UNDERSTANDING THE SOIL TEST REPORT

Transcription

1 NC STATE UNIVERSITY Urban Horticulture Note No. 6 North Carolina Cooperative Extension Service Durham County Center 721 Foster Street Durham, North Carolina Fax: UNDERSTANDING THE SOIL TEST REPORT The Soil Test Report from the North Carolina Department of Agriculture & Consumer Services (NCDA&CS) is set up for commercial growers, and can seem complex at first glance. For homeowners, the two most important items on the report are the Lime Recommendation and the Fertilizer Recommendation. The soil test report also includes results from approximately 17 lab tests, but home gardeners may find them of little use without an understanding of what they mean. This publication provides a very brief introduction to the complex world of soil chemistry. Sample Report A sample soil test report is shown below. The "Field information" row in gray is the first line of each separate sample analysis. NCDA Agronomic Division 4300 Reedy Creek Road Raleigh, NC (919) Report No: Soil Test Report SERVING N.C. CITIZENS FOR OVER 5O YEARS Durham County Agronomist Comments: B - 4 Field Information Applied Lime Recommendations Sample No. Last Crop Mo Yr T/A Crop or Year Lime N P2.O2s Mg Cu Zn B Mn See Note BED-1 Lawn Crop:Roses lbs Nitrogen or EQUIV per 1000 SQ FT 4 2nd Crop: Test Results Soil Class HM% W/'V CEC BS% Ac ph P-1 K-I Ca% Mg% Mn-I Mn-AI (1) Mn-Al (2) Zn-I Zn-A1 Cu-1 S-I SS-1 NO,-N NH, -N Na MIN ' Field Information Applied time Recommendations Sample No. Last Crop Mo Yr TA Crop or Year Lime N P2.O2s Mg Cu Zn B Mn See Note BED-2 Azaleas 1st Crop: Azaleas l5m (20 lbs or EQUIV per 1000 SQ FT) 4 Test Results Soil Class HM% W/'V CEC BS% Ac ph P-1 K-I Ca% Mg% Mn-I Mn-AI (1) Mn-Al (2) Zn-I Zn-A1 Cu-1 S-I SS-1 NO,-N NH, -N Na MIN Soil ph Fertilizer Recommendation P-Index & K-Index Lime Recommendation Note: The abbreviation "M" means pounds per 1000 Square feet of area, e.g. 45M = 45lb per 1000 ft 2.

2 LIME RECOMMENDATION The Lime Recommendation is given in pounds per 1000 square feet of area. (abbreviated "M"). The recommended lime application should raise the soil ph to the optimum level for the crop you specified, and keep the ph within the desired range for 3 to 4 years on our clay soils. Lime can be tilled into new beds and lawn areas, or broadcast over the surface of established plantings. Irrigation or rainfall will help the lime disperse and will wash away any surface dust. Lime can be applied at any time of year. Lime takes months to fully react in the soil, so apply the recommended amount as soon as possible after you get the Soil Test Report. It's best to apply lime well in advance of planting. Do not surface-apply more than 50 lbs of lime per 1000 ft² at any given time. If the suggested rate is higher, apply 50 lbs initially and the remainder after six months. Retest six months after the second application to make sure the soil ph is in the desired range. FERTILIZER RECOMMENDATION The Fertilizer Recommendation is given in pounds per 1000 square feet of area. The recommended fertilizer will provide enough phosphate and potash (P and K) for an entire growing season. The recommended fertilizer will also provide a baseline amount of Nitrogen, 1 lb N per 1000 ft, but many plants need more N than this baseline amount. Your Durham County Extension Center can provide detailed information on fertilizer needs for specific plants. You must adjust the fertilizer recommendation to the size of your bed or lawn area. You may need to use an alternative to the recommended fertilizer formulation. The NCDA&CS makes fertilizer recommendations based on formulations that are commonly available through farm supply houses - not the ones most common in home & garden centers! Examples are given below. Timing of fertilizer application is important. Applying fertilizer at the wrong time of year may be harmful to plants, and can also contribute to nutrient pollution of streams and groundwater. Consult your Durham County Extension Center for the correct times to fertilize. TEST RESULTS The last two lines of information for each sample are the Test Results. The meanings of the abbreviations are described in Table 1 below. Most of these analyses need not concern the home gardener, but a few will help you understand your soil and your soil test recommendations better. Soil ph is a measure of how acidic or alkaline the soil is. The scale goes from 1 (acidic) to 14 (alkaline), with neutral being 7.0. Most lawns, vegetables and landscape plants prefer a soil ph around 5.8 to 6.5. Plants cannot take up soil nutrients if the soil is outside their preferred ph range. Our soil is naturally quite acid, often with a ph below 5.0. Several nutrients (including Phosphorus and Potassium) are reported on an "index" scale of 0 (low) to 100+ (high). This indexing makes the results easier to interpret.

