Measure to Manage
Nutrients and Water
Karen Lowell
Agronomist, USDA/NRCS
California Certified Crop Advisor
Karen.Lowell@ca.usda.gov 831.424.1036 x119
Dan Johnson
Water Management Engineer, USDA/NRCS
Dan.Johnson@ca.usda.gov 530-792-5625
Road Map For Our Session Today
• Measure to Manage Concept
• Nutrient Budget
– Preparing a Nutrient Budget: Inputs
– Predicting Plant Available Nutrients
– Resources for Estimating Crop Needs
• Water Budget
– How and Why of Soil Water Monitoring
– Measurement Options
Why Measure to Manage?
• Plan management
• Evaluate outcomes
• Optimize crop yield and quality
• Avoid problems
Basics of Measure to Manage
• Quantifiable Information
• Capacity to Measure
• Knowledge in Context
Key Elements
for Nutrient Management
• Management by The 4 R’s
• Irrigation Water Management
• Nutrient Budget
Nutrient Budget Worksheet
Fundamentals of Nutrient Budget
What are the inputs?
What’s available?
What is the crop need?
What are the Inputs?
Measure to Manage
SOIL
COMPOST
WATER
lbs/acre foot of
water
Nitrogen (as N)
62
lbs of Nutrient/Ton Dry Weight Basis
What is available?
• What is available - predicting biological
and chemical processes
•N from Soil Organic Matter (SOM)
•N from Irrigation Water
•N, P and K from Compost
•N from Cover Crops
What Does The Crop Need?
You have this as a handout. If you didn’t receive
it, send me an email and I will send it to you.
karen.lowell@ca.usda.gov
Irrigation Water Management
•
•
•
•
Track your soil moisture content
Know what your soil will hold
Know your crop soil "dryness" limits
Add water while doing your best to
keep it between the lines
Making every drop count means
counting every drop
Know What Your Soil Can Hold
Two Key Points:
• There are
optimum levels
of water in the
soil.
• The soil can only
hold so much
water.
Soil Moisture Content vs. Time
Root Zone
Moisture
Content
Field Capacity
Allowable dryness
2
1
0
Dry
June 14
June 21
Date
June 28
Irrigation
Wet
You decide how long to
run the system
Practical use – Looking ahead
Practical use – Looking back
Monitoring Soil Moisture
Karen Lowell
Agronomist, USDA/NRCS
California Certified Crop Advisor
Karen.Lowell@ca.usda.gov
831.424.1036 x119
Monitoring
Soil Moisture
Soil Moisture by
Feel and
Appearance
Monitoring
Soil Moisture Climate-Based Method
• Calculates inches of crop
water use
• Sensors collect climatic
data
• Equation (model)
processes data to
calculate “reference” ET
(or ETo)
Wind
speed
Solar
radiation
• Estimated crop ET (ETc) is
the product of ETo X the Computer
current crop coefficient
(Kc)
• Kc will vary by crop and
stage of growth
Humidity
and
Temp
Monitoring
Soil Moisture
Soil Water Tension
(Tensiometers)
Monitoring
Soil Moisture Electrical Resistance
“Gypsum blocks” “Watermarks”
• Display data in centibars
of suction
• Have a wider operating
range (0-200 cb) than
tensiometers
• Requires careful
installation
• Relatively popular
Monitoring
Soil Moisture Capacitance sensors
• One “probe” typically
has sensors at multiple
depths
• Becoming more popular
• Requires very careful
installation
• Readings in % moisture