International Program in Agricultural Development Studies (IPADS) 20 January 2016 IPADS Soil Fertility Management 4 NITROGEN Department of Global Agricultural Sciences IPADS Kensuke OKADA (akokada@mail.ecc.u tokyo.ac.jp) ipads.jp/soil 1 (Llanos Orientales in Colombia, photo by KO)
IMPORTANCE OF N IN PLANTS
N of primary importance as plant nutrient (Havlin et al. 2005) 17 essential elements 9 elements 8 elements Sodium (Na), Cobalt (Co), Vanadium (Va) and Silicon (Si)
Importance of N in plant (1) Protein Ribulose bisphosphate carboxylase Accounts for 50% of soluble leaf protein in C 3 plants (20 30% of total leaf nitrogen) and 30% of soluble leaf protein in C 4 plants (5 9% of total leaf nitrogen). (Wikipedia)
Importance of N in plant (2) Nucleic acids
Importance of N in plant (3) Chlorophyll N deficiency Yellow and necrotic leaves From lower leaves
N FROM FERTILIZERS
N fertilizers (Havlin et al. 2005) niter 硝石 nitratine チリ硝石
Chilean nitrates
Haber Bosch process 1909 experimental scale 1931 industrial scale N 2 (g) + 3H 2 (g) 2NH 3 (g)
Urea to ammonium Urea hydrolysis : rapid in warm, moist soils (several days) Depending on the ph, NH 3+ volatized Urease is abudant in the soils, especially with high OM It is sometimes slow in cold seasons (p.152)
Slow release nitrogen fertilizers (Havlin et al. 2005)
N CONVERSION IN SOILS
N cycle (Havlin et al. 2005)
N input and loss (Havlin et al. 2005)
Mineralization 1 : Aminization Mineralization : Conversion of organic N to NH 4 + by bacteria (neutral to alkaline soils) by fungi (acidic soils)
Mineralization 2 : Ammonification
C:N ratio effects on mineralization and immobilization (Havlin et al. 2005)
C:N ratio effects on mineralization and immobilization (Havlin et al. 2005)
Nitrification
Factors affecting nitrification Soil ph : 4.5 10 (optimum 8.5) inhibited in acid soils Temperature : Slow in low temperature Soil aeration : accumulation of NH 4+ in paddy field
PLANTS ABSORPTION, TRANSLOCATION AND UTILIZATION OF N
Ion transport pathway in roots
Nitrate Ammonia (Nitrate reduction) NO 3 ー 1 NO 2-2 NH 4 OH(hydroxylamine) NH 3 (1 Nitrate reductase in cytoplasm) (2Nitrite reductase in chloroplast) Irreversible processes take place in roots/leaves depending on the plant species Energy requiring process
Ammonia to Amino acids 1. Glutamine synthetase Glutamate + ATP + NH 3 Glutamine + ADP + phosphate
OTHER N DYNAMICS IN THE SOILS AND THE LOSS
Changes and flow of N from soil to plant (Havlin et al. 2005)
Denitrification Under anaerobic conditions Factors affecting denitrification 1. Decomposable OM 2. Soil water content 3. Aeration 4. Soil ph <5.0 no denitrification <6.0, 6.5 N 2 O is dominant > N 2 5. Temperature
Volatilization of Ammonium
Nitrate leaching
NITROGEN FIXATION IN LEGUMES
N 2 fixation by grain legumes in Africa (Giller et al. 1997)
N 2 fixation by shrubs and trees in the tropics (Giller et al. 1997)
Factors affecting N2 fixation 1. Soil ph 2. Aeration 3. Mineral nutrient status 4. Phytosynthesis and climate
Water logging problem of pigeonpea during rainy season in the semi arid tropics, at a Vertisol field at ICRISAT (K Okada )
Waterlogging of pigeonpea in an Vertisol field (K Okada)
Measuring gas permeability in an Alfisol field (Okada et al. 1991)
Sampling soil air for the measurement of oxygen concentration (Okada et al. 1991) (K. Okada)
(Okada et al. 1991)
Flat bed Ridge and furrow (K Okada)
Distribution of oxygen concentration in the soil air under flatbed configuration vs. ridge furrow configuration (Okada et al. 1991)
Effect of reduced oxygen concentration in soil on the respiration of roots and nodules (Okada et al. 1991) N 2 fixation Respiration Effect on root respiration Effect on nodule respiration Pigeonpea Soybean
ISSUES IN NITROGEN MANAGEMENT
Issues in nitrogen management Alkaline soils Ammonium volatilization Flooding/Poor aeration Denitrification, low N 2 fixation Low temperature Slow mineralization Sandy soils / nitrate accumulation / high rainfall Leaching Residue application Immobilization Excess or deficient N application Need for the decision support system Split plot application