ANIM2501 Lecture Notes - Lecture 10: Nitrogen Deficiency, Rhizobium, Nitrogen Cycle
Role of Legumes
Nitrogen in Agriculture
- N is essential constituent of plants, which contain 1-4% N, mostly as proteins but also as
many other plant constituents.
- 78% of atmosphere is unreactive N2, higher plants cannot access.
- Nevertheless, 200-250 M tons of atmospheric N fixed annually into usable form.
- - 10% of nitrogen oxides in atmosphere (lightning, forest fires, UV radiation etc)
- - 30% from industrial fertilizers (N2 combined with H at high temp and pressure) (1kg fuel oil
needed for 1kg N) (expensive and use non renewable fuel soures)
- - 60% from biological N fixation by prokaryote bacteria that use enzyme nitrogenase to
convert N2 to ammonia (NH3) e.g. Legume association with rhizobium bacteria.
- After photosynthesis, nitrogen fixation is one of the most important plant biological process.
- The atmosphere is the source of all nitrogen. Commercial fertilizer production simply
processes atmospheric nitrogen into useable form.
- Plants cannot distinguish between sources of nitrogen.
Nitrogen cycle diagram?
Yellowing effect of pasture: Nitrogen deficiency.
Importance of N in crop and Pasture Systems
- Without continued application of fertilizer N, yields of crops and pastures will decline over
time.
- N deficiency limits protein content!
- Regular application of fertilizer N over a long period of time is expensive and can reduce soil
ph.
- Greater use of legume N will be imperative in future
Sources of N for Crop and Pasture
- Soil N
- Fertilizer N
- N fixation from legume- rhizobium symbiosis.
Soil Nitrogen
- Organisms in soil can mineralize n in organic matter at <1% per year. (10-40kg/yr)
- But pastures require 200-400kg N/ha/yr for optimum production
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Document Summary
N is essential constituent of plants, which contain 1-4% n, mostly as proteins but also as many other plant constituents. 78% of atmosphere is unreactive n2, higher plants cannot access. Nevertheless, 200-250 m tons of atmospheric n fixed annually into usable form. 10% of nitrogen oxides in atmosphere (lightning, forest fires, uv radiation etc) 30% from industrial fertilizers (n2 combined with h at high temp and pressure) (1kg fuel oil needed for 1kg n) (expensive and use non renewable fuel soures) 60% from biological n fixation by prokaryote bacteria that use enzyme nitrogenase to convert n2 to ammonia (nh3) e. g. legume association with rhizobium bacteria. After photosynthesis, nitrogen fixation is one of the most important plant biological process. The atmosphere is the source of all nitrogen. Commercial fertilizer production simply processes atmospheric nitrogen into useable form. Importance of n in crop and pasture systems. Without continued application of fertilizer n, yields of crops and pastures will decline over time.
