NITROGEN
DALAM TANAH
bahan kajian
MK. Dasar Ilmu Tanah
diabstraksikan :
Soemarno, jursn tnhfpub 2012.
Nitrat (NO3-) esential bagi
pertumbuhan tanaman
Protein dalam
sel tanaman
Penyerapan oleh
akar tanaman
Nitrat NO3Dalam tanah
2
Nitrat di-daur-ulang oleh mikroba
Protein
binatang
N-organik dalam tanah
Ammonifikasi
Protein
tumbuhan
Penyerapan oleh
akar tanaman
Ammonium NH4+
Nitrifikasi
Nitrit NO2Nitrifikasi
Nitrat tanah
NO3-
3
SIKLUS NITROGEN (diunduh dari: ecoplexity.org)
4
5
SIKLUS NITROGEN (diunduh dari: http://www.uwyo.edu/virtual_edge/lab24/nitrogencycle.html )
Bentuk-bentuk Nitrogen
•
•
•
•
•
•
•
Urea  CO(NH2)2
Ammonia  NH3 (gas)
Ammonium  NH4+
Nitrat  NO3 Nitrit  NO2 Dinitrogen di atmosfir N2
N-Organik
Cadangan Nitrogen Dunia
Nitrogen
Reservoir
Atmosphere
Metric tons
nitrogen
3.9*1015
Actively cycled
Ocean 
soluble salts
Biomass
6.9*1011
5.2*108
Yes
Yes
Land  organic
matter
 Biota
1.1*1011
2.5*1010
Slow
Yes
No
7
Peranan Nitrogen
• Tumbuhan dan bakteri menggunakan
nitorgen dalam bentuk NH4+ atau
NO3• It serves as an electron acceptor in
anaerobic environment
• Nitrogen is often the most limiting
nutrient in soil and water.
Nitrogen merupakan unsur kunci bagi:
• Asam-asam amino
• Asam-asam nukleat (purine,
pyrimidine)
• cell wall components of bacteria
(NAM).
Siklus Nitrogen
•
•
•
•
•
Ammonifikasi / Mineralisasi
Immobilisasi
Fiksasi nitrogen
Nitrifikasi
Denitrifikasi
The soil nitrogen cycle
(Adapted from Hofman and Van Cleemput, 2004)
Diunduh dari: http://www.fertilizer.org/ifa/HomePage/SUSTAINABILITY/Climate-change/Nitrogen-cycle.html
Bentuk organik N-tanah
Over 90% of the nitrogen N in the surface layer of most soils occurs in organic forms,
with most of the remainder being present as NH4- whichis held within the lattice
structures of clayminerals. The surface layerof most cultivated soils contains
between0.06 and 0.3% N. Peat soils have high N contents to 3.5%. Plant remains and
other debris contribute nitrogen N in the form of: Amino acids
Amino acids exist in soil in several different forms,
like:
As free amino acids
in the soil solution
in soil micropores
As amino acids, peptides or proteins bound to clay
minerals
on external surfaces
on internal surfaces
As amino acids, peptides or proteins bound to humic
colloids
H-bonding and van der Waals' forces
in covalent linkage as quinoid-amino acid
complexes
As mucoproteins
As a muramic acid
Diunduh dari: http://www.humintech.com/001/articles/article_definition_of_soil_organic_matter9.html
BENTUK ORGANIK N-TANAH
Amino sugars
Amino sugars occur as structal
components of a broad group of
substances, the mucopolysaccharides
and they have been found in
combination with mucopeptides and
mucoproteins.
Some of the amino sugar material in soil
may exist in the form of an alkaliinsoluble polysaccharide referred to as
chitin.
Generally the amino sugars in soil are of
microbial origin
.From 5 to 10%of the N in the surface
layer of most soils can be accounted for
in N-containing carbohydrates or amino
sugars.
Diunduh dari: http://www.humintech.com/001/articles/article_definition_of_soil_organic_matter9.html
BENTUK ORGANIK N-TANAH
Nucleic Acids
Nucleic acids, which occur in the cells of all living organisms,
consist of individual mononucleotide units (base-sugar-phosphate)
joined by a phosphoricacid ester linkage through the sugar.Two
types: ribonucleic acid (RNA) anddeoxyribonucleic acid (DNA).
They have pentose sugar (ribose or deoxyribose),the purine: adenine,
guanine and the pyrimidine: cytosine, thymine.RNA contains also
the uracil.
