Agronomic Services - Soil Testing FAQ's

1. Do not ship plant, waste, solution, media/potting soil, or nematode samples in the same box as soil samples.
2. Each established client—grower or consultant—has a PALS ID, which is the customer's account # for the online lab report portal. Including your PALS # on the submission form greatly reduces the chances of billing errors, duplicate accounts, and missing reports. If you don't know your PALS ID, log in to the online portal. Your PALS # is in the top right corner.
3. Label each soil sample box clearly, especially when using Farm IDs. Preprinted, waterproof labels work well for the client’s name.
4. Organize soil samples within shippers. Each shipper holds 36 soil boxes (4 rows of 9 soil boxes). It is helpful to indicate which sample is the first and which is the last in relation to the information sheet. If a shipper contains samples from two farm IDs, note this along with the first and last labels.  Arrange soil sample boxes starting in one corner and filling rows left to right. Use packing paper if the shipper is not full to prevent damage to soil sample boxes.
5. Ensure a printed submission form is included with samples. Samples cannot be processed without this form. For multiple shippers, the submission form may be placed in just the first one. Write "Forms" on the box and label all boxes (e.g. 2 of 6, 3 of 6). Put forms in a plastic bag if samples are wet.
6. Ensure that each sample has a crop code. 
7. Use online sample submission whenever possible. Although you must still print the submission forms to include with the samples, online submission streamlines our data entry process and reduces errors.

As a general rule, test sandy-textured soils every 2 to 3 years and clay soils every 3 to 4 years. However, if problems occur during the growing season, send in a soil sample for analysis.

You can submit soil samples any time of year, but late summer or early fall is a good time to sample for most crops. Any lime or fertilizer that is applied in the fall will have enough time to dissolve and become available for a spring crop. 

• Fruits and vegetables: Collect soil samples 3 to 6 months before planting. 
• Lawns: Collect samples in late summer (mid-August), particularly for cool-season grasses. 

Samples submitted from mid-April through October are usually analyzed within 1-2 weeks. From mid-October through mid-April, the turnaround time may be several weeks due to the large numbers of samples submitted during this time. 

Note: Soil samples are free of charge from April 1 through late November and are $5 from late November through March 31st. The exact date when the fee begins is posted annually on the Peak Soil Season announcement page.

BS% stands for "base saturation percent." It represents the percent of the CEC that is occupied by base-forming cations, primarily calcium (Ca++), magnesium (Mg++) and potassium (K+).  As the soil pH increases, BS% also increases. On  mineral soils that are properly limed, BS% may range from 70 to 90. On mineral soils that are extremely acid (low pH), BS% typically ranges from 50 to 60.

An extractant is a mixture of various chemical reagents dissolved in water. It removes plant-available nutrients from the soil and dissolves them in a liquid phase. Most extractants can remove phosphorus, potassium, calcium, magnesium, manganese, zinc and copper from a sample. Agronomic Services uses the Mehlich 3 extractant, which was developed by NCDA&CS and NCSU and has been extensively validated for NC soils.

Soil pH indicates how acidic or alkaline a soil is. A pH of 7.0 is neutral; below 7.0, the soil is acidic; above 7.0, the soil is alkaline (or basic). For example, battery acid has a very low pH (<3.0); household ammonia is basic and has a high pH (>10.0). Acidic < pH 7.0 > Basic.  Most crops perform best when soil is slightly acidic; 6.0 6.5.

It is a measurement of the hydrogen ion concentration on a logarithmic scale: pH = -log [H+].  A pH of 6.0 is ten times more acid than a pH of 7.0; a pH of 5.0 is 100 times more acid than a pH of 7.0, and so on. 

Generally not. Moss growth is influenced by other conditions, such as shade, poor drainage, soil compaction, poor fertility (although moss grows quite well on fertile lawns) and very acid soils. Although lime will neutralize soil acidity, the other factors that promote moss growth remain the same. Several chemicals are available for moss control. Follow label recommendations for rate and method of application.

Lime is any substance with the capability of neutralizing soil acidity. Most soils contain appreciable amounts of acidic components (hydrogen H+ and aluminum Al+++) that can be toxic to plants. Indeed, lime is the "anti-acid" for soils.

No soil amendment provides as many benefits as lime. Lime raises soil pH, providing a more favorable environment for microorganisms. Dolomitic lime provides the major portion of calcium and magnesium required for plant growth. Furthermore, plants utilize applied fertilizers more efficiently on soils that are properly limed.

Both kinds of lime have the same acid-neutralizing value when applied at equivalent rates. However, they differ chemically. Calcitic lime contains calcium carbonate only. Dolomitic lime is a mixture of calcium and magnesium carbonates that contains at least six percent magnesium. Most of the lime used for agricultural purposes is dolomitic.

Gypsum, also known as land plaster, is calcium sulfate. It is an economical source of calcium and sulfate but cannot be used as a liming material because it does not have the capability to neutralize soil acidity. In fact, applying gypsum to an acid soil (pH less than 5.5) can have adverse effects on certain crops by displacing soil aluminum, which is toxic to plant roots. Gypsum is frequently applied to crops to provide supplemental calcium. There is no substitute for lime in neutralizing soil acidity.

