and reduced
effectiveness of certain herbicides and availability of plant nutrients.
Research has proven that each crop develops better in a specific range of soil pH and that range
should also optimize nutrient availability. The chemical availability of several nutrients is
improved by liming acid soils.
In general, the availability of most nutrients is greatest in the soil pH range of 5.5-7.5.

4. Soil pH values (as measured in a water and soil solution) indicate:
• Strong acidity if less than 5.0.
• Moderate acidity at 5.0 to 6.0.
• Neutral between 6.5 and 7.5.
• Moderate alkalinity at 7.5 to 8.5.
• Strong alkalinity for values of 8.5 and above.
Causes of soil acidity:
1. The main cause of soil acidification is inefficient use of nitrogen, followed by the export
of alkalinity in produce.
2. Ammonium based fertilisers are major contributors to soil acidification. Ammonium
nitrogen is readily converted to nitrate and hydrogen ions in the soil.
3. Most plant material is slightly alkaline and removal by grazing or harvest leaves residual
hydrogen ions in the soil. Over time, as this process is repeated, the soil becomes acidic.

5. Acid soils are an alarming issue because of its adverse effect on soil fertility and
crop productivity. On soils where acidity slows crop development and reduces
yield.
Acid soils are caused by mining, potentially causing the death of plants. In our
country the amount of arable lands is degrading day by day due to soil acidification
which in turn result of inappropriate soil and crop management practice.
This study aims to report the current situation of acid soils and plant growth in
mine site and to elucidate the effects of acid soils on plant growth over time
through field investigation and a vegetation test.

6. Interactions between soil acidity and nutrient availability for plant growth have been widely reported;
however, most studies have been based on pasture species, and the agronomic importance of this
interaction for acid-tolerant wheat in soils with near-sufficient levels of fertility is unclear.
The application of lime showed to increase the overall production of various crops. The
previous studies done on different crops demonstrated that when only 1 t ha-1 of lime applied in
cassava, there was a yield increase of 12.6 t ha-1. The total requirement of lime to address the
problem of acidic soils in Rwanda was estimated at 2,200,000 tons for the first application and this
rate is not included in lime requirement for restoring soil health on newly terraces constructed.
Acidic sub-soils are usually accompanied by acidic surface soils but subsoil acidity is more
problematic for farmers because it is more difficult to neutralise it with lime. For acidic soils the
decreases of nutrients were modelled from relationships between soil pH, aluminium and manganese
solubility in different soil types, and plants’ susceptibility to toxicity from these elements
(Helyar2002). Acidity was considered to be a constraint when the decrease in yield (or yield gap) was
at least 5%.

7. Methods for Measuring soil pH:
1. One is an electrometric procedure for measuring pH in soils samples. In this method the sample is
mixed with reagent water, and the pH of the resulting aqueous solution is measured.
2. Another test method is the procedure for determining the pH of water or soil samples by use of a
pH meter.
Methods of Measuring Plant Available Nutrients:
1. Method to determine soil exchangeable calcium (Ca), magnesium (Mg), potassium (K), and
sodium (Na) by using atomic absorption spectrophotometer (AAS) and extraction with ammonium
acetate was applied.
2. The soil phosphorus contents extracted using the four different extraction methods were measured
using the Murphy and Riley colorimetric method and the results were correlated with the Olsen
method. The correlations were taken from the Regression analysis.

11. The sample soils from the different regions of Bangladesh were acidic in reaction indicating
the suitability of acid-tolerant crops, such as rice and wheat, in this region.
The soils were of medium- to heavy-texture, and textural classes were silt loam for four
soils, silty clay loam for other four soils and clay and clay loam for one each soil according
to the USDA system.
Most soils had considerable amounts of clay with a wide range of the content from 14.4 to
64.4%, and the variation was mainly related to the topographical position of soils on the
landscape. Chlorite was found as a dominant mineral in one soil and detected in small
amounts in other soils.
The results indicate that all soils were almost similar in the mineralogical composition. This
soil is located in medium highland and belongs to Acid Basin Clay in the general soil type.
Most of the soils of the present study had the moderate to high amounts of highly weathered
clays, which were dominated by mica and kaolinite minerals.

12. Constraints and Limitations have been identified through review of literature and also through analysis
of the soil samples.
1. Depletion of soil organic matter is a major constraint to higher crop production in Bangladesh that
leads to soil acidity. The organic matter level in soil is in declining trend in most soils. This is
especially true for high and medium high land.
2. Unbalanced use of fertilizers, minimum use of manure, increasing cropping intensity, nutrient
leaching and light textured soils have favoured the emergence of soil acidity and interns causes soil
acidity.
3. The crop production potential is limited in these area due to less availability of phosphorous and
toxicity of aluminum. The injudicious extraction of plant nutrients by growing crops without proper
replacement causes plant nutrient deficiency, soil organic matter depletion, increased toxicity and
soil compaction. This leads to deterioration in soil physical, chemical and biological properties.

13. There are wide opportunity to go for further study in the different regions of Bangladesh
regarding the various issues caused by soil acidity. Only half the portion of the work has
been done to bring enough data about soil acidity in Bangladesh. More study may be
required to understand the comprehensiveness of this soils.
So future work may include:
1. Is there any relationship between soil acidy and soil salinity? If yes, then what is the
quantitative measure?
2. Is soil salinity related to drought?
3. The relationship between soil acidity and the phosphorous availability in soil.
4. How the soil acidity problem can be solved using other amendment instead of lime?

14. The sample soils acidic in reaction, and have the medium to high clay content which is highly
weathered in nature. The clay fraction was dominated by mica and kaolinite, and kaolinite
was found to exist as a discrete phase and as an interstratified mineral with smectite. The
inherent potentiality of these soils in respect of crop production was considered as poor to
medium.
The available N and P content in the soils seems to be deficient for plant growth. As the soils
are highly acidic, the available P is obviously low as most of the P become fixed. Slightly
higher content of available K in the upper horizons of the pedons may be due to bio-cycling
of K. Very high amount of available sulpher in the soils possibly due to oxidation of pyrites
during flashing and flooding of the soils with rain water in the monsoon months. The high S
contents may be attributed to the presence of sulphuric horizon within the profiles which is
harmful to crops.