The N in purine and pyrimidine bases is usually considered to
account forless than 1% of the total soil N. Small amounts of N are
extrcted from soil in the form of glycerophosphatides, amines,
vitamins, pesticide and pesticide degradation products.
Diunduh dari: http://www.humintech.com/001/articles/article_definition_of_soil_organic_matter9.html
Transformasi N-tanah
A key feature of the internal cycle is the biological
turnover of N betweenmineral and organic forms
through the opposing processes of
mineralizationand immobilization. The latter leads
to incorporation of N into microbial tissues.
Whereas much of this newly immobilized N is
recycled through mineralization, some is converted
to stable humus forms. The overall reaction leading
to incorporation of inorganic forms of N intostable
humus forms is depicted on the picture. Thus the
decay of plant and animal residues by
microorganisms results in theformation of mineral
forms of N (NH4+ and NO3-) and assimilation of
part ofthe C into microbial tissue (reaction A). Part
of the native humus undergoes a similar fate
(reaction B). Subsequent turnover through
mineralization-immobilization leads to
incorporation of N into stable humus forms
(reaction C). Stabilization of N may also occur
through the reaction of partial decay products of
lignin with nitrogenous constituents (raection D).
Except under unusual circumstances, both
mineralization and immobilizationalways function
in soil, but in opposite direction.
Diunduh dari: http://www.humintech.com/001/articles/article_definition_of_soil_organic_matter9.html
Reaksi kimia ammonia dan
nitrit dengan bahan organik
The fate of mineral forms of N in soil is
determined to some extent bynonbiological
reactions involving
NH4+, NH3and NO2- as depicted in fig.
In addition to NH4+ fixation by clay minerals
(reaction A), NH3 and NO2- react chemically
with organic matter to form stable organic N
complexes(reaction B and C).
The chemical interaction of NO2- with organic
matter may lead to the generation of N gases.
Although both types of reactions can proceed
over a wide pH range, fixation of NH3+ is
favored by a high pH (>7.0).
In contrast, NO2- -organic matter interactions
occur most readily under highly acidic
conditions (pH of 5.0 to 5.5 or below).
Diunduh dari: http://www.humintech.com/001/articles/article_definition_of_soil_organic_matter9.html
C/N RASIO
For surface soils, and for the top layer of lake and marine sediments, the ratio generally falls
within well-defined limits, usually from about10 to 12. In most soils, the C/N ratio decreases
with increasing depth, often attaining values less than 5.0.
Native humus would be expected to have a lower C/N ratio than most undecayedplant residues
for following reasons. The decay of organic residues by soilorganisms leads to incorporation of
part of the C into microbial tissue with the remainder being liberated as CO2. As a general rule,
about one-third of the applied C in fresh residues will remain in the soil after the first few months
of decomposition.
The decay process is accompanied by conversion of organic form of N to NH3 and NO3- and soil
microorganisms utilize partof this N for synthesis of new cells. The gradual transformation of
plantraw material into stable organic matter (humus) leads to the establishmentof reasonably
consistent relationship between C and N. Other factors which may be involved in narrowing of
the C/N ratio include chemical fixation of NH3 or amines by ligninlike substances.
The C/N ratio of virigin soils formed under grass vegetation is normally lower than for soils
formed under forest vegetation, and for the latter,the C/N ratio of the humus layers is usually
higher than for the mineral soil proper. Also the C/N ratio of a well-decomposed muck soil is
lower than for a fibrous peat.
As a general rule it can be said that conditions which encourage decompositionof organic matter
result in narrowing of the C/N ratio. The ratio nearly alwaysnarrows sharply with depth in the
profile; for certain subsurface soils C/Nratios lower than 5 are not uncommon.
