Exam 2 Flashcards
Modules 5-8
What % of soil is water, air and soil solids?
25% water
25% air
50% soil solids
Range of Soil Moisture: Saturation
-all pore space is filled with water
-water will actively drain from soil due to gravity
Range of soil moisture: Field Capacity
-soil moisture that remains after excess water has drained
-some small air pockets in pore spaces
Range of soil moisture: Permanent Wilting Point (PWP)
-there is water in the soil, but it is so tightly adhered to soil particles that plants can’t access it
Range of soil moisture: Air Dry
-as dry as the soil can get when exposed to air
-a small amount of soil moisture remains
Range of soil moisture: Oven Dry
-no water left in soil
-all pore spaces filled with air
Available Water Holding Capacity (AWHC)
-amount of water available to plants
-AWHC= Field Capacity (FC) - Permanent Wilting Point (PWP)
Soil Moisture Content (SMC)
-amount of water that exists in soil at a particular time
-changes daily as plants take up water in their normal growth processes
-may be measured as % water by mass, % water by volume, or inches of water per foot of soil
Soil Moisture Depletion (SMD)
-amount of water that’s below field capacity
-SMD=FC-SMC
Management Allowed Depletion (MAD)
-% varies by crop/situation
-the percentage of available water holding capacity that management allows to be used up before irrigation
Maximum Soil Moisture Depletion (max SMD)
-the largest SMD is allowed to become before an irrigation
-SMD max= AWHC x MAD
How does soil effect water tension?
clay-highest soil water tension
silt-moderate soil tension
sand-low soil water tension
When is large MAD appropriate?
-hand move or wheel move sprinkler systems
-furrows and border strips with long runs or sandy soils
-specific plant requirements: moisture stress for almonds, citrus, cotton, wine grapes
When is small MAD appropriate?
-irrigation systems capable of small, frequent irrigations
-irrigation with saline (salty) water
-uncertain water supply
-specific plant requirements: root crops (carrots, onions and potatoes), stone-fruit (cherries, peaches), strawberries and corn
Properties of water
Cohesion- water molecules are attracted to each other
Adhesion- water molecules are attracted to others
Capillary Action- when liquid flows through narrow spaces without external forces like gravity
Polarity- unequal sharing of molecules
Why do humans modify the hydrologic cycle?
there is a limited amount of freshwater to accommodate to everyone’s needs
Evaporation
loss off water from evaporation from the surface of the soil or bodies of water
Runoff
water pools on soil surface and gathers in bodies of water
Infiltration
water seeps into the ground
Groundwater
water stored in the ground
Watershed
an area of land that channels rainfall, snowmelt, and runoff into a common body of water
Aquifer
a body of rock or sediment that holds groundwater
What is most water used for by humans?
Irrigation
What is the second largest use of water by humans?
Domestic
Where are aquifers located in CA?
-along the coastline
-one large aquifer in the San Joaquin Valley
Why is it an issue that the San Joaquin Valley shares an aquifer?
-no limits to amount of water being pumped
-too much water being pumped and not replenishing fast enough to make up for it
What is SGMA?
-the Sustainable Groundwater Management Act
-formed in 2014
-local groups of groundwater sustainability agencies (GSA’s), which each have to form their own groundwater sustainability plan (GSP) with oversight from the state
-the eventual goal is to replace as much water into the groundwater system as we pull out from wells
What is the impact on SGMA on Ag?
-SGMA is absolutely necessary for the sustainability of Ag and people in California
-however, it doesn’t come without cost. We have been over using water for a long time and now we have to pay for it
-it is estimated that by 2040, farm acreage in California will decrease by 20-30% or 900,000
What is the primary issue with urban watersheds?
-Urban areas have high % of compacted soils and land covered with impermeable surfaces ex: rooftops, paved streets, parking lots
-funnel lots of water to small sewage drains and storm drains, increasing erosion
What can be done to increase urban runoff?
-replace solid concrete with permeable pavers or gravel when possible
-replace storm drains going to sewers with “rain gardens”–water is funneled into a landscape