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Reading & Interpreting Soil Test Reports

Unit 1.11 | Part 1 – 433
Lecture 1: Using a Soil Test to Assess Soil Quality

Lecture 1: Using a Soil Test to Assess Soil Quality

Pre-Assessment Questions

1. What is one of the drawbacks of relying on synthetic N-P-K fertilizers?


2. What negative consequences may result from excess nitrate nitrogen in the soil and in
   crops?


3. What role can a soil test play in developing a sound soil management plan?


4. Explain the difference between well-decomposed, stabilized compost and other sources of
   raw organic matter (e.g., cover crops, manure) in terms of its utility as a soil amendment or
   fertilizer


5. What are some of the key soil properties measured in a soil test?


6. Why is it important to ensure that soil pH is maintained in an optimal range?


7. How might one assure that adequate quantities of plant available nitrogen (N) are made
   accessible to crops without excessive fertilization?

A. Critical Terms in Soil Fertility Management

1. Amendment: An organic matter or mineral material applied to the soil to improve or
   maintain the physical, chemical, and/or biological properties of the soil. (Contrast to
   fertilizer, below.)


2. Fertilizer: A readily available and concentrated source of plant nutrients used to supply
   limiting nutrients to growing plants in order to prevent short-term nutrient deficiencies


3. A fertilizer can also be a feedstock for soil microbes, thus improving soil’s physical,
   biological, and chemical properties. Fertilizers such as gypsum/lime can improve soil
   structure; conversely, salt concentrates in fertilizers, e.g., sodium nitrate, can adversely
   affect soil structure. In addition, amendments such as composts or cover crops also supply
   nutrients to plants.

B. The Role of Soil Analysis in Sustainable Agriculture: Reducing Fertilizer Use and
Improving Soil Quality and Human and Environmental Health

1. Soil fertility, plant health, and the resistance and resilience of crop plants to pests and
   pathogens

a) Much like the importance of nutrition to the health of humans, an optimal balance
of available plant nutrients will maintain desirable physical, chemical and biological
properties of agricultural soils. Proper nutrition will also help prevent nutrient-related
plant stress and crop losses through pests, diseases, and poor post-harvest quality.

2. Review of soil nutrients as potential limiting factors in plant growth (see also discussion in
   Unit 2.2, Soil Chemical Properties)

a) Leibig’s Law of the Minimum: “Plant production can be no greater than the level allowed
by the growth factor present in the least amount to the optimum amount for that
factor”

i. Example: Barrel analogy with staves of varying lengths. The shortest stave (the
limiting nutrient) will determine the total volume of water (yield) that can be held.

3. Fertilizer, fertilizer use, and soil testing trends in modern agriculture (see Unit 3.1, The
   Development of U.S. Agriculture)