KP-152 · Soil Science & PQNK System
Understanding Soil Water Absorption: Composition, Gusra Soil, and a Field Test for Field Capacity
Explains how soil composition and pore size govern water infiltration and holding capacity, defines the locally significant 'Gusra' soil fraction, and provides a simple steel-pipe field test farmers can use to measure their own field capacity.
Read or listen to the full paper ↓Abstract
This paper explains soil water absorption as a function of the balance among sand, silt, clay, and organic matter, and specifically of pore size, which determines field capacity, the amount of water soil can hold. It stresses that this balance breaks down when soil is compacted or when mineral particles are poorly distributed, regardless of the underlying texture.
A locally significant fraction called 'Gusra,' a mineral particle size smaller than silt but larger than clay, is defined and flagged as a common regional factor that reduces water infiltration capacity, particularly when combined with low organic matter, even in soil that isn't compacted.
Diverse cover cropping (legumes, grasses, radishes) is presented as the structural fix: varied root architectures at different soil depths enlarge pores, increase field capacity, and reduce standing water, improving both absorption and holding capacity simultaneously.
The paper provides a specific, reproducible field-capacity test: press a 6-inch diameter, 12-inch long steel pipe vertically into the soil, pour in one liter of water, and time its absorption with a stopwatch, then repeat with a second liter to confirm the reading. This is offered as a practical, equipment-light way for farmers to benchmark their own soil rather than relying on generic guidance.
Full Paper
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Introduction to Soil and Water Absorption
• Soil is a mix of sand, silt, clay, and organic matter. The right balance of these components, when not compacted, allows soil to absorb and retain water effectively.
• Water is absorbed by soil through available pores, and pore size determines how much water the soil can hold (field capacity).
• Soil is made of sand, silt, clay, and organic matter. When balanced and not compacted, it holds water in tiny pores. The size of these pores determines how much water soil can store, known as field capacity.
Healthy soil structure is critical for water retention and crop growth. Diverse crop root establishment and retention play an important role where mineral particles in soil are not balanced, collapsed, or have small pores.
What is "Gusra" Soil? Fine Silt - Gusra soil
What is "Gusra" Soil?
• “Gusra" is a local term for a mineral particle smaller than silt but larger than clay. It affects soil structure and water absorption.
• Gusra soil with low organic matter has reduced water infiltration capacity, even when not compacted.
Gusra soil, a local term for particles smaller than silt but larger than clay. Gusra affects how water moves through your fields. If your soil has low organic matter or is compacted, it struggles to absorb and infiltrate water.
Gusra is common in some regions and impacts water movement. Emphasize the need for organic matter to improve structure.
Diverse Cover Crops for Better Soil Health
• Growing diverse cover crop species creates a varied root network at different soil depths, enlarging pores and improving water absorption.
• Diverse roots enhance soil structure, increase field capacity, and reduce standing water.
The solution? Plant diverse cover crops like legumes, grasses, and radishes. Their varied roots grow at different depths, opening up soil pores and boosting water absorption. This improves your soil’s structure, increases its water absorption and holding capacity, and reduces standing water.
Measuring Field Capacity
Measuring Field Capacity: To assess soil water absorption: 1.Use a 6-inch diameter, 12-inch long steel pipe. 2.Press the pipe vertically into the soil. 3.Pour 1 liter of water into the pipe and time absorption with a stopwatch. 4.Repeat with another liter to confirm field capacity.
• This method helps estimate how quickly soil absorbs water, guiding irrigation and soil management.
Want to know your soil’s water-holding capacity? Use a simple test! Take a 6-inch wide, 12-inch long steel pipe and press it into the soil. Pour in 1 liter of water and time how long it takes to absorb using a stopwatch. Repeat with another liter to confirm your soil’s field capacity.
Key Takeaways
• Soil composition (sand, silt, clay, Gusra, organic matter) determines water absorption.
• Hardpan reduces infiltration; diverse cover crops and organic matter improve it.
• Test field capacity to understand your soil’s needs.
• Visual Recommendation: Collage of healthy soil, cover crops, and a farmer testing field capacity.
Your soil’s mix of sand, silt, clay, Gusra, and organic matter controls how it holds water. Hardpan blocks water flow, but diverse cover crops and organic matter can fix this. Regularly test your soil’s field capacity to ensure healthy crops and better yields.
About This Paper
- Problem
- Poor Water Infiltration · Waterlogging · Low Soil Water-Holding Capacity (Field Capacity)
- Science
- Water · Soil
- Evidence
- Demonstration
- Authority
- Current / Approved PQNK Knowledge
Related PQNK Science
Key Takeaways
- Water absorption is governed by the balance of sand, silt, clay, and organic matter and by resulting pore size (field capacity), which collapses under compaction or poor particle distribution regardless of soil texture.
- 'Gusra,' a local term for particles smaller than silt but larger than clay, is identified as a common regional cause of reduced infiltration, especially when organic matter is low.
- Diverse cover crops (legumes, grasses, radishes) improve both infiltration and holding capacity by opening pores at multiple soil depths simultaneously.
- A simple field test is specified: a 6-inch diameter, 12-inch long steel pipe pressed into the soil, with 1 liter of water timed for absorption and a second liter to confirm the field-capacity reading.
- Hardpan is identified as the primary blocker of water flow regardless of composition; diverse cover crops and added organic matter are the corrective levers.
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