Laboratory Manual

Experiment 3. Soil Testing

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SOIL TESTING, LIMING, AND FERTILIZING

Many soil scientists feel that fertilizer should be used to remedy plant nutrtient deficiencies of the soil only after a soil test has been made. In most areas one can mail samples of soil to the county or state agricultural extension service office for testing. In some cases, the test is free; in others, it may run $5.00 or more for each individual test. [Presently, at the University of Massachusetts, soils are tested by the Soil and Plant Tissue Testing Laboratory, West Experiment Station Building, for a fee of about $8.00. This test provides pH, lime requirement, nitrate, ammonium, phosphorus, potassium, calcium, magnesium, and some minor and nonessential elements]. Soil testing services have work-loads which vary with the season; consequently, they may be very busy during the spring of the year. Planning should be made accordingly.

A good way to gain an understanding of your soil fertility is to use a portable soil testing kit. Several makes are on the market. Prices range from a dollar or so for acidity test kits to $300 for complete test kits for liming, N, P, K, Ca, Mg, some minor elements, and Al. Test kits for the minor elements are available, but ordinarily one would restrict activities to testing for N, P, K, and lime requirements, leaving tests for minor elements to the professional or extension services.

SOME COMMON SOIL TEST KITS

Name of Kit	Manufacturer
Hellige-Truog	Hellige, Inc., 3718 Northern Blvd., Long Island City, New York.
LaMotte	LaMotte Chemical Products, Co., Chestertown, Md.
Simplex	The Edwards Laboratory, 3606 Venice Road, Sandusky, Ohio
Links to Websites	http://www.agr.state.nc.us/cyber/kidswrld/plant/soiltest.htm http://edis.ifas.ufl.edu/MENU_SS:SOWASCI http://www.soils.umn.edu/ In Undergraduate Programs, find Course 2125, look at Units 11 & 13.

The best correlations for plant nutrient deficiency and soil tests are obtained for P and K. Correlations between soil tests and N deficiency are not so good. Lime or pH tests are extremely valuable.

Weaknesses inherent in soil test kits are: (1) the difficulty of keeping the glassware chemically clean, (2) the problem of contamination and deterioration of the reagents, (3) misinterpretation of results, and (4) errors in sampling of soil or application of test procedures.

Exercise

The Simplex Soil Test Kit was chosen for use in this laboratory. Another kit will be available in later exercises for optional use.

Test for Lime Requirement

This test is probably the most important one because of the effects of soil acidity on plant nutrient availability and plant growth. It is a reliable test.

The term pH refers to the concentration of hydrogen ions in solution. In fact it is the negative logarithm of the hydrogen ion concentration (see Appendix, p. 10). The pH of pure water is 7.0. Solutions below pH 7 are acidic; those above pH 7 are alkaline. Likewise soils with pH values below 7 are said to be sour or acidic, and those of pH 7 or above are alkaline or sweet. Few plants will grow well in soils with pH values below 4.5 or above 7.5. Most crops grow best in a pH range from 6.0 to 7.0.

Procedure

To test for the acidity or alkalinity of the soil:

1. Weigh 10 grams of soil into a 50-ml beaker.

2. Pour 20 ml of distilled water into the beaker with the soil, and stir the soil and water by swirling the beaker until all of the soil is suspended in the water.

3. Allow the suspension to settle until a clear supernatent solution appears above the solids.

4. Measure the pH of the supernatent solution with a pH meter, which has been calibrated against a pH 7 buffer solution.

a. Place the electrode of the pH meter into the supernatent, being careful not to insert the electrode into the mud.

b. Hold the electrode in the supernatent until the meter indicates that a stable reading can be made. The amount of time needed to obtain a stable reading may be 30 seconds to 1 minute.

5. Record results.

Record of results of pH test (RESULTS)

 

Soil	pH	Texture	Lime needed to raise soil to pH 7.0*
1.	__________	____________________________________	____________________________________
2.	__________	____________________________________	____________________________________
3.	__________	____________________________________	____________________________________
4.	__________	____________________________________	____________________________________

*See the information below and INTERPRETATIONS in the following text.

