How Do You Know How Much Nitrogen in My Soil From Soil Testing
Fertilizing plants without knowing the soil pH and fertility is like planning a trip without knowing the starting point. You have to know where y'all are to know what steps to take to become to your destination. You must know the existing pH and fertility to decide how much (if whatsoever) lime and fertilizer to utilize for optimum institute growth.
Why Test the Soil?
Soil testing is a quick and accurate method to determine the relative acidity of the soil (pH) and the level of several essential nutrients (phosphorus, potassium, calcium, magnesium, sodium, sulfur, manganese, copper, and zinc) needed. The test results will assist y'all in plant selection, soil preparation, and fertilization. They volition aid y'all avoid overfertilization, which can stimulate excessive plant growth and increase the likelihood of some diseases. Information technology can too assistance reduce pollution of our water supplies. Backlog nutrients applied, only not used by plants, may run off into surface waters during storms or leach into groundwater. By applying the right class and corporeality of fertilizer, you volition avoid unnecessary pruning of excessive new growth and have healthier, more productive plants.
A soil test is the only reliable method to determine soil pH. Most soils in Northward Carolina are acidic, and some are as acidic as vinegar. Soil pH is a measure of the hydrogen (acid-forming) ion activity of the soil solution. The pH calibration of measuring acidity or alkalinity contains 14 divisions known as pH units. It is centered at pH 7, which is "neutral." The lower the number, the more acidic the soil. The higher the number, the more alkaline. The pH scale is non a linear scale merely a logarithmic scale. A soil with a pH of 4.0 is 10 times more than acidic than soil with a pH of 5.0 and is 100 times more than acidic than soil with a pH of 6.0.
Soil pH is influenced by parent material (rock that soil is formed from), precipitation, native vegetation, crops grown, soil depth, and the type and amount of fertilizer used. As organic matter decomposes, acids are produced that exit the soil more than acidic. Also, equally water from rainfall or irrigation passes through the soil, acids displace bones cations (positively charged ions) such as calcium (Ca) and magnesium (Mg), which are then leached from the soil. Acidity more often than not increases (pH decreases) with soil depth, then soils that are eroded are acidic unless properly limed. Heavy utilize of some nitrogen fertilizers also can increase soil acerbity.
Soil pH affects the availability of nutrients in the soil too as those applied equally fertilizer (Figure ane). Low pH can cause some elements to become chemically bound to soil particles, which makes them unavailable to plants. Microorganisms responsible for the decay of organic matter may be limited or inactive in highly acidic soil. The ability of legumes to prepare nitrogen is also reduced. But when the pH rises above six.5, trace elements such equally fe, manganese, copper, and zinc become less available. The availability of most nutrients is greatest at pH half dozen.v.
Plants require different pH levels for optimum growth and productivity. A slightly acidic soil (pH 6.0 to 6.five) by and large is considered ideal for most plants in Due north Carolina. Nonetheless, blueberries, rhododendrons, mountain laurel, and centipedegrass grow best in soils with a pH between v.0 and 5.5. If the soil pH is to a higher place the preferred range for a plant, growth volition be slowed or the plant may develop stress bug, such as diseases, insects, nutrient deficiency symptoms, and dieback.
Factors Affecting Soil pH
Soil pH is influenced by parent material (stone that soil is formed from), precipitation, native vegetation, crops grown, soil depth, and the blazon and amount of fertilizer used. Every bit organic thing decomposes, acids are produced that leave the soil more than acidic. Also, as water from rainfall or irrigation passes through the soil, acids displace basic cations (positively charged ions) such as calcium (Ca) and magnesium (Mg), which are then leached from the soil. Acerbity generally increases (pH decreases) with soil depth, so soils that are eroded are acidic unless properly limed. Heavy use of some nitrogen fertilizers also can increase soil acerbity.
Figure 1. Nutrient availability as affected by soil pH. The wider areas represent greater availability.
How To Test Soil
About inexpensive, commercially available soil test kits are not reliable. Even if they accurately measure pH, they practise not signal the amount of lime needed. Soil texture, organic matter content, crop to be grown, target pH, soil acidity level, cation exchange capacity (CEC), type and amount of dirt, and current pH are factors to consider in determining the amount of lime needed to raise the soil pH.
