BRAE236 - Lab5 Soil-Plant Moisture Lab

# BRAE236 - Lab5 Soil-Plant Moisture Lab - Basic Soil and...

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1 Basic Soil and Plant Water Definition of Terms (very quick review) Saturation Soil is filled with water with virtually no air pockets FC Field Capacity Upper limit of storable water in the soil once free drainage has stopped PWP Permanent Wilting Point Lower limit of storable water at which plants begin to irreversibly wilt

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2 Definition of Terms (quick review) AWHC Available Water Holding Capacity Water held between FC and PWP Expressed variously as (Inches of Water)/(ft of soil) Inches = (Inches of Water)/(ft of soil) × (root zone depth, ft) MAD Management Allowed Depletion % of the AWHC that is depleted before irrigating (managementdecision) SMD Soil Moisture Depletion inches of moisture depleted from field capacity. How many inches of water are required to fill the root zone up to field capacity Units % by volume * in water/in soil × 100 * cm water/cm soil × 100
3 25% Air 25% Water 50% Soil Solids Typical air-water-soil proportions of a typical loam soil at field capacity 25% by Volume = 3 in/ft 25% Air 25% Water Typical air-water-soil proportions of a typical loam soil at field Typical air water soil proportions of a typical loam soil at field capacity 25% by Volume Assuming the specific gravity of the soil solids is 2.65 gm/cm 3 , The oven dry weight in one cm 3 of bulk sample = .5 × 2.65 gm/cm 3 ×1 cm 3 = 1.32 gm The mass of water at field capacity = .25 × 1 cm 3 1 × gm/cm 3 = .25 gm % water by mass at field capacity = .25 gm/ 1.32 gm × 100 = 19%

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4 25% Air 25% Water 50% Soil Solids Typical air-water-soil proportions of a typical loam soil at field Typical air water soil proportions of a typical loam soil at field capacity 25% by Volume = 19% by mass For field applications, we are interested in VOLUME Soil science laboratories typically report water as % MASS % moisture by volume = Bulk Density × (% by Mass) where Bulk Density 1.65 gm/cm 3 for mineral soils Irrigation Scheduling When to irrigate?
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## This note was uploaded on 11/12/2011 for the course BRAE 236 taught by Professor Styles during the Spring '08 term at Cal Poly.

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BRAE236 - Lab5 Soil-Plant Moisture Lab - Basic Soil and...

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