Field Capacity and water holding capacity of soil.pptx

The amount of water content held in the soil after excess water has drained away and the rate of downward movement has decreased. This occurs usually 2–3 days after a rain or irrigation.
The total amount of water that a soil can hold after being saturated and then drained by gravity.
Dependent on the soil’s texture and organic matter.
Clay soils have high WHC, while sandy soils have low WHC.
Influenced by porosity, structure, and soil compaction.
Clay Soils: These have fine particles and smaller pore spaces, allowing the soil to hold more water, have both high field capacity and water holding capacity.
Sandy Soils: With larger particles and larger pores, sandy soils drain quickly, less water is retained, have lower field capacity and water holding capacity.
Loamy Soils: Loam has an intermediate texture. It balances drainage and water retention, offering moderate FC and WHC, making it ideal for agriculture.
Water for plants:
Knowing how much water the soil can hold helps us ensure that plants have enough water to grow well.
2. Irrigation and water management:
Understanding FC and WHC helps farmers decide how much water to give their plants and when. This prevents wasting water by overwatering or letting plants dry out.
3. Healthy soil:
Soils with the right amount of water are less likely to suffer from problems like erosion or nutrient loss.
Protection during dry spells:
Soils with high water holding capacity can store more water and release it slowly to plants, helping them survive during droughts.
Preventing soil damage
Managing FC and WHC helps prevent soil from becoming damaged by too much water washing away nutrients or too little water causing it to dry out.

1. Field capacity and water holding capacity of soil

2. Field Capacity “The amount of water content held in the soil after excess water has drained away and the rate of downward movement has decreased. This occurs usually 2–3 days after a rain or irrigation.”

3. Types of water Role : Field capacity represents the amount of capillary water that remains in the soil after gravitational water has drained. This water is the most accessible to plants and supports healthy root growth.

4. Field Capacity Measurement Methods Gravimetric Method: Weighing soil samples before and after drying. Tensiometers: Measuring soil moisture tension. Neutron Probes: Determining water content by radiation scattering. Time-Domain Reflectometry (TDR): Using electric pulses to measure water content in soil.

5. Water Holding Capacity (WHC): “The total amount of water that a soil can hold after being saturated and then drained by gravity.” Dependent on the soil’s texture and organic matter. Clay soils have high WHC, while sandy soils have low WHC. Influenced by porosity, structure, and soil compaction.

6. Water forms included: Hygroscopic Water: Thin film around soil particles, held tightly by adsorption and not available to plants. Capillary Water: Held in smaller soil pores and is the primary water source available to plants. Gravitational Water: Water that occupies large soil pores and drains out of the soil profile under the influence of gravity. Hygroscopic Water Capillary Water Gravitational Water

7. Water holding capacity measurement methods Weigh and Dry Method
Centrifuge Method Pressure Plate Method

8. Soil water retention curve Sandy soils hold less water due to larger particles and larger pores. Clay soils hold more water but also retain more unavailable water. Loam soils have a balanced water holding capacity, providing a good mix of available water and drainage. % of Water uptake pH

9. Differences Between FC and WHC: FC refers to water content available to plants after gravitational water has drained, while WHC includes both available and unavailable water (water held too tightly for plants to absorb).
Field capacity is often a practical measure for understanding water availability for plants, whereas WHC is more about the soil’s overall potential to store water.

10. Factors Affecting Both FC and WHC: Soil Texture Clay Soils : These have fine particles and smaller pore spaces, allowing the soil to hold more water , have both high field capacity and water holding capacity. Sandy Soils: With larger particles and larger pores, sandy soils drain quickly, less water is retained , have lower field capacity and water holding capacity. Loamy Soils: Loam has an intermediate texture. It balances drainage and water retention, offering moderate FC and WHC, making it ideal for agriculture.

11. 2. Organic Matter: Organic matter improves the soil’s structure by binding particles together, which allow soils to retain more water, holding water in the root zone, especially useful in sandy soils where water drains quickly. Soils rich in organic matter have higher FC and WHC, as they can absorb more water and release it slowly to plants.

12. 3. Soil Structure Well-structured soils have a balanced mix of: Small pores hold water. Large pores aid drainage. Poor soil structure, often due to compaction or over-tillage, reduces: Water infiltration Water retention Soil aggregates improve: Aeration Water movement pathways Field capacity (FC) and water-holding capacity (WHC)

13. 4. Soil Compaction: Compaction lowers both FC and WHC by reducing the size and number of pores in the soil. It also hinders root growth. Compacted soils dry out quickly because water can’t infiltrate properly, leading to poor drainage and low water retention. Practices like heavy machinery use and overgrazing can lead to soil compaction. Normal soil Compacted Soil

14. Significances: Water for plants: Knowing how much water the soil can hold helps us ensure that plants have enough water to grow well. 2. Irrigation and water management: Understanding FC and WHC helps farmers decide how much water to give their plants and when. This prevents wasting water by overwatering or letting plants dry out. 3. Healthy soil: Soils with the right amount of water are less likely to suffer from problems like erosion or nutrient loss.

15. Significances Protection during dry spells: Soils with high water holding capacity can store more water and release it slowly to plants, helping them survive during droughts. Preventing soil damage Managing FC and WHC helps prevent soil from becoming damaged by too much water washing away nutrients or too little water causing it to dry out.

16. Significances Adapting to climate change As weather becomes more unpredictable, soils that can hold water better are more resistant to changes like droughts or floods. 7. Environmental benefits Proper water management reduces runoff, which prevents water pollution and soil erosion.
Soils that hold water well can also help refill groundwater supplies, which many people rely on for drinking and farming.