7b: SOIL COMPOSTING AND TESTING

1. Tissue testing

2. Visual deficiency symptoms

3. Soil testing

Determining Nutrient Needs (3)

Tissue testing

• involves a complete and detailed laboratory analysis of nutrient elements in the plant leaves. This is a very accurate way of assessing how much nutrient the plant has actually taken up from the soil.

• Recommendations are made on the basis of these test results:

  • Backed by research

  • Dependent on plant growth stage and plant part.

1. Nutrient stress may occur before the fertilizer can be applied.

2. It is difficult to determine how much fertilizer to apply.

3. Can be affected by the weather.

Problems with tissue testing are: (3)

Visual deficiency symptoms

• Useful to aid in identifying when plant is deficient in a nutrient.

• They are often difficult to interpret because many symptoms look similar or may look like disease or insect damage.

• When we see deficiency symptoms it is often too late to add additional fertilizer to aid the plants future growth.

Soil testing

is based on the concept that a crop’s response to fertilizer will be related to the amounts of available nutrients in the soil.

1. Good representative sample.

2. Adequate laboratory tests that determine the amount of nutrients the plant can remove from the soil.

3. Considerable experimental work to correlate the soil test results with fertilizer recommendations and actual crop yields.

Good soil testing requires 3 components:

Soil testing

Collecting a soil sample to determine the current nutrient status of the soil

Sufficiency Method of Nutrient Needs

• Uses soil testing to predict fertilizer needs.

• Based on green house and field research.

• Two phased process

  • – Correlation

  • – Calibration

• Soil test is truly a predictive tool.

• Gives soil credit for it’s nutrient providing ability.

Correlation

• Process used to determine if a soil nutrient, as extracted by a soil test, and crop response to added nutrient, are so related that one directly implies the other.

• Process of selecting the best soil test for the soils of the area.

Correlation - process

• Exploratory fertilization trial

  • Greenhouse – a controlled environment with soil homogeneity.

• Trials in field with selected soils.

Correlation - process

Cate-Nelson method

• Determine percentage yield values for each fertilizer rate trial.

• Determine soil test values for nutrient being studied.

• Plot percentage yield vs soil test value

Soil test categories

1. Very low - 90%

2. Low - 75%

3. Medium - 50%

4. High - 30%

5. Very high - 10%

Fertilizers

• To the extent possible, growers do use, and should continue to use, organic waste materials such as manure to replace nutrients lost from the soil.

• Generally, these organic amendments are found to be inadequate for optimal yield, so commercial fertilizers are widely used.

Fertilizer grade

• The numbers on a bag of fertilizer –> “14-14- 14” = guaranteed chemical analysis.

• These numbers indicate the bag of fertilizer contains: 14% N, 14% P2O5, and 14% K2O.

• These numbers –> “14- 14-14” = are referred to as the __.

Composting

A biological process that breaks down organic material (such as grass clippings and leaves) into more stable molecules

1. Mesophilic stage

2. Thermophilic stage

3. Mesophilic (2nd) stage

Stages of Composing Process: (3)

Mesophilic stage

• Brief

• Temperature rises to 40 oC

• Sugars and readily available microbial food sources are rapidly metabolized

Thermophilic stage

• 50 to 70 oC

• Easily decomposed compounds are used up and humus-like compounds are formed

• Frequent mixing essential to maintain oxygen levels and assure even heating of all material

Mesophilic (2nd) stage

• Curing stage

• Temperatures fall back to ambient

• Material recolonized by mesophilic organisms

Benefits from Composting

• Safe storage

• Easier handling

  • Volume reduced 30 to 50%

  • Material more uniform

• Nitrogen competition avoidance

  • No nitrate depression

• Nitrogen stabilization

  • N in organic form

Benefits from Composting

• Partial sterilization

  • Thermophilic stage kills most weed seeds and pathogenic organisms

• Detoxification

  • Most organic compounds are destroyed

• Disease suppression

  • Compost suppresses soil borne diseases by encouraging microbial