If plants appear chlorotic after a lime application, low manganese is usually the problem. Applying lime raises the soil pH and reduces the availability of manganese. In such cases, manganese should be applied to the soil. Soils with adequate manganese levels should not show symptoms following lime application. The yield increase attributable to lime should more than pay for applying manganese as well—not to mention the residual benefits to be received in following years.

North Carolina soils become quite acid because the warm, humid climate leaches basic cations from the soil. Acid rainfall can also cause soils to become acidic. The basic cations—calcium (Ca++), potassium (K+) and magnesium (Mg++)—are leached from the soil profile and replaced with acidic components (H+ and Al+++) that are toxic to plant roots. The toxic components are neutralized by lime.

Apply lime only when recommended by a soil test. Some soils need to be limed every 2 to 3 years, others every 3 to 4 years. In general, sandy-textured soils need to be limed more frequently than clays because sandy soils are more subject to pH changes caused by leaching and fertilizer treatments.

Ideally, lime should be applied and mixed into the soil before a crop is planted. However, if the need is great, lime can be applied even when plants are already in place. Unlike fertilizers, lime can be spread over growing crops without damaging the crop. When lime has been applied as recommended, do not apply more without taking another soil test.

Soil pH and micronutrient availability are interrelated. Too much lime can raise soil pH to a point where micronutrients become unavailable to plants. Micronutrients affected by pH include iron (Fe), manganese (Mn), zinc (Zn) and, to a lesser extent, copper (Cu). Problems caused by applying too much lime are more difficult to correct than those that result from having applied too little. You can always apply more lime, but you cannot remove it if you put out too much.

When used as specified on the label, pelletized lime is just as effective as powdered lime. Pelletized lime contains finely ground dolomitic lime bound in pellet form. In contact with water, the pellets disintegrate and release the enclosed lime. Pelletized lime is more expensive but easier and less messy to apply than powdered lime. To many homeowners, it is well worth the extra cost.

Lime is only slightly soluble in water and does not move into the soil as effectively as soluble fertilizers, such as nitrogen (N) and potassium (K). Lime reacts with soil acids most effectively when it is mixed with the soil and adequate water is present. However, when lime cannot be incorporated into the soil, a surface application is better than none at all.

Yes. However, surface-applied lime reacts much slower than lime mixed into the soil. Most of the reaction of surface-applied lime occurs in the top 1 to 2 inches of the soil. If you surface-apply lime to established plants, apply no more than 50 lb per 1000 ft² initially, even if your soil test report recommends more. Apply the remainder after six months. On no-till fields, apply only 1.0 to 1.5 tons per acre; apply the remainder within the following year.

With adequate soil moisture, lime begins to react immediately, and pH changes should be evident within a couple of months. However, it takes about 6 to 12 months for the total benefit of lime to be realized. As soil pH increases, the reaction rate of lime decreases due to a lower concentration of soil acids: e.g., the lime reaction rate is higher at pH 5.0 than at pH 6.0.

Clay soils are aluminosilicates and contain more potential acidity than sandy soils. As the pH falls below 5.5, aluminum become soluble at levels toxic to plants. In addition, soluble aluminum reacts with water to produce hydrogen ions, further reducing soil pH. Since clay soils generate more acidity than sandy soils, they require more lime to counteract it.

Soil test measurements of pH and exchangeable acidity indicate whether enough lime has been applied. The purpose of applying lime is to reduce exchangeable aluminum (acidity) to levels that are not toxic to plants. Research shows that nontoxic levels occur at pH values above 5.5. A soil pH of 6.0 is usually recommended to allow for variation in lime application, soil type, climate, fertilizer effects and crop tolerance. Some crops have a higher target pH of 6.0 to 6.5.

Most pH meters and indicator strips sold in hardware and garden centers are not very reliable for measuring soil pH. Accurate pH meters are available but are quite expensive for homeowner use. Consistently reliable results are obtained by submitting samples to a soil testing laboratory.

Chemically, clay and organic soils have many negative sites that attract and hold positively charged nutrient ions, such as potassium (K+), calcium (Ca++) and magnesium (Mg++). Pure sand alone, on the other hand, has no negative sites. The nutrient-holding capacity of a sandy soil is directly related to the amount of clay and organic matter mixed with and coating the sand. In addition, because sandy soils are porous, water moves freely through the soil profile carrying nutrients downward with it.

In a home garden setting, the best way to increase a soil's nutrient-holding capacity is to mix organic matter, such as composted leaves, into the soil. As added benefits, organic matter enhances biological activity within the soil, increases water retention and provides essential plant nutrients. In a field crop situation, green manure (cover crops) can be incorporated into sandy soils to increase nutrient and water retention. To maintain beneficial effects, organic matter must be added to the soil regularly.

CEC stands for "cation exchange capacity." It is a relative measure of the soil's capacity to hold positively charged nutrients, such as potassium (K+), calcium (Ca++), and magnesium (Mg++).  As this value increases, the nutrient-holding capacity of a soil increases. The CEC of soil types from lowest to highest are: sand, sandy loam, sandy clay loam, clay loam, clay, and organic, meaning that sandy soils have the lowest and organic soils have the highest nurient-holding capacity.