Basics of Soil Fertility
Soil Fertility: Definition and Importance
Soil Fertility Definition:
A study of the status and movement of nutrients in soil that affects crop production positively or negatively.
Key Concepts of Soil Fertility
Two Major Soil Nutrition Phenomena:
1. Soil Fertility:
The ability of soil to supply nutrients to crops.
2. Soil Productivity:
The ability of soil to produce crops.
All productive soils are fertile, but not all fertile soils are productive.
Principles of Soil Fertility
Two Major Statements About Soil Fertility:
The Law of Minimum:
Plant growth and yield are determined by the essential nutrient that is present in the least amount in the soil.
The Law of Diminishing Returns:
Once a growth-limiting factor is identified, increasing its supply will lead to increased plant growth and yield, but at a decreasing rate.
Elements in Plant Nutrition
Elucidation of Nutrient Status:
Deficient: Low levels of nutrients severely limit yield.
Critical Range: Nutrient concentrations below which adding more nutrients can positively affect yield.
Sufficient: Nutrient range where adding more does not influence yield.
Excessive/Toxic: High enough nutrient levels that reduce yield or growth.
Concepts to understand further:
Steenberg Effect: A drop in nutrient concentration inside plant tissues because the plant grows rapidly after being fertilized, even though it is actually healthier overall
Luxury Consumption:
Scenario where plants accumulate nutrients in amounts greater than required for optimal growth.
Soil Types and Fertility
Comparative analysis of soils A, B, and C in terms of:
Nutrient sufficiency, microbial activity, and moisture availability.
Soil fertility can be classified into three types:
A. Physical Fertility: Sufficieny nutrients, microbes present, not enough water.
B. Chemical or Nutrient Fertility: Sufficient nutrients, microbes present, wet soil.
C. Biological Fertility: Sufficient nutrients, sufficient soil moistures, sufficient soil air, OM=0%
Criteria of Nutrient Essentiality
Nutrient must be essential for plant growth, reproduction, and life cycle completion.
Nutrient must be irreplaceable in its function.
Nutrient must be a structural or functional molecule necessary to plants.
Total of 17 essential plant nutrients identified.
Nutrient Classification Based on Requirement
Plant nutrients categorized as follows:
Basic Elements (Structural Nutrients): C, H, O
Macronutrients (required in bulk):
Primary: N, P, K
Secondary: Ca, Mg, S
Micronutrients (required in minuscule amounts):
Fe, Zn, Cu, Mn, B, Mo, Cl, Ni
Notably, cobalt (Co) is also acknowledged as essential by some.
Functions of Essential Plant Nutrients
Nitrogen (N):
Fundamental element in all cells, essential for chlorophyll, and promotes vegetative growth.
Phosphorus (P):
Supports early root development, strengthens plants, and is a component of adenosine triphosphate (ATP).
Potassium (K):
Enhances plant resistance, regulates stomatal opening and closure.
Calcium (Ca):
Activates growth enzymes and is important for seed and root growth.
Magnesium (Mg):
Plays a role in chlorophyll production and in transporting phosphates within plants.
Sulfur (S):
Involved in seed formation and nodule development in legumes.
Micronutrient Functions:
Various roles including influence on enzyme activities, cell development, and maintaining oxidation-reduction potential in cells (Fe, Zn, Cu, Mn, etc.).
Chlorine (Cl):
Stimulates enzyme activity and affects carbohydrate metabolism.
Nickel (Ni):
Required in small amounts for certain nitrogen-fixing plants.
Summary of Nutrient Chemical Properties
Elements categorized by chemical properties:
Metals: K, Ca, Mg, Fe, Zn, Cu, Mn, Ni
Non-metals: C, H, O, N, P, S, B, Mo, Cl
Anions: N, P, Cl, Mo, B, S
Cations: K, Ca, Mg, Fe, Zn, Cu, Mn, Ni