Diunduh dari: http://www.humintech.com/001/articles/article_definition_of_soil_organic_matter9.html
SIKLUS N
N2
N2O
NH4
NO2
R-NH2
NO
NO2
NO3
Ammonifikasi
• Nitrogen memasuki tanah melalui
proses dekomposisi protein dalam
bahan organik tanah
Amino acids + 11/2O2  CO2 + H2O + NH3
+ 736kJ
• This process liberates a lot of energy
which can be used by the
saprotrophic microbes
Nitrifikasi
• Nitrifikasi melibatkan dua proses oksidasi
• The ammonia produced by ammonification is an
energy rich substrate for Nitrosomas bacteria
They oxidise it to nitrite:
NH3 + 11/2O2  NO2- + H2O
+ 276kJ
This in turn provides a substrate for Nitrobacter
bacteria oxidise the nitrite to nitrate:
NO3- + 1/2O2  NO3-
+ 73 kJ
• This energy is the only source of energy for
these prokaryotes
• Proses ini bersifat chemo-autotrophs
Fiksasi nitrogen dari atmosfer
• Arus listrik
• Lightning provides sufficient energy
to split the nitrogen atoms of
nitrogen gas,
• Membentuk oksida nitrogen: NOx dan
NO2
21
Ammonifikasi atau Mineralisasi
N2
N2O
NH4
NO2
R-NH2
NO
NO2
NO3
22
Mineralisasi atau Ammonifikasi
• Decomposers: earthworms, termites,
slugs, snails, bacteria, and fungi
• Uses extracellular enzymes  initiate
degradation of plant polymers
• Microorganisms uses:
• Proteases, lysozymes, nucleases to
degrade nitrogen containing
molecules
23
• Plants die or bacterial cells lyse  release
of organic nitrogen
• Organic nitrogen is converted to inorganic
nitrogen (NH3)
• When pH<7.5, converted rapidly to NH4
• Example:
Urea
NH3 + 2 CO2
24
Immobilisasi
• The opposite of mineralization
• Happens when nitrogen is limiting in the
environment
• Nitrogen limitation is governed by C/N
ratio
• C/N typical for soil microbial biomass is
20
• C/N < 20 Mineralization
25
• C/N > 20 Immobilization
Fiksasi Nitrogen
N2
N2O
NH4
NO2
R-NH2
NO
NO2
NO3 26
Fiksasi Nitrogen
• Energy intensive process :
• N2 + 8H+ + 8e- + 16 ATP = 2NH3 + H2 +
16ADP + 16 Pi
• Performed only by selected bacteria and
actinomycetes
• Performed in nitrogen fixing crops
(ex: soybeans)
27
Fiksasi N Biologis
Treatments
Yield / g
Oats
No nitrate & sterile soil
Peas
0.6
0.8
Nitrate added & sterile soil
12.0
12.9
No nitrate & non-sterile soil
0.7
16.4
11.6
15.3
Nitrate added & non-sterile soil
28
Bintil Akar
Alafalfa (Medicago sativa)
USDA - ARS
University of Sydney
Organisme prokaryotik mampu fiksasi N
• These organisms possess the nif gene complex which
make the proteins, such as nitrogenase enzyme, used in
nitrogen fixation
• Nitrogenase is a metalloprotein, protein subunits being
combined with an iron, sulphur and molybdenum complex
• The reaction involves splitting nitrogen gas molecules and
adding hydrogen to make ammonia
N2  2N
2N + 8H+  NH3 + H2
- 669 kJ
+ 54 kJ
• This is extremely energy expensive requiring 16 ATP
molecules for each nitrogen molecule fixed
• The microbes that can fix nitrogen need a good supply of
energy
Pem-fiksasi Nitrogen
• Cyanobacteria are nitrogen fixers that also fix
carbon (these are photosynthetic)
• Rhizobium bacteria are mutualistic with
certain plant species e.g. Legumes
• They grow in root nodules
• Azotobacter are bacteria associated with the
rooting zone (the rhizosphere) of plants in
grasslands
31
Mikroorganisme Fiksasi N
•
•
•
•
•
Azobacter
Beijerinckia
Azospirillum
Clostridium
Cyanobacteria
• Require the
enzyme
nitrogenase
• Inhibited by
oxygen
• Inhibited by
ammonia (end
product)
32
Laju Fiksasi Nitrogen
N2 fixing system
Rhizobium-legume
Nitrogen Fixation (kg
N/hect/year)
200-300
Cyanobacteria- moss
30-40
Rhizosphere
associations
Free- living
2-25
1-2
33
34
Aplikasi ke Lahan Basah
•
•
•
•
•
Occur in overlying waters
Aerobic soil
Anaerobic soil
Oxidized rhizosphere
Leaf or stem surfaces of plants
35
Fiksasi oleh Bacteri
• Proses ini dapat terjadi dalam
tanah
• Is absent from low pH peat of
northern bogs
• Cyanobacteria ditemukan pada
tanah-tanah tergenang
Nitrifikasi
N2
N2O
NH4
NO2
R-NH2
NO
NO2
NO3
37
Nitrifikasi
Dua tahapan reaksi yang terjadi bersamaan :
• 1rst step catalyzed by Nitrosomonas
2 NH4+ + 3 O2  2 NO2- +2 H2O+ 4 H+
• 2nd step catalyzed by Nitrobacter
• 2 NO2 + O2  2 NO3
Nitrifikasi
• pH Optimal pH : 6.6-8.0
• Kalau pH < 6.0  laju reaksinya lambat
• Kalau pH < 4.5  Reaksinya terhambat
In which type of wetlands do
you thing Nitrification occurs?