Lime needed to raise pH of soil one unit

Soil Textural Class	lb/100 sq. ft.	Tons/acre
Sand	5.0	1.0
Sandy loam	6.7	1.33
Loam	10.0	2.0
Silt and clay loams	12.0	2.33
Clay	12.9	2.5

 

To lower the pH unit for most soils

Material	lb/100 sq ft	Tons/acre
Peat	33	6.7
Compost	200 to 250	40 to 50
Manure	67	13.3
Sewage sludge	67	13.3

_____________________________________________________________________________________________

 Tests of Nutrient Deficiency

 Extraction the Soil Sample

 1. Add 3 grams of soil (0.5 teaspoon) to a large glass tube (18 mm x 80 mm) provided with the soil test kit.

 2. Add distilled water (10 ml) to the etched mark on the tube.

 3. Add 1 drop of reagent No. 1.

 4. Stopper and shake the tube well for 1 minute.

 5. Filter the solution into another large glass tube. The filtered solution is called the soil extract.

NITROGEN (Nitrate)

1. Add 1 drop of soil extract to a well in a porcelain test plate.

2. Add 6 drops of reagent No. 2.

3. Comparing the color developed in the well with the blue colors on the nitrate color chart, read the test result in exactly 5 minutes. [Swirl the plate horizontally to blend the color just before reading the result.]

4. Record results (RESULTS)

_______________________________________________________________________________________________

Soil

Test Result

Amount of Fertilizer to Raise Fertility to 100 lb N/acre

	a	b	c	d	e
	ppm nitrate	lb N/acre	N required (100 - b)	Kind of fertilizer to use*	Amount of fertilizer**
1	____________	_______________	__________________	__________________	___________________
2	____________	_______________	__________________	__________________	___________________
3	____________	_______________	__________________	__________________	___________________
4	____________	_______________	__________________	__________________	___________________

*See FERTILIZERS in the following text.
**See INTERPRETATIONS in the following text.

Results of Test (parts per million, read from charts)

NOTE THAT THE RESULTS FROM THE CHART ARE IN POUNDS NITRATE PER ACRE; BE SURE TO USE THE VALUES BELOW, WHICH ARE IN POUNDS NITROGEN PER ACRE.

Reading (ppm)	lb Nitrogen/acre
2	5
5	12
10	25
25	60

 

______________________________________________________________________________________________

PHOSPHORUS (P₂O₅)

 Procedure:

 1. Transfer l ml of soil extract into a small glass tube (15 mm x 73 mm).

 2. Add 5 drops of reagent No. 3 and shake contents.

 3. Add 2 pieces of reagent No 4 (tin) and shake contents.

 4. Read the blue color against the phosphorus color chart within 30 seconds after adding the tin and shaking the tube.

 5. Record results (PHOSPHORUS TEST). (RESULTS)

_______________________________________________________________________________________________

 

Soil

Test Result

Amount of Fertilizer to Raise Fertility to 100 lb P205/acre

	a	b	c	d	e
	ppm P	lb P2O5/acre	P2O5 required (100 - b)	Kind of fertilizer to use*	Amount of fertilizer**
1	____________	_______________	__________________	__________________	___________________
2	____________	_______________	__________________	__________________	___________________
3	____________	_______________	__________________	__________________	___________________
4	____________	_______________	__________________	__________________	___________________

*See FERTILIZERS in the following text.
**See INTERPRETATIONS in the following text.

Results of Test

 NOTE THAT THE RESULTS FROM THE CHART ARE IN POUNDS PHOSPHORUS PER ACRE. BE SURE TO USE THE VALUES BELOW, WHICH ARE IN POUNDS P₂O₅ PER ACRE.

