Soil Testing

A professional soil test performed by a laboratory will provide you with the most complete evaluation. Unfortunately, because of variation in soil types, climates, cultivation practices,

Taking a soil sample.
The La Motte soil test kit is a home kit.

SOIL TEST

Date performed:

Performed by:

Recommendations

Test Results per 100 Square Feet

Nitrogen

Phosphorus

Potassium

(6.5 or slightly acid is optimum)

(including texture)

NITROGEN (N), PHOSPHORUS (P), AND POTASSIUM (K)

Pounds of fertilizer to add per 100 square feet. Pounds of pure nutrients added are given in parentheses. Note: The goal is to reduce the nutrient deficiencies in the soil slowly over time. (If you add large amounts of readily available nutrients all at once, nutrients not in short supply in the soil may become unavailable.)

Test Rating

Very High1

High1

Medium High

Medium

Medium Low

Very Low

4.2 lbs alfalfa meal

8.4 lbs alfalfa meal

10.5 lbs alfalfa meal

12.6 lbs alfalfa meal

14.7 lbs alfalfa meal

16.8 lbs alfalfa meal

18.9 lbs alfalfa meal

Phosphorus (P)

Potassium (K)

(.2)

(.15)

4.5 lbs phosphate

1.5 lbs wood

rock or 4.5 lbs

ashes2 and 1.5 lbs

soft phosphate

crushed granite3

(.3)

(.2)

6.8 lbs phosphate

1.5 lbs wood

rock or 13.6 lbs

ashes2 and 2.5 lbs

soft phosphate

crushed granite3

(.35)

(.25)

8 lbs phosphate

1.5 lbs wood

rock or 16 lbs soft

ashes2 and 3.5 lbs

phosphate

crushed granite3

(.4)

(.3)

9 lbs phosphate

1.5 lbs wood

rock or 18 lbs soft

ashes2 and 4.5 lbs

phosphate

crushed granite3

(.45)

(.35)

10.2 lbs phosphate

1.5 lbs wood

rock or 20.4 lbs soft

ashes2 and 5.5 lbs

phosphate

crushed granite3

(.5)

(.4)

11.4 lbs phosphate

1.5 lbs wood

rock or 22.8 lbs soft

ashes2 and 6.5 lbs

phosphate

crushed granite3

(.6)

(.5)

13.6 lbs phosphate

1.5 lbs wood

rock or 27.2 lbs soft

ashes3 and 8.5 lbs

phosphate

crushed granite3

  1. Addition of nutrients at these levels is optional.
  2. Wood ash application should be used with care for soils with a pH above 6.5.
  3. Finely ground.

rainfall, altitude, sun exposure, drainage conditions, the types of crops grown, and cation-exchange capacity, no standard added nutrient formula will work in all situations.

If you can, test your soil for major nutrients and trace minerals, including pH (the acidity or alkalinity level of your soil), before choosing fertilizers. The major minerals, those that plants utilize in relatively large amounts, include nitrogen, phosphorus, potassium, sulfur, magnesium, and calcium. Trace minerals—such as zinc, boron, copper, and iron—are important elements that are required in very small quantities. For professional soil testing, we use the Timberleaf soil testing service.4 It specializes in testing for organic farmers and gardeners, with an emphasis on Biointensive fertility. The service analyzes all soil and plant minerals and the soil's physical characteristics and can provide follow-up review and advice on your year's experience in the garden. If you are unable to arrange a professional soil test, purchase a home test kit. The best such kit is the La Motte kit.5 With the home kit you will be limited to testing nitrogen, phosphorus and potassium content, and pH.

To take a soil sample from your yard, use a nonferrous trowel or a stainless steel spoon to dig a vertical soil slice from 8 inches below the surface. Take samples from 6 to 8 representative areas and mix them together well in a clean plastic bucket. Make sure you do not include residues, such as roots and surface organic litter, in the composite sample. Also, do not sample for 30 days after adding any fertilizers, manure, or compost to the area. The samples normally should be taken at the end of a growing season or just before one. You will need a total soil volume of 1 pound for professional testing or 4 heaping tablespoons for the home test kit. Remember that soil tests can save you a lot of money, since they all guard against overapplication of fertilizers, allow you to account for nutrients already available in your soil for good plant growth, and increase yields.

To use the Timberleaf service, ship your composite sample as instructed in its soil test packet without drying the soil. For a home test kit, let samples dry in a small paper bag in indirect sunlight—not in the sun or an oven. When you are ready to begin testing, follow the included with the kit. Record home test results on a photocopy of the chart on page 50. Once you have completed the test, use the information page 45 to determine a general fertilization plan for your garden.

As you become more skilled, you may want to use John Beeby's book Test Your Soil with Plants to test your soil. This is how people used to learn about their soil's nutrient needs for thousands of years before chemical soil tests became available. Eventually each of us should have a living soil test of plants

  1. Timberleaf, 39648 Old Spring Road, Murieta, CA 92563-5566.
  2. La Motte Chemical Products, Box 329, Chestertown, MD 21620: Model STH.

grown in a small area that is "read" to determine existing nutrient levels in the soil of that area! Until about 100 years ago, this is how farmers determined soil nutrient needs. It will take many years to fully rediscover and develop all these skills.

ANALYSIS OF RECOMMENDED ORGANIC SOIL AMENDMENTS6

N, P, and K refer to three of the major nutrients that plants need. According to law, any product sold as a fertilizer must provide an analysis upon request for these three minerals. Nitrogen contains proteins, is a food source in compost piles, and causes green growth. Phosphorus gives plants energy and is necessary for the growth of flowers and seeds. Potassium aids in protein synthesis and the translocation of carbohydrates to build strong stems. Plants also need a good supply of organic matter to give them additional nitrogen, phosphorus, sulfur, copper, zinc, boron, and molybdenum, and they need 8 other nutrients. Only under ideal conditions do native soil minerals provide these nutrients naturally. Plants need a full meal of nutrients, and as good stewards of the soil we are responsible for providing them. Be aware that laboratory analysis to determine fertilizer amendments does not always show all of the actual needs of the soil plant system. Also, the composition may vary for products from various sources. Be sure to check the analyses on the bags.

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