Denitrifikasi
N2
N2O
NH4
NO2
R-NH2
NO
NO2
NO3
40
Denitrifikasi
• Removes a limiting nutrient from the
environment
• 4NO3- + C6H12O6 2N2 + 6 H20
• Dihambat oleh O2
• Tidak dihambat oleh amonia
• Reaksi mikrobiologis
• Nitrat merupakan aseptor elektron
41
PERANAN NH4 DALAM
SIKLUS NITROGEN
43
Surface water
Oxidized
layer
Reduced
soil layer
Low
[NH4]
Biodegradation
Slow Diffusion
C/N <20
C/N >20
[NH4]
HIGH
Surface
water
nitrification
Low
[NH4]
Oxidized
layer
Reduced
soil layer
Slow Diffusion
[NH4]
HIGH
[NO3] high
N2
Surface
water
Oxidized
layer
Reduced
soil layer
[NO3] high
Leaching
[NO3] Low
Denitrification
Dampak Kegiatan Manusia
Atmospheric Nitrogen
Atmospheric
fixation
Out
gassin
g
Industrial
fixation
Plant
protein
Biological
fixation
Soil organic
nitrogen
Ammonium
NH4+
Nitrate NO347
Sumber: © 2008 Paul Billiet ODWS
Fiksasi N secara Industri
• Proses Haber-Bosch
N2 + 3H2  2NH3 - 92kJ
• Proses Haber menggunakan katalis besi
• Suhu tinggi (500°C)
• Tekanan tinggi (250 atm)
• The energy require comes from burning
fossil fuels (coal, gas or oil)
• Hydrogen is produced from natural gas
(methane) or other hydrocarbon
Sumber-sumber Fiksasi Nitrogen
Sources of fixed nitrogen
Production / M tonnes a-1
Biological
175
Industrial
50
Internal Combustion
20
Atmospheric
10
Sumber; © 2008 Paul Billiet ODWS
Eutrofikasi
• Pengkayaan hara ekosistem perairan
• Nitrat dan ammonia mudah larut dalam air
• Kedua bentuk nitrogen tersebut mudah tercuci
dari tanah
• Sehingga tanah –tanah ini cenderung defisien
nitrogen
• When fertiliser is added to these soils it too will
be washed out into water bodies
• There algae benefit from the extra nitrogen
• This leads to a serious form of water pollution
Eutrophication is the enrichment of an ecosystem with chemical nutrients,
typically compounds containing nitrogen, phosphorus, or both.
Source: http://www.pbl.nl/en/index.html
Diunduh dari: http://biogenicsilica.blogspot.com/2010/08/eutrophication.html
Bahaya Eutrofikasi
. Many lakes around the world have been effected by discharges of nutrients directly into them.
In severe cases this can lead to the process of eutrophication. Inputs of nutrients from sources
such excessive over use chemical fertilizers on agricultural land can lead to accelerated growth of
algae creating massive blooms. Some of these blooms can be are toxic.
Diunduh dari: http://sciencebitz.com/?page_id=597
Kerusakan Ekosistem Danau
Berkurangnya oksigen terlarut
Peningkatan
kandungan nitrit
NO3-  NO2-
Death/emigration
of freshwater
fauna
Methaemoglobinaemia in infants
Stomach cancer link
(WHO limit for nitrates 10mg dm-3)
Masa depan Industri Fiksasi N
• Food production relies heavily upon synthetic
fertilisers made by consuming a lot of fossil
energy
• Produksi pangan menjadi lebih mahal
• Nitrogen fixing microbes, using an enzyme
system, do the same process at standard
temperatures and pressures essentially using
solar energy
• Jawab: Rekayasa genetik fiksasi N biologis?