 

Reading (ppm)	lb P2O5/acre
0.5	11
1.0	25
2.5	60
5.0	120

_______________________________________________________________________________________________

POTASSIUM (K₂O)

 Procedure:

 1. Transfer 1 ml of soil extract to a small glass tube.

 2. Add 3 drops of reagent No. 5 and shake contents.

 3. Add slowly, 3 or 4 drops at a time, 1 ml of reagent No. 6, shaking contents after each addition of reagent.

 4. Read the test against the potassium color chart within one minute after addition of last drops of reagent No. 6. Place the bottom of the tube over the black areas (base color spots) on the color chart, and match the colors read through the tube, from top to bottom, with the colors to the left of the base colors.

 5. Record results. (RESULTS)

 ______________________________________________________________________________________________

 

Soil

Test Result

Amount of Fertilizer to Raise Fertility to 200 lb K20/acre

	a	b	c	d	e
	ppm K	lb K2O/acre	K2O required (200 - b)	Kind of fertilizer to use*	Amount of fertilizer**
1	____________	_______________	__________________	__________________	___________________
2	____________	_______________	__________________	__________________	___________________
3	____________	_______________	__________________	__________________	___________________
4	____________	_______________	__________________	__________________	___________________

*See FERTILIZERS in the following text.
**See INTERPRETATIONS in the following text.

 Results of Test

NOTE THAT THE CHART REPORTS RESULTS IN POUNDS POTASSIUM PER ACRE. BE SURE TO USE THE RESULTS BELOW, WHICH REPORT RESULTS IN POUNDS K₂O PER ACRE.

 

Reading (ppm)	lb K2O/acre
0	<30=0
5	65
10	125
20	250

_______________________________________________________________________________________________

Summary of Test Results

 Summarize your soil test results in this table.

Soil

Nutrient Requirement, lb/acre

Analysis of Mixed Commercial Fertilizer or Ratio of Nutrients

	N	P2O5	K2O
1	______________	_______________	_________________	____________________________________
2	______________	_______________	_________________	____________________________________
3	______________	_______________	_________________	____________________________________
4	______________	_______________	_________________	____________________________________

 Use the space below for calculations or notes.

 ___________________________________________________________________________________

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 ___________________________________________________________________________________

 ___________________________________________________________________________________

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 ___________________________________________________________________________________

 ___________________________________________________________________________________

Indicate the kind and amount of organic or natural fertilizers which you have chosen to supply the N, P, and K. See your results on pages 3, 4 and 5. Note whether or not these meet the soil test requirements.

------------------------------------------------------------------------------------------------------------------------------

For Soil 1 ______________

------------N----------------

------------P2O5------------

------------K20------------

 Nutrients from N fertilizer___________________________________________________________________________

 Nutrients from P fertilizer___________________________________________________________________________

 Nutrients from K fertilizer___________________________________________________________________________

 Total nutrients supplied_____________________________________________________________________________

 Total nutrients wanted_____________________________________________________________________________

For Soil 2 ______________

------------N----------------

------------P2O5------------

------------K20------------

Nutrients from N fertilizer___________________________________________________________________________

Nutrients from P fertilizer___________________________________________________________________________

 Nutrients from K fertilizer___________________________________________________________________________

 Total nutrients supplied_____________________________________________________________________________

 Total nutrients wanted_____________________________________________________________________________

For Soil 3 ______________

------------N----------------

------------P2O5------------

------------K20------------

Nutrients from N fertilizer___________________________________________________________________________

Nutrients from P fertilizer___________________________________________________________________________

 Nutrients from K fertilizer___________________________________________________________________________

 Total nutrients supplied_____________________________________________________________________________

 Total nutrients wanted_____________________________________________________________________________

For Soil 4 ______________

------------N----------------

------------P2O5------------

------------K20------------

Nutrients from N fertilizer___________________________________________________________________________

Nutrients from P fertilizer____________________________________________________________________________

 Nutrients from K fertilizer___________________________________________________________________________

 Total nutrients supplied_____________________________________________________________________________

 Total nutrients wanted_____________________________________________________________________________