Consistently reliable results can only be obtained by submitting samples to a soil-testing laboratory. The North Carolina Department of Agriculture and Consumer Services Agronomic Division will analyze your soil samples gratis of charge or for a pocket-size fee. Forms and boxes for samples are available from your local county Cooperative Extension center.
When and how often should soil be tested?
Soils samples may be taken any time of the twelvemonth. The pH and phosphorus level are relatively constant throughout the year unless lime, fertilizer, or organic matter has been applied recently. It's best not to sample immediately after applying lime, fertilizer, compost, or manure.
The soil-test written report will make recommendations for the next growing flavour, and so test soil several months earlier planting or fertilizing. For a cool season lawn, submit samples the previous summer; for a warm-flavour lawn, submit samples in the fall or winter. For a spring vegetable garden or flower bed, submit a sample in the fall or winter.
If the soil-test written report indicates the pH and nutrient levels are in the range needed for plants to exist grown, you may not demand to sample every twelvemonth. If the levels are excessively loftier or low, you should submit a sample every twelvemonth to make up one's mind how much improvement has been achieved and what additional amendments should exist made. Equally a general rule, test sandy soils every 2 to 3 years and clayey soils every three to 4 years.
How to have a soil sample
The accuracy of the soil-test report depends on the quality of the soil sample. It is all-time to collect soil samples with stainless steel or chrome-plated tools. The all-time tool to use is a soil coring tool. It takes an equal corporeality of soil from the surface through the sampling depth and an equal corporeality from each site. A shovel or trowel can exist used if a coring tool is not available. Avert using brass, statuary, or galvanized tools, which may contaminate the sample with copper and/or zinc. Put the sample in a clean, plastic bucket; even minor amounts of residual lime or fertilizer will affect test results (Figure 2).
Scrape leaves, mulch, and other debris from the soil surface. When using a trowel or shovel, dig a hole to the appropriate depth for each blazon of plant to be grown, then scrape soil from the side of the pigsty—one stroke, bottom to height. For gardens, new lawns, and other cultivated areas, sample to the depth the soil has been or will be tilled. For established lawns, collect samples 4 inches deep. For vegetable gardens and flower beds, take samples vi to viii inches deep, and for trees and shrubs, sample to a depth of 6 to 10 inches.
Repeat this procedure in six to 8 areas (subsamples) and combine to obtain a more than representative sample for testing.
Avert areas that are evidently different—wet spots, the compost pile, animal urine spots, castor piles, under eaves, and sites where trash has been burned. Mix the subsamples together to obtain 1 composite sample. Remove big pieces of organic textile such equally roots, stalks, leaves, rocks, and other droppings. Fill the soil sample box to the fill up line. Submitting less than the suggested amount of soil could lead to a sample that does not adequately correspond the area you are testing or may not produce enough soil to conduct all of the necessary tests .
Even if the soil looks the same, have separate samples for each general type of institute to be grown-flower beds, vegetable gardens, fruit orchards, shrub borders, and lawn areas. It'due south not necessary to list each plant to be grown. But if only one blazon of institute is to be grown, be specific; for instance, list fescue for lawns and apples instead of fruit trees. You will receive a report for each expanse. Areas with different soil types should exist sampled separately. Soils vary past location, gradient, the corporeality of fertilizer applied in recent years, and in their concrete, chemical, and biological properties. Soil variations tin can also result on a new home site when soil is moved around or brought in to fill up low areas.
Soil wet will not bear on soil-test results directly. All the same, information technology's best if the soil is slightly damp to dry-not moisture when samples are collected. If the soil is too wet to till, it's too wet to sample. Wet soil is more difficult to mix and could damage the soil sample box during shipment.
Problem Expanse Samples
If yous take plants in ane area that are not doing well, submit a problem area soil sample. Take ane soil sample from the problem expanse and another from a skilful area for comparison. Fill out the Diagnostic Soil Sample Information Canvas (Course AD2) instead of the regular soil sample canvas.
Completing the soil report form
Enter your name, address, and a five-digit lawmaking that y'all make up on the side of the box using a ballpoint pen, permanent marker, or a No. 2 pencil. Felt tip pens or hard pencils may be difficult to read at the soil-testing lab-especially if the soil box gets wet. Make upwards a code that will be piece of cake to remember—"lawns" for lawn, "veggie" for vegetable garden. Any combination of letters and numbers may be used. Fill out the soil-test report sheet, giving every bit much information as possible. The required items are name, address, county, crop code (found on the back of the sail), and the crop (plants) to be grown. The course is too used by farmers, and then some of the data requested, such every bit pounds of lime per acre, may not seem to apply to gardeners.
