Soil Chemistry and Fertility
Soil chemistry and fertility examine the chemical reactions of the soil solution and solid surfaces that store and release nutrients, and the capacity of soil to supply the elements plants need to grow.
Definition
Soil chemistry is the study of the chemical composition, reactions, and processes of soils, especially at the interfaces between soil solids, water, and air; soil fertility is the capacity of a soil to supply essential nutrients in adequate amounts and balance for plant growth.
Scope
This area covers the charged colloids and cation exchange that retain nutrients, the acidity and pH that govern chemical availability, the cycling and supply of plant nutrients, and the chemistry of salt-affected soils. It links the molecular reactions at soil surfaces to the practical question of how productive a soil is, qualified as soil chemistry to distinguish it from environmental chemistry more broadly.
Sub-topics
Core questions
- How do charged soil colloids retain and exchange nutrient ions?
- How does soil pH control the availability of nutrients and toxic elements?
- How are plant nutrients cycled, stored, and supplied in soil?
- What makes saline and sodic soils chemically and physically problematic?
Key concepts
- Soil colloids and surface charge
- Cation exchange capacity and base saturation
- Soil pH and buffering
- Essential plant nutrients
- Nutrient availability and sorption
- Salinity and sodicity
Key theories
- Cation exchange capacity
- Negatively charged clay and organic colloids hold exchangeable cations that are reversibly available to plants and the soil solution, so cation exchange capacity is a master variable for nutrient retention and buffering.
- pH control of nutrient availability
- Soil pH governs the solubility and form of nutrients and potentially toxic elements; most nutrients are most available near neutral pH, while strong acidity or alkalinity reduces availability and can release toxins such as aluminium.
- Nutrient cycling and supply
- Plant nutrients move among mineral, organic, exchangeable, and solution pools through weathering, mineralization, sorption, and uptake, and soil fertility reflects the size and dynamics of these pools.
Clinical relevance
Soil chemistry and fertility underpin fertilizer and lime recommendations, the diagnosis of nutrient deficiencies and toxicities, the reclamation of acid, saline, and sodic soils, and the protection of water quality from nutrient losses; they are the scientific basis of soil testing and nutrient management.
History
Soil chemistry grew from 19th-century studies of cation exchange and Liebig's recognition that plant growth depends on mineral nutrients, through 20th-century work on colloid chemistry, pH, and nutrient cycling, into a quantitative discipline linking surface reactions to fertility and environmental quality.
Key figures
- Donald L. Sparks
- Nyle C. Brady
- Ray R. Weil
Related topics
Seminal works
- brady2016
- sparks2003
Frequently asked questions
- What makes a soil fertile?
- A fertile soil supplies the essential nutrients plants need in adequate amounts and balance, holds and releases them through cation exchange and organic matter, has a pH that keeps nutrients available, and is free of toxic levels of salts, sodium, or aluminium.
- Is soil fertility the same as soil health?
- No. Fertility focuses on the chemical supply of nutrients, while soil health is broader, also encompassing physical structure and biological activity; a soil can be chemically fertile yet degraded in structure or biology, or vice versa.