INTERPRETATIONS OF SOIL TESTS http://www.soils.umn.edu/

 Sample Calculations

___________________________________________________________________________________

 Soil Acidity

pH test result	Soil texture	Lime need to raise soil to pH 7
5.0	sandy loam	(7 - 5) x (1.33) = 2.66 tons/acre
5.0	clay loam	(7 - 5) x (2.33) = 4.66 tons/acre

___________________________________________________________________________________

 Nitrogen

Amount of fertilizer to raise fertility to 100 lb N/acre

Test result	lb N/acre	N required	Fertilizer	Amount of fertilizer
10 ppm nitrate	25	75	Bloodmeal(75lb/12%) =	625 lb/acre
10 ppm nitrate	25	75	Urea (75lb/45%) =	167 lb/acre

___________________________________________________________________________________

Phosphorus

Amount of fertilizer to raise fertility to 100 lb P₂O₅/acre

Test result	lb P2O5/acre	P2O5 required	Fertilizer	Amount of fertilizer
1 ppm P	25	75	Bonemeal (75lb/24%) =	312 lb/acre
5 ppm P	120	0	0	0

___________________________________________________________________________________

 Potassium

Amount of fertilizer to raise fertility to 200 lb K₂O/acre.

Test result	lb K2O/acre	K2O required	Fertilizer	Amount of fertilizer
0 ppm K	0	200	Wood ashes (200 lb/8%) =	2,500 lb/acre
5 ppm K	65	135	Wood ashes (200 lb/8%) =	1,688 lb/acre

 

 ___________________________________________________________________________________

FERTILIZERS http://www.soils.umn.edu/ In course 2125, look at Unit 13.

Major Sources of Nitrogen ___________________________________________________________________________________

Fertilizer and total nutrient composition	----------------------Amount of fertilizer needed to supply------------------------
	-----------------------------------lb of N-----------------------------------------

Material _________________	%N ____________	1 ____________	10 ____________	25 ____________	50 ____________	100 __________
Urea	45	2.2	22	56	111	222
Ammonium nitrate	34	2.9	29	74	147	294
Bloodmeal	12	8.3	83	208	416	833
Animal tankage	8	12.5	125	312	625	1250
Cottonseed meal	6	16.7	167	417	833	1667
Milorganite	6	16.7	167	417	833	1667

Major Sources of Phosphorus

 ___________________________________________________________________________________

Fertilizer and total nutrient composition	----------------------Amount of fertilizer needed to supply------------------------
	-----------------------------------lb of P2O5-------------------------------------

 

Material _________________	% P2O5 ____________	1 ____________	10 ____________	25 ____________	50 ____________	100 ____________
Rock Phosphate*	30	3.3	33	83	167	333
Bone meal	24	4.2	42	104	208	417
Superphosphate	20	5.0	50	125	250	500
Animal tankage	10	10.0	100	250	500	1000
Basic slag	8	12.5	125	312	625	1250
Milorganite	3	33.3	333	833	1667	3333
Cottonseed meal	2.5	40.0	400	1000	2000	4000

Major Sources of Potassium

___________________________________________________________________________________

 

Fertilizer and total nutrient composition	----------------------Amount of fertilizer needed to supply------------------------
	-----------------------------------lb of K2O--------------------------------------

Material _________________	% K2O ____________	1 ____________	10 ____________	25 ____________	50 ____________	100 ____________
Muriate of potash	60	1.7	17	42	83	167
Potassium sulfate	48	2.1	21	52	104	208
Fly ash	12	8.3	83	208	417	833
Wood ashes	8	12.5	125	312	625	1250
Greensand*	7	14,3	143	357	714	1429
Tobacco stems	7	14.3	143	357	714	1429
Granite dust*	5	20.0	200	500	1000	2000
Seaweed	5	20.0	200	500	1000	2000

*Availability of nutrients in rockphosphate, greensand, and granite dust are lower than the total amounts reported here.