Fold the report grade and so information technology tin can exist inserted between the flaps in the top of the sample box or record information technology to the sample box. Do not put the information sheet inside the sample box.
At that place is no need to record the bottom of the box to preclude soil from sifting out. If more than one sample is to be sent, identify all samples in a paper bag or cardboard box. Placing soil or boxes in a plastic bag will prevent the soil from air-drying and will take longer to analyze. M ail your sample to the NCDA&CS lab at 5300 Reedy Creek Road in Raleigh.
Figure two. Use a coring tool or trowel to collect soil samples and place them into a clean bucket before transferring them to a soil sample box.
Karen Neill
Soil Test Results
Subsequently the soil-testing lab receives your sample, it dries the soil and conducts tests to decide the soil pH, humic matter content (the chemically active portion of organic matter), nutrient content, and substitution capacity (ability to hold nutrients). The lab chemically removes elements from the soil and measures them for their constitute availability. The quantity of available nutrients in the sample, except for nitrogen, is used to make up one's mind the corporeality of fertilizer that volition be recommended.
Test results and suggested lime and fertilizer application rates will be posted on the Agronomic Services Division'due south Public Access Laboratory-information-management Organization (PALS). The turnaround time is almost ii weeks during the summer and several months in tardily autumn or early winter.
The study has two sections-examination results and lime and fertilizer recommendations. The exam results section includes measurements of pH, phosphorous (P), and potassium (K). The Recommendations sections will provide guidance for applications of lime as well as N-P-1000 fertilizer.
Agreement soil-examination written report terms
Soil class : Each soil sample is classified according to humic matter content. The classes are:
MIN: Mineral soil. Low percentage of humic matter. Target pH half-dozen.0.
M-O: Mineral-organic soil. Medium percentage of humic matter. Target pH 5.5.
ORG: Organic soil. High humic affair content. Target pH 5.0.
Target pH is the soil pH that is best for most plants. Mineral soils need to be limed to a college pH than the two other types of soil to reduce aluminum (Al) to levels that will allow optimum growth. Mineral-organic and organic soils are higher in organic matter and lower in aluminum.
HM percentage : Humic matter percent is a measure out of the chemically active fraction of organic matter. The humic matter values are usually much lower than the actual organic affair content.
Due west/V : The soil weight/book is shown in grams/cubic centimeter and is used to determine the soil grade. Soils loftier in sand accept high Westward/V, while soils high in organic matter have low W/V. Loamy and clayey soils are intermediate.
CEC : Cation exchange chapters is a measure of the soil's capacity to concord basic cations such as potassium, calcium, and magnesium, plus the acidic cations hydrogen and aluminum. CEC increases as soil organic matter, pH, and clay content increase. This calculation is given in milliequivalents per 100 grams of soil. Cations are positively charged ions such every bit calcium (Ca++), magnesium (Mg++), and potassium (Chiliad+). The larger the CEC value, the more cations the soil is able to hold against leaching.
BS% : Base saturation per centum is the percent of the CEC that is occupied by the bones cations [potassium (K), calcium (Ca), and magnesium (Mg)]. BS% indicates the pH and lime condition of the soil. Every bit pH increases, BS% besides increases. On soils that are properly limed, BS% should range from 70 to 90. On acidic soils, BS% ranges from l to 60.
Air-conditioning : Exchangeable acidity is the portion of the CEC that is occupied by acidic cations [Aluminum (Al), hydrogen (H)]. The amount of acidity decreases as soil pH increases.
pH : Soil pH is a measure of the active acidity [hydrogen (H)] in the soil solution.
P-1 and Thousand-ane : Phosphorus (P) and potassium (K) are shown as indexes used to evaluate nutrient availability to plants. Fertilizer recommendations for P and K decrease equally the index increases. An index of 25 or lower is considered besides depression for optimum establish growth. A range of 26 to 50 is medium, and an index of greater than l is high. Adding more phosphorus when the index is greater than l should not generate a response. Fertilizer rates are given as pounds of PtwoO5 and Yard20 per acre or per 1,000 square feet.