3 When the Phosphorus Index (P-I) and/or Potassium Index (K-I) are below 10, adding the missing nutrients) can dramatically improve plant growth. A level of 50 or over is adequate; above this level, there is little plant response from adding more of the nutrient. Phosphorus and Potassium are both important for good root growth. Phosphorus is essential for good flowering and fruiting. Nitrogen is only tested if the grower specifically requests it; the results are not very reliable. Nitrogen levels in the soil depend on many factors, including rainfall, crop growth, microbial activity, and the amount of organic material in the soil. The nitrogen fertilizer recommendation is a general one, based on average crop requirements. Table 1: Test Results Headings Soil Class: MIN = Mineral, M-O = Mineral-Organic, ORG = Organic HM % = percent humic matter, a measure of how much decayed organic matter is in the soil VV';'V' = weight per volume, a measure of how dense the soil is CEC = cation exchange capacity BSI/. = percent of CEC occupied by bases (ions with a negative charge) Ac = soil acidity (decreases as ph increases) ph = ph: below 7.0 is acid; exactly 7.0 is neutral; above 7.0 is alkaline. P-I = phosphorus index K-I = potassium index Ca% = Calcium percent Mg% = Magnesium percent Mn-l = Manganese index; Mn-Al =manganese availability index Zn-I = Zinc index; Zn-AI = Zinc availability index Cu-I = Copper index S-I = Sulfur index SS-I = soluble salt index (not routinely tested) NO3-U = nitrate nitrogen (parts per million, or ppm) (not routinely tested) NH4N = ammonium nitrogen (parts per million, or ppm) (not routinely tested) Na = Sodium FERTILIZER FUNDAMENTALS For more in-depth information on fertilizer, see Durham County Extension Urban Horticulture Note 4: Improving Soil Fertility. Fertilizers are labeled with a three-letter code that gives percentages of three major nutrients: Nitrogen (N), Phosphate (P), and Potash (K). The numbers are always in this order. Fertilizer recommendations on the soil test report are given in pounds per 1000ft². In the examples below, this is abbreviated "M", e.g. 2M = 2 lb per 1000 ft². The recommended fertilizer will provide enough P and K for an entire growing season. Many landscape and vegetable plants need more N than the soil test report suggests. The formula for calculating how much fertilizer to apply, given a nutrient recommendation and the fertilizer's N-P-K formulation, is given at the end of this publication.

4 Dangers of Over-Applying Fertilizer Fertilizers are soluble salts, and may leach into groundwater or wash out of the soil with heavy rains. Nutrients from fertilizers, particularly nitrogen, are a significant source of water pollution. Residential landscape care contributes as much to nutrient pollution as farming. If over-applied, the salts in fertilizers can burn plant roots and damage foliage. This is true for both synthetic and organic fertilizers. Several light applications are usually preferable to one heavy application. Slow-Release Fertilizers Both synthetic slow-release fertilizers and organic fertilizers break down slowly in the soil, releasing their nutrients steadily over the growing season. These fertilizers are less likely to contribute to nutrient runoff. They are also less likely to cause fertilizer injury. An added benefit to the gardener is that it can be applied once for the whole season. Whenever possible, choose a slow-release fertilizer. Organic Fertilizers Organic fertilizers tend to be lower in nutrients (per weight) than synthetic fertilizers. They may be more expensive than synthetics. They are bulky to handle and are sometimes smelly. They compensate for these shortcomings by contributing organic material to the soil. Decomposed organic material in the soil lightens soil texture, discourages compaction, improves drainage and aeration, adds nutrients, moderates soil temperature, and provides pore space, which is essential to plant growth. 10 lb of has the same nutrients as 200 lb of bagged composted cow manure ( ). However, the composted manure contains a great deal of useful organic matter. If a new bed is being prepared, the bulkier cow manure would be a better choice for improving the soil than a sprinkling of Nitrogen Only Alternative Fertilizer Formulations If your report recommends "1 lb Nitrogen or equivalent," then your soil has adequate P and K for food plant growth (P-I and K-I numbers above 50i, and only N must be supplied. Examples of N-only fertilizer are ammonium nitrate (34-0-0) and dried blood (12-0-0). Be careful not to over-apply nitrogen fertilizers. Why? see Dangers of Over-Applying Fertilizers, above. Alternative #1: You may choose to use a lawn fertilizer, which is typically high in nitrogen (around 30,0) and relatively low in other nutrients. Often some of the nitrogen is in a slowrelease form. Alternative #2: You also have the option of using or a similar balanced fertilizer. This will give you more P and K than you need, but in most soils, this is not a problem. If Your P-I and K-l numbers are above 75, consider one of the other alternatives.

