Estimating Soil Moisture by Appearance and Feel

By N. Klocke and P. Fishbach http://www.p2pays.org/ref/20/1976 1.htm

Evaluate soil moisture

• Important management tools • How much to irrigate • When to irrigate • “appearance and feel” method • Where moisture is located in the profile • Depth of water penetration from irrigation or rainfall • ID problem areas soil compacted layers that restrict water penetration

Soil Texture

• Relative amount of sand, silt and clay • Indicates amount of water soil will hold • Available water capacity is max water the soil holds that plants can use

Available water capacity for soils Soil texture available water inches/foot Fine sand or loamy sand 1.0 to 1.1

Sandy loam 1.4

Loam or silt loam Silty clay or clay loam 2.0 to 2.5

1.8

Knowing water potential

• Different soil types respond differently to method described • Key is texture • County soil survey • Cooperative Extension Office or Natural Resource Conservation Service office

Sampling and Evaluation Procedures • Extract sample. Probe, auger, spade • One foot intervals • Surface to bottom of active root zone • Most crop – 3 feet • Start early in spring – 1 to 2 days after a heavy rain – Soil near field capacity • End of growing season – Soil is dry • Use photo descriptions

Guides for estimating soil moisture • Soil probe extract the sample – Scrape clean before inserting probe – Pull sample back to surface – Inspect soils, remove all soil – Clean probe after each use

Procedure using description

• Determine texture • Squeeze firmly • Observe condition of soil ball • Attempt to form a ribbon • Observe what happens • Compare your observations with photos and descriptions in guides

Use photo descriptions

• From http://mt.nrcs.usda.gov/technical/ecs/agronomy/ soilmoisture/sandyclay.html

• Sandy clay, loam and silt loam soils – Available water capacity = 1.5 to 2.1 inches per foot – % available : current available soil moisture as % of available water capacity – Inches per foot depleted: inches of water currently needed to refill a foot of soil to field capacity

0 to 25% available 2.1 to 1.1 inches per foot depleted • Dry, • soil aggregations breaks away easily, • no staining on fingers, • clods crumble with pressures

25% to 50% available 1.6 to 0.8 inches per foot depleted • Slightly moist • Forms a weak ball with rough surfaces • No water staining on fingers • Few aggregated soil grains break away

50% to 75% available 1.1 to 0.4 inches per foot depleted • Moist • Forms a ball • Very light staining on fingers • Darkened color • Pliable • Forms a weak ribbon between thumb and forefinger

75% to 100% available 0.5 to 0.0 inches per foot depleted • Wet • Forms a ball with well defined finger marks • Light to heavy soil/Water coating on fingers • Ribbons between thumb and forefinger

100% available 0.0 inches per foot depleted (field capacity) • Wet • Forms a soft ball • Free water appears briefly on soils surface after squeezing or shaking • Medium to heavy soil/water coating on fingers

Use photo descriptions

• From http://mt.nrcs.usda.gov/technical/ecs/agronomy/ soilmoisture/clay.html

• Clay, clay, loam and silt clay loam soils – Available water capacity = 1.6 to 2.4 inches per foot – % available : current available soil moisture as % of available water capacity – Inches per foot depleted: inches of water currently needed to refill a foot of soil to field capacity

0 to 25% available 2.4 to 1.2 inches per foot depleted • Dry, • soil aggregations separate easily, • Clods are hard to crumble with applied pressure

25% to 50% available 1.8 to 0.8 inches per foot depleted • Slightly moist • Forms a weak ball • Very few soil aggregations break away • No water stains • Clods flatten with applied pressure

50% to 75% available 1.2 to 0.4 inches per foot depleted • Moist • Forms a smooth ball with defined finger marks • Light soil/water staining on fingers • ribbon between thumb and forefinger

75% to 100% available 0.6 to 0.0 inches per foot depleted • Wet • Forms a ball • Uneven medium to heavy soil/water coating on fingers • Ribbons easily between thumb and forefinger

100% available 0.0 inches per foot depleted (field capacity) • Wet • Forms a soft ball • Free water appears on soil surface after squeezing or shaking • Thick soil/water coating on fingers • Slick and sticky

Calculating soil moisture status

• After estimating soil moisture, water can be calculated using table values • Example: silt loam – Available water at FC = 2.4 inches / foot – Current status = 50% available soil moisture remaining – Amount of soil in sample = 1 foot – Available moisture remaining = 50* 2.4 in/ ft * 1 ft = 1.2 inches

Other sites How to estimate soil moisture by feel • Why know available soil water?

– Management decisions • Favorable moisture, plant population, nutrients applied – Large acreages • Several day to cover area • Most crops start irrigation when 50% available moisture in root zone is depleted

Degree of soil moisture Dry Fair Percent useful soil moisture 0 50-75% Ideal Chart below from http://sanangelo.tamu.edu/agronomy/sorghum/moisfeel.htm

at FC Appearance of soils __________________ powdery, hard, baked, slightly crusted cracked__ forms a ball, somewhat forms a ball, will ribbon plastic_________________ squeezing, no free water appears, wet outline of ball left on hand

Knowing the texture and topsoil depth • Estimate available water – Soil texture is silt or clay loam • 1.5 to 2 inches of available water per foot – Soil texture is clay • 2-2.5 inches of available water per foot of topsoil