Soil Testing in Tomatoes Jim Rideout Extension Specialist Soil Fertility

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

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 weeks

New codes Will reduce lime recommendation to account for un-reacted lime

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

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

---------- ---------- +K +K Ca ++ K+ K+ +K +K Ca ++ Ca ++ ++ Mg K+ K+ Ca ++ ++ Mg +H +H Ca ++

Questions?