Soil Testing in Tomatoes

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Soil Testing in Tomatoes

• Jim Rideout
• Extension Specialist
• Soil Fertility

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The Main Idea
Maintain growth while applying only those
nutrients which can not be supplied by the soil
in adequate amounts
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Other Reasons

• Routine monitoring can spot nutrient problems
  before they become nutrient deficiencies
• Mountain soils are extremely variable
• Fertility can be considered part of a good IPM
  program

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How Tomatoes Differ from Agronomic Crops

• May have drip fertigation
• Must manage calcium
• Need to consider source of nutrients
• Earliness and quality are important
• High value per acre

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Soil Analysis Basics
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NCDACS Agronomic Division

• Soil
• Plant tissue
• Irrigation water
• Nutrient solutions
• Nematode assay

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What Does Soil Analysis Measure ?

• The extractable nutrient concentration in a soil
  sample
• Does not measure the total nutrient concentration
• Estimates the ability of the soil to supply
  nutrients to a crop
• Optimized for annual row crops

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Recommendation Philosophies

• Crop Response
• Nutrient Replacement (maintenance)
• Nutrient Buildup
• Cation Balancing
• NC Recommendations
• Crop response some maintenance

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Soil Sampling Methods
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Importance of Collecting a Representative Soil
Sample

• One acre of soil, 6 deep, weighs about 2,000,000
  pounds
• Weight of soil in box about 1 pound
• Weight of sample analyzed is about 2.5 g (1/10)
  of an ounce

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Selecting Areas for Routine Sampling

• Areas should be less than 5 acres
• Similar soil type and crop history
• Similar fertilization history
• Keep blocks same year to year

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Soil Sample Handling

• Mix cores well in clean plastic bucket
• Fill box to line
• Do not oven-dry sample
• Send sample in for analysis as soon as possible

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Stick With Your Lab

• Different reporting units
• Different soil extracting solutions
• Different yield assumptions
• Different recommendation philosophies

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NCDA Sample Volume

• 252,025 soil analyses last year
• Turnaround time varies by month
• 7 to 10 days in summer
• February 2004
• 5 to 6 weeks

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New codes
Will reduce lime recommendation to account for
un-reacted lime
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Interpretation of Results
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Now What Do I Do?
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Crop Information
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Basic Soil Information
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Soil pH and Lime
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Lime Recommendations

• Actual pH
• Acidity (buffer pH)
• Target pH (6.5 for tomato)
• Residual credit for applied lime
• CANNOT make an accurate lime recommendation based
  on pH alone

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Nitrogen
Based on crop code, not on test results
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NCDA Index System

• Unique to North Carolina
• Converts nutrients to common units for
  interpretation
• Used for P, K, Mn, Zn, Cu, S
• Similar to index used for tissue

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Soil Interpretation Indices
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Phosphorus and Potassium
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Calcium and Magnesium

• Expressed as percent of CEC
• May determine the type of lime needed
• Need to consider CEC for gypsum applications

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Calcium and Magnesium
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Micronutrients and Sulfur
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Salinity Information
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Additional Information
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Fruit Calcium
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Causes of Low Fruit Calcium

• Low soil calcium
• Low soil pH
• Nutrient imbalances
• Excessively wet or dry soil
• Large fruit
• Variety differences

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Cation Balance and Fruit Calcium

• Must balance calcium, potassium and magnesium in
  the soil
• Excessive potassium fertilization can reduce
  fruit calcium content
• Excessive magnesium fertilization from dolomitic
  lime can reduce fruit calcium content

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K K
Ca
K K
K K
Ca
Ca
Mg
K K
Ca
Mg
H H
Ca
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Questions?