Ca and Mg% : Both calcium (Ca) and magnesium (Mg) are shown equally percentages of CEC. Soil calcium is seldom low enough to limit plant growth. In full general, calcium is the most common cation in the soil. Calcium percentage is essential for calculating CEC and to evaluate the relationship between calcium, magnesium, and potash (K). If the magnesium percentage is low, magnesium will exist recommended in the form of dolomitic lime or of a fertilizer containing magnesium.
S (sulfur), Mn (manganese), Zn (zinc), Cu (copper) : An alphabetize is determined for each of these nutrients. An index of 25 or lower is considered too low for optimum constitute growth. A range of 26 to 50 is medium, and a range of greater than 50 is high. Adding more than nutrients should not generate a response when the index is greater than 50. Sulfur is difficult to interpret since, like nitrogen, it leaches readily from sandy soils.
SS-1 : The soluble salt index is a measure of the amount of fertilizer elements and sodium that are soluble in the soil. This test is unremarkably done for greenhouse production and problem area soil samples. A moderate level of soluble salts is desirable, but an excessive amount can injure plants. The degree of injury from soluble salts depends on the soil blazon, soil moisture, and crop sensitivity.
Na : Sodium is reported as meq/ dm3. Sodium can harm constitute growth when information technology exceeds xv percent of the CEC. You can leach excessive sodium from the soil by applying gypsum (land plaster).
N (nitrogen) is not routinely a part of the soil-examination regimen considering the test has express predictive value. Nitrogen is quite mobile in the soil and may be leached out before planting.
Recommendations for its utilize are based on the amount of nitrogen unremarkably needed for establish growth in a year.
Lime and fertilizer recommendations
When the soil pH is in the ideal range for optimum plant growth, no lime recommendation is given. If the pH was adamant to be too low, a recommendation is made to apply lime at a given charge per unit per M. The M stands for ane,000 square feet. Occasionally, the recommendation is given in tons per acre. An acre is 43,560 square feet, and a ton of lime weighs ii,000 pounds. One ton per acre equals 46 pounds per i,000 square feet.
Sometimes soils with an identical pH will have unlike lime recommendations. Soils low in organic thing or high in sand require less lime to change the pH than clayey soils or those with loftier organic affair. Clayey soils incorporate more potential acidity than sandy soils. Equally the pH falls beneath 5.5, aluminum becomes soluble at levels toxic to plants. In addition, soluble aluminum reacts with h2o to produce hydrogen ions, further reducing soil pH. The purpose of liming is to reduce exchangeable aluminum to levels that are not toxic to plants.
Calculating the Amount of Lime and Fertilizer to Apply
A one,000-square-feet area is an expanse 50 feet by xx anxiety. Multiply the length of the surface area by the width of the area to determine the number of square feet. Split by ane,000 to obtain the number of units to be treated. Multiplying the number of units by the pounds of fabric to care for ane,000 square feet will requite y'all the amount of fertilizer and lime needed.
Case:
If the expanse is 500 feet by 20 feet, and the suggested lime or fertilizer handling is 30M (pounds per one,000 square feet):
500 feet × 20 feet = x,000 square feet
Split 10,000 square feet by i,000 = x units
Multiply xxx pounds by 10 units = 300 pounds of material (fertilizer or lime)
Liming to raise soil pH
2 full general classes of liming fabric may exist used to raise the soil pH. Calcitic lime is composed of calcium carbonate and can be used on soils high in magnesium. Dolomitic lime is a mixture of calcium and magnesium carbonates; it should be used on soils low in magnesium. Many organic soils and some piedmont soils are naturally high in magnesium, while most sandy soils in the coastal patently are low in magnesium. Dolomitic lime provides the major portion of calcium and magnesium required for found growth. Gypsum, also called land plaster, is calcium sulfate. Information technology is an economic source of calcium and sulfur, but it does non affect soil pH.
All limestone sold in North Carolina must have a label showing the guaranteed percentage of calcium, magnesium, and calcium carbonate equivalent, besides every bit the pounds of material that equal one ton of standard lime.
Lime tin exist purchased in powder or pellet class. The finer the powder, the more speedily it becomes effective. Pelletized lime contains finely basis dolomitic lime spring into pellets. The pellets disintegrate and release the lime when they contact water. It is usually more expensive, but easier and less messy, to employ pelletized lime than powdered lime. The lime will act more than quickly if the soil is retilled several days after the pellets have been mixed into the soil and take had time to soften.
