Soil Testing in Tomatoes

Jim RideoutExtension Specialist

Soil Fertility

Maintain growth while applying only those nutrients which can not be supplied by the soil in adequate amounts

The Main Idea

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

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

Soil Analysis Basics

NCDA&CS Agronomic Division

Soil Plant tissue Irrigation water Nutrient solutions Nematode assay

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

Recommendation Philosophies

Crop Response Nutrient Replacement (maintenance) Nutrient Buildup Cation Balancing

NC Recommendations – Crop response + some

maintenance

Soil Sampling Methods

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

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

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

Stick With Your Lab Different reporting units Different soil extracting solutions Different yield assumptions Different recommendation

philosophies

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 weeks0

2

4

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10

12

14

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18

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

Nov

Dec

% o

f Y

earl

y S

am

ple

s

Will reduce lime recommendation to account for un-reacted lime

New codes

Interpretation of Results

Now What Do I Do?

Crop Information

Basic Soil Information

Soil pH and Lime

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

Nitrogen

Based on crop code, not on test results

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

Soil Interpretation Indices

I ndex I nterpretation Response

0- 24 Deficient High

25- 49 Low Medium

50- 74 Medium Low

75- 99 High None

100- 124 Excess None

Phosphorus and Potassium

Calcium and Magnesium Expressed as percent of CEC May determine the type of lime

needed Need to consider CEC for gypsum

applications

Calcium and Magnesium

Micronutrients and Sulfur

Salinity Information

Additional Information

Fruit Calcium

Causes of Low Fruit Calcium

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

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

----------

Ca ++

Ca ++

Ca ++

Ca ++

Ca ++

K+ K+

----------

++ Mg++ Mg

+K +K+K +K

+H +H

K+ K+

Questions?