___________________________________________________________________________________

APPENDIX

Mixed Commercial Fertilizers

Mixed commercial fertilizers carrying multiple nutrients are available in various analyses or grades, such as 5-10-10, 10-5-10, 10-10-10, 20-20-20, 0-20-20, 45-0-0, 0-45-0, 0-0-60 etc. The first number in the grade stands for the % N, the second for the % P₂O₅, and the third for the % K₂O. One would have to check with the fertilizer dealers to determine which grades are for sale locally. These materials are used to provide the three primary macronutrients (N,P,K) in one fertilizer instead of three fertilizers.

Soil Acidity

The pH Scale

pH is an expression of the hydrogen ion (H+) concentration in the soil. It is often referred to as the soil reaction, that is, whether the soil is acidic, neutral, or alkaline. Acidic soils have a reaction below pH 7.0; neutral soils are pH 7.0; and alkaline soils have a reaction above ph 7.0. Most plants thrive in a soil with a pH between 6.0 and 7.0. Plant survival is very poor or nil below pH 3.5 or above pH 9.0.

Definition of pH

pH = the negative logarithm to the base 10 of the molar H+ concentration in solution (i.e., the soil solution or soil water).

A strongly acidic soil of pH 5.0 would have 10-5M H+ concentration in its soil solution.

A neutral soil of pH 7.0 would have 10-M or 0.0000001 M H+ concentration in its solution.

An alkaline soil of pH 8.0 would have 10-8M or 0.00000001 M H+ concentration in its soil solution.

Effect of pH on plant growth

The main effect of soil reaction between pH 3.5 and 9.0 is on the availability of plant nutrients. Outside this range the concentration of acid, base, or salts affect plant growth adversely.

GUIDE TO THE MINERAL NUTRIENT VALUE OF ORGANIC MATERIALS

_____________________________________________________________________________

-------Materials----------

Total nutrients, percent dry weight*

___________________	N _________________	P2O5 _________________	K2O _________________	Relative availability _________________
Animal tankage	8	10	0.5	Medium
Bone meal, raw	2 to 6	15 to 27	0	Slow
Bone meal, steamed	0	15 to 27	0	Slow
Castor pomace	5	1.8	1	Medium
Cocoa shell meal	2.5	1	2.5	Slow
Compost	1 to 3	0.5 to 1	1 to 2	Slow
Cottonseed meal	6	2.5	1.7	Medium
Dried blood	12	1.5	0.6	Rapid
Fish meal	10	4	0.5	Medium
Fish scrap	3.5 to 12	1 t0 12	0.8 to 1.6	Medium
Guano, bat	5.7	8.6	2	Rapid
Guano, Peruvian	12.5	11.2	2.4	Rapid
Kelp	0.9	0.5	4 to 13	Rapid
Manure, cattle, wet	0.25	0.15	0.25	Slow
Manure, horse, wet	0.3	0.15	0.5	Slow
Manure, sheep, wet	0.6	0.3	0.8	Slow
Manure, hog, wet	0.3	0.3	0.3	Slow
Manure, poultry, wet	3	2.5	1.5	Medium-rapid
Marl	0	2	4.5	Slow
Mushroom compost	0.4 to 0.7	0.5 to 0.6	0.5 to 1.5	Slow
Peat and muck	1.5 to 3	0.25 to 0.5	0.25 to 1	Very slow
Sewage sludge, raw	1 to 6	3 to 7	0 to 1	Slow-medium
Sewage sludge, digested	1 to 5	0.5 to 4	0 to 0.5	Slow medium
Soybean meal	6 to 7	2	2	Medium-rapid
Tobacco stems	2	0.7	6 to 9	Rapid
Urea	42 to 46	0	0	Immediate
Wood ashes	0	1 to 2	1.5 to 10	Rapid

 
The percentage of plant nutrients in the materials is highly variable, and with some materials mean percentages are listed.

Relative availability of plant nutrients is for the principal nutrient during year of application.

Urea fertilizer is a synthetic material.

Potash content of wood ashes depends on the tree species burned. Wood ashes are alkaline, containing approximately 20 to 32% CaO.

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Produced and maintained by Allen Barker
University of Massachusetts, Amherst.