Changing the soil pH
If the soil pH is as well acidic, lime can be used to raise the pH. It can exist applied whatsoever time of the year. Lime raises the pH, providing a more than favorable environment for soil microorganisms. Also, plants utilize fertilizers more effectively at the proper pH. Ideally, lime should exist applied and incorporated into the soil before planting.
If the soil pH is also alkaline metal for the plant to be grown, lower the soil pH by incorporating an acidic soil amendment such every bit pine bawl or peat moss or by applying elemental sulfur. Use sulfur with caution since applying too much can harm plants.
Lime must be mixed with acidic soil and have acceptable water to react with the soil. To exist effective, lime should exist spread and thoroughly incorporated. Lime is just slightly soluble in h2o and does not motility into soil as effectively as soluble fertilizers. With acceptable moisture, lime begins to react immediately; nonetheless, it can take 6 to 12 months to realize the total benefit from lime.
Surface-applied lime reacts more slowly than lime incorporated into the soil. Notwithstanding, a surface application is ameliorate than no application. Most of the surface-applied lime stays in the height ane to 2 inches of soil. For established lawns, gardens, and ornamentals, up to 50 pounds of lime per one,000 foursquare feet tin can be surface applied in one application. For rates over l pounds, look several months to brand a echo application. In lawns, it'south best to aerate the soil before applying lime.
Substituting different grades of fertilizer
The soil-exam written report gives recommendations for a charge per unit and class of fertilizer to use per 1,000 square feet. One class of fertilizer tin be substituted for another, simply you will need to make a few calculations. For example, when the written report recommends 10 pounds of 10-10-10 to apply 1 pound of nitrogen per 1,000 square anxiety but you want to use a 15-15-fifteen fertilizer, use the following formula:
Pounds of nitrogen desired per 1,000 square feet ÷ Percentage of nitrogen in fertilizer you plan to use divided by 100 = one ÷ (xv ÷ 100) = one ÷ .15 = 6
When the soil has a loftier phosphorus index (P-I), the study may recommend an unusual fertilizer class such every bit 15-0-14 or 8-0-24. A fertilizer that contains a small amount of phosphorus (the middle number in the fertilizer analysis) can be substituted for a fertilizer grade that may be next to impossible to detect. When the phosphorus index is below 25, a fertilizer with a high phosphorus content is recommended. An alternative method to apply acceptable phosphorus is to use a high phosphorus fertilizer, such as 0-46-0, and a conventional fertilizer, such as 10-10-10.
Some fertilizer recommendations pertain to nitrogen but, such as 1 pound of bodily nitrogen per 1,000 square anxiety instead of pounds of a complete fertilizer. This blazon of recommendation usually is given when the P and K indexes are over 50. To determine the amount of fertilizer to use when only nitrogen is recommended, divide 100 by the get-go number in a fertilizer analysis (percent nitrogen). For example, if you are using 33-0-0 fertilizer and want to apply 1 pound of actual nitrogen per i,000 square feet, split up 100 by 33 = iii.three pounds of actual fertilizer to apply. Table 1 gives the corporeality of several materials to utilise if merely nitrogen is needed. Unless the soil is deficient in other nutrients, a fertilizer high in nitrogen or containing only nitrogen is often the all-time buy.
| Awarding rates per: | |||||
| 1,000 Square Feet | 100 Square Feet | 10 Foursquare Feet | |||
| Source | Pounds | Cups | Pounds | Cups | Tablespoons |
| 10-10-10 | x | 20 | i | 2 | 4 |
| 8-8-eight | 12.5 | 25 | 1.2 | two.5 | 5 |
| 12-iv-8 | 8 | 16 | .75 | 1.5 | 3 |
| 16-4-8 | half dozen | 12 | .5 | 1 | ii |
| 5-x-10 | twenty | 40 | 2 | 4 | 8 |
| 12-6-6 | 8 | sixteen | .75 | ane.5 | 3 |
Acknowlegment
This publication is a revision of an earlier version. The authors would similar to thank Erv Evans for his earlier contributions.
Contact Luke Gatiboni for additional information.
Publication date: Aug. 20, 2019
AG-614
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Source: https://content.ces.ncsu.edu/a-gardeners-guide-to-soil-testing
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