Teaching Organic Farming and Gardening

Soil Tests and Amendments

Unit 1.11 | 11
Instructor’s Lecture 2 Outline

Lecture 2: Properties Measured in a Soil Analysis

for the instructor

A. Review of the Soil Properties Measured in a Comprehensive Soil Analysis
(see appendix 1, Sample [Blank] Soil Analysis Report)

1. Percent (%) Organic Matter

a) Defined

b) Desirable range for percent organic matter for one’s climate

2. Estimated Nitrogen Release (ENR)

a) ENR defined

b) The accuracy of ENR figures, an estimate of the ENR of one year

c) How to use ENR figures (discussed in Demonstration 3, Nitrogen Budgeting)

i. ENR and annual crops: Use 60% of the ENR figure in nitrogen budgeting

ii. ENR and perennial crops: Use 80% of the ENR figure in nitrogen budgeting

3. Extractable phosphorus (P): Two types of tests are commonly used to illustrate the
   phosphorus availability at different pH levels. Soil phosphorus availability is highly
   
   dependent on soil pH (see phosphorus section in Unit 2.2, Soil Chemistry and Fertility).

a) Available phosphorus (P1) Weak Bray method for soils with pH below 6.2

i. Optimal levels of more readily available phosphorus (P1): 30–40 ppm

b) Olsen sodium bicarbonate extraction for soil with pH above 7.5

i. Optimal levels of phosphorus: 55–65 ppm at pH of 6.2; 12–15 ppm at pH of 7.0

4. Extractable potassium/Potash (K)

a) Optimal levels of available K

i. The optimal level of K in a given soil is 2–5% of the cation saturation (may be
higher in sandy soils)

ii. Total amount (in ppm) to achieve this based on the CEC of the soil (discussed
in greater detail in Demonstration 2, Reading and Interpreting a Soil Analysis
Report)

iii. Optimal levels for course-textured (sandy) soils range from 150–175 ppm; for
heavy-textured (clay) soils, 175–250 ppm

5. Extractable magnesium (Mg)

a) Optimal levels of available Mg

i. The total amount (in ppm) to achieve this is based on the CEC of the soil (discussed in greater
detail in Demonstration 2)

ii. Optimal range of Mg: 100–250 ppm. Soils with Mg levels over 25% of cation
saturation often exhibit drainage problems and require attention.

iii. The optimal level of Mg in a given soil is 10–20% of the cation saturation (10%
on clay soils, 20% on sandy soils)

6. Extractable calcium (Ca)

a) Optimal levels of available Ca

i. The optimal level of Ca in a given soil is 65–75% of the cation saturation

ii. The total amount (in ppm) to achieve this based on the CEC of the soil (discussed in greater detail
in Demonstration 2)