54
Memperbaiki aplikasi nitrogen
• Kebutuhan pupuk sintetis dapat dikurnagi dengan
perbaikan teknologi budidaya tanaman
• Menghindari penggunaan pupuk mudah larut pada tanah
berpasir untuk mencegah pencucian hara
• Rotating crops permits the soil to recover from nitrogen
hungry crops (e.g. wheat)
• Adding a nitrogen fixing crop into the rotation cycle
• Ploughing aerates the soil and reduces denitrification
• Draining water logged soil also helps reduce denitrification
Denitrifikasi
• Nitrat dan nitrit dapat digunakan sebagai
sumber oksigen oleh bakteri Pseudomonas
• Favourable conditions: Cold waterlogged
(anaerobic) soils
2NO3-  3O2 + N2providing up to 2385kJ
2NO2-  2O2 + N2 
• The liberated oxygen is used as an electron
acceptor in the processes that oxidise organic
molecules, such as glucose
• Mikroba ini bersifat “heterotroph”
Beberapa Hal Penting
• Pemupukan nitrogen membantu
pertumbuhan tanaman
• Keberadaan mikroba tanah bermanfaat bagi
pertumbuhan tanaman
• Bakteri bintil bersimbiosis dnegan kaar
tanamna legume memfiksasi nitrogen
HASIL-HASIL
PENELITIAN
. Nitrogen deposition and climate effects on soil nitrogen availability: Influences of
habitat type and soil characteristics
E.C. Rowe , B.A. Emmett , Z.L. Frogbrook , D.A. Robinson , S. Hughes
Science of The Total Environment. Volume 434, 15 September 2012, Pages 62–70
The amount of plant-available nitrogen (N) in soil is an important indicator of eutrophication of
semi-natural habitats, but previous studies have shown contrasting effects of N deposition on
mineralisable N in different habitats. The stock of readily mineralisable N (Nrm) was measured in
665 locations across Britain from a range of intensively and extensively managed habitats,
allowing N availability to be studied in relation to soil and vegetation type, and also to variation in
climate and in reactive N deposition from the atmosphere. Mineralisable N contents were
correlated with deposition in extensively managed habitats but not in intensively managed
habitats. The following statements apply only to extensively managed habitats. All habitats
showed a similar increase in Nrm with N deposition. However, soil characteristics affected the
relationship, and soil carbon content in particular was a major control on mineralisation. The Nrm
stock increased more with N deposition in organic than in mineral soils. The nitrate proportion of
Nrm also increased with N deposition but, conversely, this increase was greater in mineral than in
organic soils. The measurements could be used as indicators of eutrophication, e.g. deposition
rates of over 20 kg N ha− 1 y− 1 are associated with nitrate proportions of > 41% in a mineral soil
(2% carbon), and with Nrm stocks of over 4.8 kg N ha− 1 in an organic soil (55% carbon). Both Nrm
and nitrate proportion increased with mean annual temperature of the sampling location, despite
consistent incubation temperature, suggesting that increasing temperatures are likely to increase
the eutrophying effects of N pollution on semi-natural ecosystems.
Diunduh dari: http://0-www.sciencedirect.com.precise.petronas.com.my/science/article/pii/S0048969711014914
Soil Moisture Control of Nitrogen Fixation Activity in Dry Tropical Casuarina
Plantation Forest
Alok K. Srivastava , R.S. Ambasht
Journal of Environmental Management. Volume 42, Issue 1, September 1994, Pages 49–54
Nitrogenase activity nitrogen accretion to soil in two age groups of Casuarina
equisetifolia plantation forest have been assessed.
Our findings show that, in the summer months, the nitrogenase activity is at a
minimum but, with the onset of rain even though it continues to be very warm, new
nodulation starts and the peak of N2-fixing activity is soon reached. Multiple
regression analysis showed soil moisture in the warm temperature condition as the
major factor controlling the nitrogenase.
Based on our finding, we are tempted to suggest that if adequate moisture through
judicious irrigation management is made available in summer, the nodulation could
be hastened and N2 fixation activity could be prolonged at a high level during 4
months of summer and 4 months of rains.
Diunduh dari: http://www.sciencedirect.com/science/article/pii/S0301479784710590
. RELATION OF AVAILABLE SOIL NITROGEN TO RICE YIELD.
Dolmat, M. T.; Patrick, W. H., Jr.; Peterson, F. J.
Journal Soil Science 1980 Vol. 129 No. 4 pp. 229-237
The relationship between the available soil nitrogen and rough rice yields was then investigated. Total
soil nitrogen varied widely, ranging from 540 to 5460 parts per million. The average percentage recovery
of total soil nitrogen (representing the available soil nitrogen), as determined by the various methods
used, also ranged widely, from as high as 16.74 percent, by the hot alkaline permanganate method, to the
lowest value of 1.08 percent, by boiling soils in 0.01 M CaCl2 solution.
