Soil pH Lecture by Salman Saeed
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The document is an introduction to a course on plant physiology and ecology, specifically discussing the importance of pH in soil. It explains how pH levels influence plant growth and nutrient availability, noting the negative effects of low pH, such as toxicity from metals and impaired nitrogen fixation in legumes. Conversely, it highlights the impact of high pH on nutrient exchange and microbial activity.
![Introduction
pH is:
Measure of acidity or basicity
Defined as negative logarithm of activity of H+ ion in a
solution
pH = -log [H+].
pH ranges between 1-14.
Basic >7
Acidic <7
Neutral =7](https://image.slidesharecdn.com/soilph-220725053215-6b6e6be7/85/Soil-pH-Lecture-by-Salman-Saeed-3-320.jpg)
Soil pH Lecture by Salman Saeed
- 1. Course Title: Plant Physiology and Ecology Course Instructor: SALMAN SAEED Botany department UNIVERSITY college of management & Sciences, Khanewal, PAKSITAN
- 3. Introduction pH is: Measure of acidity or basicity Defined as negative logarithm of activity of H+ ion in a solution pH = -log [H+]. pH ranges between 1-14. Basic >7 Acidic <7 Neutral =7
- 4. pH Scale
- 5. pH The term "pH" was first described by Danish biochemist Søren Peter Lauritz Sørensen in 1909. “power of hydrogen” where “p” is short for the German word for power, potenz and “H” is the element symbol for hydrogen.
- 7. pH can affect nutrient availability by: formation of low solubility compounds, greater retention by soil colloids (clays and organic matter), conversion of soluble forms to ions that plants cannot absorb and Can inhibit or stimulate microbial activity.
- 9. Low pH Soil acidity affects plant growth in several ways: The concentration of soluble metals, especially aluminum and manganese may be toxic. Calcium may be deficient. When the soil pH is lower, more H+ ions are available to “exchange” base cations, thereby removing them from exchange sites and releasing them to the soil solution (soil water). Lower pH increases the solubility of Al, Mn, and Fe, which are toxic to plants in excess. A critical effect of excess soluble Alis the slowing or stopping of root growth. Low pH reduces the availability of the macro- and secondary nutrients
- 10. Symbiotic N fixation in legume crops is greatly impaired. The symbiotic relationship requires a narrower range of soil reaction than does the growth of plants not relying on N fixation. Populations and the activity of the organisms responsible to transform N, S, and P to plant-available forms may be reduced. The availability of mineral elements to plants may be affected.
- 11. High pH When the soil pH is high (i.e., more basic, low concentration of H+), more base cations will be on the particle exchange sites. As a result, exchanged nutrients are either taken up by the plant or lost through leaching or erosion. Microbial activity may also be reduced or changed.