Why have a soil tested?

How to take a representative soil sample

When sampling home gardens, one composite sample consisting of 5-10 subsamples per 100 sq. ft. collected over the planting area should be taken. For larger areas like pastures or tree orchards, first make a detailed map of your area, then divide your map into smaller uniform soil-test areas of a few (1-5) acres each. Label each area clearly on the map by using a combination of letters/numbers that make sense and thus are easy to remember. Each test area should be uniform with regard to soil type or condition. Fields with different slope, soil color, drainage, apparent texture (for example, heavy, light, or A'a) or cropping history should be sampled separately. A soil-test sample for each area should be a composite of 10-15 subsamples.

Soil subsamples consist of 1-inch thick slices of the soil taken to a specified depth, normally 4 inches for no-till fields or established pasture, lawn and turf and 8 inches for conventionally tilled fields. For tree crops (forests, nuts, tree fruits), where possible, collect a surface sample to a depth of 8 inches and a sub-soil sample from 8-24 inches deep. Each sample to be tested should be a thorough mix of the cores taken randomly, say, in a zigzag pattern as shown in Figure 1.

Figure 1. Sampling soil using a zigzag pattern.

Such a sampling technique minimizes the variability that may be present in your field or garden, and allows you to obtain a reasonably representative soil sample.

A specially designed soil probe is often used for collecting soil subsamples (called cores). However, if you do not own a probe, then use a steel or plastic garden spade or shovel to collect soil cores as follows. Dig a hole to the sampling depth, then cut a 1-inch thick slice from the top to bottom of the hole. Take a 1" wide by 1" thich segment of the slice, and place it in a clean mixing bucket, preferably made of plastic.

Plan to collect soil samples two to three months before planting so you will get your test results in plenty of time to plan your liming and fertilization. Depending on workload, the turnaround time at the lab can be up to two-three weeks. Soil in fields or gardens should be tested at least once every two years.

Submitting samples and providing relevant information

After collecting the soil samples, take them to the county extension office in your area or send them directly to the Agricultural Diagnostic Service Center (ADSC) in the College of Tropical Agriculture and Human Resources, University of Hawaii (University of Hawaii, Agricultural Diagnostic Service Center, 1910 East-West Road, Rm 134, Honolulu, HI 96822). To get the most accurate recommendations from your soil test, be sure to fill out a soil information sheet, which is available from your county extension office or the ADSC. A blank soil information sheet is shown in Figure 2.

Figure 2. Soil information sheet used by the ADSC, Univ. of Hawaii.

DATE:_____________________

Name:

Address:

City:

State:

Zip:

Phone:

Fax:

Client ID:

Sample Type:

Sample Location:

Agent:

Address:

City:

State:

Zip:

Phone:

Fax:

Job Control No.:

Sample ID:

*Serial No.:

*Date (m/d/y):

Soil or Mix:

Size of area: sq. ft.:

Acres:

Soil Depth (inches):

Map unit:

Series:

Apparent density: heavy, light, or Aa

Elevation:

Annual rainfall (inches):

Drainage

Slope(%):

Irrigation:

Lime used:

Yr.of application:

Rate:

Type of Lime:

Fertilizer used:

Analysis:

Rate:

Method:

Manure type:

Rate:

Compost:

Rate of compost:

Has rock phosphate been applied?

Plant grown:

Plant to be grown:

Can you till in fertilizer 4-6 inches if necessary?

Bottom land:

Rolling:

Describe the problem & observations:

Send copies to: NRCS ASCS

Objectives for this sample: Diagnosis only

How are soil samples tested?

Soil test results and fertilizer recommendations

Within two to three weeks after you submit your samples to the ADSC, you should receive the test results for your soil along with fertilizer recommendations for your garden or field. The results should include at least pH, and levels of P, K, Ca and Mg in ppm (or mg per kg). A brief interpretation of these levels is also provided as either: very low, low, sufficient, high, very high, or extremely high. An example of the form for the analytical results and interpret-ations is shown in the upper half of Figure 3.

Figure 3. ANALYTICAL RESULTS AND FERTILIZER RECOMMENDATIONS PROVIDED BY THE ADSC

*Soil Lab No:	Interpretation		Plant Lab No:	Interpretation
Soil pH:			Nitrogen (%N):
Phosphorus (ppm) MT or OL:			Phosphorus (%P):
Potassium (ppm K)			Potassium (% K):
Calcium (ppm Ca)			Calcium (% Ca):
Magnesium (ppm Mg)			Magnesium (% Mg)
Salinity (EC, mmhos/cm)			Sulfur (% S)
Zinc (ppm Zn)			Iron (ppm Fe)
Manganese (ppm Mn)			Manganese (ppm Mn)
Copper (ppm Cu)			Zinc (ppm Zn)
Boron (ppm B)			Copper (ppm Cu)
Total N (%)			Boron (ppm B)
Org. C (%)			Molybdenum (ppm Mo)
NH4-N (ppm)			Aluminum (ppm Al)
NO3-N (ppm)			Nitrate (ppm NO3-N)

Total nutrient requirement (lbs/A):		Nitrogen(N):	Phosphorus(P):	Potassium (K):
Fertilizer/Material Options		Fertilizer Amount		Est. Cost
		lbs/1000sq.ft./Crop	lbs/1000sq. ft./mo.	$/1000sq. ft.
Lime
Fertilizer selection
Micronutrient
Other Fertilizers
Comments:

Note: The interpretations are based on the Fact Sheet No. 3 "Adequate Nutrient Levels in Soils and Plants in Hawaii".

Did the recommendation help? To help improve future recommendations, please answer the following questions, photocopy this form and return it to above address (ADSC).

1. Did you need to modify the recommendations? If so, how?
2. Did your plants improve? Please give unit area yield before and after the recommendation was applied.