Soil Biology and EcologyUnit 2.3 | 19
Students’ Lecture Outline
- Assessment of fertility needs (also see Unit 1.1, Managing Soil Fertility)
a) Measures of available nitrogen
i. Conventional cropping systems
• Most N provided by additions of fertilizer
• Measurements of nitrate reflect accurately what is available to plants
• Key management decisions are when to apply fertilizer
ii. Cropping systems based on organic matter management
• Soil food web becomes primary source of N derived from organic matter inputs
• Soil analysis in efficiently-managed farming systems may indicate “inadequate”
levels of N at any given time because much of soil N is immobilized
• Cumulative release of mineral N over growing season may match amounts seen in
conventional system
• Managing the timing of mineralization (through tillage, OM quality [e.g., C:N ratio],
incorporation of OM/fertilizers, irrigation) by soil food web becomes more critical
• If managed well, less risk of nutrient loss through leaching or volatilization