Soil Genesis and Plant Nutrition
Importance of Water in Soil Genesis and Plant Nutrition
Role of Water in Soil
Water plays a crucial role in soil genesis and plant growth. It is essential for:
- Soil formation processes
- Plant requirements like transpiration, cell elongation, and metabolism
- Nutrient transport during radical absorption
Properties of Water
Water is a bipolar molecule with an unevenly distributed electrical charge, despite being electrically neutral. Water molecules interact through hydrogen bonding, which is crucial for their unique properties.
Soil Water Energy Concepts
Understanding the energy status of soil water is essential for comprehending water retention, movement, absorption, and transport phenomena in plants. Free energy describes the energy state of water, indicating its tendency to change.
Forces Acting on Soil Water
Several forces influence water in the soil:
- Strength of the soil matrix
- Osmotic force
- Gravity
Field Capacity
Field capacity refers to the water content in the soil after free drainage. It represents the maximum available water level for plants.
Methods for Determining Soil Moisture
Direct Methods
- Cultural UP: Extracting soil from the field and separating water from the soil through drying.
Indirect Methods
- Gypsum Blocks: Based on electrical conductivity, where higher resistance indicates lower moisture content.
- Neutron Probe: Measures thermalized neutrons returning to the probe, indicating water content.
- Tensiometer: Determines the energy status of soil water.
- Psychrometer: Directly measures water potential.
Water Movement in Soil
Saturated Flow
Saturated flow occurs when soil pores are completely filled with water, driven by gravity. It typically takes 24 to 48 hours to reach equilibrium with the groundwater table. Macropores are primarily responsible for saturated flow, which is mainly vertical but can also occur horizontally to a lesser extent.
Unsaturated Flow
Unsaturated flow is more common in field conditions, where pores are partially filled with water. Capillary action and surface tension play significant roles in this type of flow. The hydraulic gradient, driven by moisture tension, is the primary force. Hydraulic conductivity decreases as soil moisture content decreases.
Factors Affecting Soil Moisture Availability and Use
Plant Factors
- Root habits
- Drought tolerance (moisture stress)
- Growth stage
Weather Factors
- Air temperature
- Humidity
- Wind speed
- Solar radiation
Soil Factors
- Soil moisture tension
- Water storage capacity of the profile
- Depth
- Layering
- Texture
Mechanism of Water Uptake by Plants
Plants absorb water through their roots by adjusting to the water film and creating a moisture tension gradient. Roots elongate towards areas of lower humidity. However, this behavior is debatable under field conditions, and the movement is limited. Irrigation is crucial to provide sufficient water for plant uptake.
Water Consumption and Use
Water consumption refers to the total amount of water used by a crop during its development, including evaporation from the soil surface and leaves, as well as transpiration. It depends on weather conditions and plant factors like root system, water use efficiency, and growth period. Water availability in the soil also influences consumption.
Potential Evapotranspiration
Potential evapotranspiration is the amount of water that would evaporate and transpire under given climatic conditions if there were no water limitations. It depends on plant, soil, and climatic factors, similar to water consumption. It correlates with pan evaporation.
Organic Matter in Soil
Principal Organic Compounds
The main organic compounds in soil include:
- Carbohydrates
- Lignin
- Nitrogen compounds
- PyS compounds
- Other compounds like waxes, fats, and resins
Importance of Soil Fauna
Soil fauna plays a vital role in:
- Maceration and grinding of plant debris
- Distribution of plant debris
- Contribution to soil aeration and drainage
Importance of Earthworms
Earthworms are particularly important for:
- Conditioning organic debris to enhance microbial decomposition
- Improving soil aeration and drainage
- Stabilizing soil structure
- Providing nutrients for plants
Humus
: comprising: sust not humitas ( soluble in ethanol), alkali-soluble humin, sub humitas comp. For ac and ac Humitech Fulvic content of organic mat varies according to climate, vegetation, topography, soil mat generator, age and soil management, Effect of physical prop: interperisacion mineral soil, improving soil aggregation and des radically improves the absorption of water and air cont soil decreases runoff water sup facilitates tillage Effect of chemical prop: a growing resistance to the rafters CICY ww Effect of soil biological prop phase out the development of soil organisms Preda nitrogen: not all the nitrogen is mineralized q leverage existing plants lost by immobilization by microorganisms lixibiacion, chemical transformations; bolatilizacion Nitrogen, Erotion and burn. Association between soil organisms and micro higher plants: Association risosfera level: the area of soil influenced by root exudates Azospirillum plant causes an increase in the number of root hair, the greater absorption of water and nutrients, besides fixing atmospheric N2. Micorificas Associations:Ectotroficas: they form a mantle of fungal mycelium in the roots and results in better absorption into the soil. Endotroficas: inside of the roots the fungal hyphae reach places out of reach of the roots channeling nutrients to higher speed (herbaceous)