AREA: Soil and fertilizers

UNIT: Nitrogen

JOB: Introduction to Nitrogen

SITUATION:

OBJECTIVES:

1. To develop the students understanding of the major forms of nitrogen in the soils and the forms of N that plants can readily absorb.
2. To develop the students understanding of what nitrogen deficiency symptoms are.
3. To develop the students understanding of the terminology used when discussing nitrogen.

MOTIVATION

1. Discuss the major forms of nitrogen and the forms of N that plants can absorb.
2. Discuss what the symptoms of nitrogen deficiency are.
3. Discuss the terminology that is often used during discussions concerning nitrogen.

STUDY GUIDES:

1. How much nitrogen is found as NO3-N or NH4-N?
2. How much nitrogen does humus contain?
3. What are deficiency symptoms for nitrogen?
4. What are the ways that nitrogen transforms?
5. What are the factors affecting mineralization and immobilization?
6. What are the factors affecting nitrification?
7. What are the factors affecting denitrification?
8. What are the types of dinitrogen fixation?
9. What are the factors affecting ammonia volatilization?
10. What are some causes of losing nitrogen from the soil?
11. What are some ways to add nitrogen to the soil?

REFERENCE: Lecture Notes for Introductory Soil Science, K.A. Barbarick, pg. 188-193, chapter 15

ANALYSIS:

1. How much nitrogen is found as NO3-N or NH4-N? <1%
2. How much nitrogen does humus contain? 5%, BUT 99+% is found in humus.
3. What are deficiency symptoms for nitrogen? Deficiency symptoms include yellowing (chlososis) along the mid-rib in older leaves; N is mobile in plants.
4. What are the ways that nitrogen transforms?

• Mineralization
• Immobilization
• Nitrification
• Denitrification
• Ammonia volatilization

1. What are the factors affecting mineralization and immobilization?

• C/N of added residue or other material-Need a C/N < 20/1 to achieve net mineralization.

• Aeration-Need O2 for aerobic mineralization. Also, both processes occur under anaerobic conditions but at slower rates.
• Temperature-Optimum is about 35 degrees C.
• Water-Optimum is at field capacity.
• pH-Optimum is near neutral.

1. What are the factors affecting nitrification?

• Aeration-Nitrifying bacteria are aerobes.
• Temperature-Optimum is around 25 degrees C.
• Water-Optimum is at field capacity.
• pH-Optimum is between 7.2 and 7.5.
• Others-Other possible effects could result from salts, trace metals, pesticides, nitrification inhibitors, etc.

1. What are the factors affecting denitrification?

• Aeration and Water-Reduced conditions created by soil saturation or very large heterotrophic microbial activity will enhance denitrification.
• Carbon supply
• NN3-N supply

1. What are the types of dinitrogen fixation?

• Non-biological

1. Lightening can add 1-5 kg N/ha/year.
2. Industrial fertilizer production fixes many Mg of N per year.

• Biological

1. Non-symbiotic N2 fixation adds about 2 kg N/ha/year.
2. Symbiotic

1. What are the factors affecting ammonia volatilization?

• pH-very large losses occur at pH >9.
• Source of NH4-N. Fertilizer or indigenous soil NH4-N could be as high as 20% of that applied.

1. What are some causes of losing nitrogen from the soil?

• Crop removal
• Erosion
• Leaching losses. Ranges from 0 to >200 kg N/ha.
• Volatization. Ranges from 0 to >100 kg/N/ha.

1. What are some ways to add nitrogen to the soil?

• Organic residues and manures
• Fertilizers
• Rainfall
• Biological N2 fixation
• Irrigation water