5 Table 2: Nitrogen-Only Fertilizers N P K Recommendation: 1 lb N or equivalent per 1000 ft² 1 N only fertilizer 3.33M of or 8.3M of dried blood (12-0-0) 1 Alternative # M of lawn fertilizer such as Alternative #2: 10M of Alternative Fertilizer Formulations A typical recommendation is 7M or 1 _ This recommendation provides the baseline amount of N, plus extra K, suggesting that the P-I number on your report is over D0 and the K-I is under 50. Alternative #3: One alternative is to apply a combination of an N-only fertilizer plus Muriate of Potash (0-0-60; for additional K. See above for examples of N-only fertilizers. Alternative #4: Again, you have the option of using or a similar balanced fertilizer. This will give you more P than you need. If your P-I is over 75, use Alternative #4. Since is not as concentrated as , you will need to use more Table 3: Alternatives for N P K Recommendation: 7 lb per 1000 ft² 1 1 Alternative #3: 1 M N from Nitrogen-only fertilizer plus 1.67M of Alternative #4: 10M of or Alternative Fertilizer Formulations A typical recommendation is 20M of This recommendation provides the baseline amount of N, plus extra P and K, suggesting that the P-I and K-I numbers on your report are both under 50. A similar recommendation is for 20M of 5-10-J. In this case, the K-I number is probably over 50.

6 Alternative #5: Flowerbeds often need more than the recommended amount of N for the growing season. A good alternative for this type of garden is to use a balanced fertilizer that will supply the extra P and K, plus additional N. If your K-1 is over 75, use Alternative #2. One option is to apply a balanced slow-release fertilizer (such as Osmocote ) at a rate that will give you the recommended amounts of P and K. Your plants will take up the extra N as it is released over the season. Alternative #5a: You may also use a non-slow-release balanced fertilizer (such as ). Apply half the recommended amount early in the spring and the other half about six weeks later. Whv? see Dangers of Over-Applying Fertilizers, above. Alternative #6: Trees and shrubs don't need any more N than is recommended in the report. Apply a balanced fertilizer to get the right amount of N. Add Triple-Super phosphate (0-60-0) for additional P. If needed, add Muriate of Potash (,0-0-45) for additional K. Table 4: Alternatives for and N P K Recommendation: 20 M of per 1000 ft² or 20 M of per 1000 ft² 1 2 Alternative #5: 14.3 M of slow-release Alternative #5a: 2 applications, each 10M, of or 1 Alternative #6: 10M of plus 2.25 M of plus (if needed) 1.67M of Other Formulations Alternative Fertilizer Formulations Some manufacturers offer balanced fertilizers with different levels of nutrients. Use these just like , but use less or more to compensate for differences in concentration. The formula for calculating how much fertilizer to apply is given below. Here is a handy conversion: 10 lb of = 12.5 lb of = 7.14 lb of lb of has the same nutrients as 200 lb of bagged composted cow manure ( ).

7 CALCULATING HOW MUCH FERTILIZER TO APPLY In English: in math: Further explanation: The number of pounds of the nutrient 1 M 1 lb N per 1000 ft 2 you want to apply (per unit area) of N ~ I using fertilizer divided by the percentage of that = 0.10 = 10% w in fertilizer nutrient in the fertilizer analysis gives the pounds of fertilizer to = 10 M = 10lIb of per 1000 ft' apply (per that same unit area) I fertilizer FOR MORE INFORMATION Master Gardener Volunteers at the Durham County Extension Center can provide advice and helpful publications on many gardening and landscape topics. We can also help you interpret your soil test report. Master Gardener Volunteers are in the office daily our phone number is We welcome your calls! The following are a few of the publications available from your Durham County Extension Center: Urban Horticulture Note 1: Durham's Weather Urban Horticulture Note 2: Durham's Soil Urban Horticulture Note 3: Amending Clay Soils Urban Horticulture Note 4: Improving Soil Fertility Urban Horticulture Note 5: Submitting Samples for Soil Testing Urban Horticulture Note 6: Understanding the Soil Test Report Urban Horticulture Note 7: Planting Trees & Shrubs Publication AG-69: Carolina Lawns Publication AG-46 7: Composting: Managing Yard Wastes Publication WQWM-151: Home Lawn Care and Water Quality Leaflet No. 551: Bedding Plants: Soil Preparation & Fertilization Prepared by the Durham County Master Gardener Volunteer Program Revised October 2007 The use or brand names in this publication does not imply endorsement of the products or services named or criticism of similar ones not mentioned.