Good correlation coefficients were obtained, especially among the anaerobic incubation and each of the
other extraction methods used. The acid hydrolysis method correlated the least with the other extraction
methods. Highly significant correlation coefficients were obtained between the rough rice yields from
the untreated plots (plots that received no nitrogen) and the available soil nitrogen determined by all the
extraction methods.
The best correlation was obtained with the anaerobic incubation method (r = 0.622). The rough rice yield
in plots receiving 56 or more kilograms of nitrogen per hectare did not exhibit a significant relationship
with the available soil nitrogen. Relationships between the rough rice yields at zero and 28 kg/ha N and
the available soil nitrogen, as determined by the anaerobic incubation method, were better described by
curvilinear models than by linear ones. The relationship was also established between yield increase
from application of 112 kg/ha N (the level of nitrogen generally considered near optimum for rice in
Louisiana) and available soil nitrogen determined by the anaerobic incubation method. With some
reasonable degree of accuracy, yield increase could be predicted from the graph signifying this
relationship.
Diunduh dari:
http://www.cabdirect.org/abstracts/19801955633.html;jsessionid=587B71ACB1ACE2A89AB75354744EEFF9?gitCommit=4.13.19-9-g409ea67
. Nitrogen Dynamics and Indices to Predict Soil Nitrogen Supply in
Humid Temperate Soils
Mervin St. Luce , Joann K. Whalen , Noura Ziadi , Bernie J. Zebarth
Advances in Agronomy. Volume 112, 2011, Pages 55–102
In humid temperate regions, soil N supply is dominated by in-season N mineralization because plantavailable N (NH4–N and NO3–N) is transformed to nonlabile forms or lost from the soil–plant system
during fall and winter.
The microbially mediated reactions that generate the soil N supply in agroecosystems are affected by
system-specific conditions, including soil properties, agricultural management (crop rotation, tillage
system, organic amendments), and most importantly, climate.
Potentially mineralizable N (N0) determined from long-term soil incubation is regarded as the
standard measure of soil N mineralization potential and may provide a good approximation of the soil
N supply. However, this method is time consuming and not practical for routine use.
Several chemical methods to estimate the N mineralization potential of soils are discussed in this
chapter.
The major limitation of chemical methods is that they cannot simulate the microbial-mediated release
of plant-available N under field conditions. Consequently, any single chemical method may not be a
good predictor of soil N supply. Thus, we suggest a holistic approach to estimate soil N supply in
humid temperate regions, which involves (1) the use of a combination of N indices together with
weather data and (2) identification and quantification of a specific fraction (s) of organic N that is the
dominant contributor (s) to N supply in a particular system.
Diunduh dari: http://www.sciencedirect.com/science/article/pii/B9780123855381000020
. Nitrogen Dynamics and Indices to Predict Soil Nitrogen Supply in Humid
Temperate Soils
Mervin St. Luce , Joann K. Whalen , Noura Ziadi , Bernie J. Zebarth
Advances in Agronomy. Volume 112, 2011, Pages 55–102
Illustration of the nitrogen cycle in soil.
Diunduh dari: http://www.sciencedirect.com/science/article/pii/B9780123855381000020
. Nitrogen transformations with special reference to gaseous N losses from zerotilled soils of Saskatchewan, Canada
M.S. Aulakh , D.A. Rennie
Soil and Tillage Research. Volume 7, Issues 1–2, May 1986, Pages 157–171
Cumulative gaseous N losses (N2 O + N2) measured with acetylene inhibition-soil core technique
ranged from 1 to 7 kg ha−1 year−1 N for CT and from 12 to 16 kg ha−1 year−1 N for ZT fields. In
both CT and ZT, gaseous N losse were 2–5 times higher for a wheat-fallow than a continuouswheat rotation. The denser surface soil and consistently higher moisture content of ZT fields
were identified as the main reasons for higher rates of denitrification.
The potential denitrification rates were markedly higher in ZT and the population of denitrifiers
was up to six times higher than in the CT fields. Crop residues doubled the gaseous N losses.
Temperature above 5°C did not alter denitrification rates nor did a wide range of mineral N.
The contribution of lower soil horizons towards gaseous N losses was negligible. Mole fraction
of N2O [N2O/(N2O + N2)] showed a reverse relationship with soil moisture and varied from 28 to
98% in the total gaseous N products. About 35% of autumn-applied 15N-labelled fertilizer N was
lost via denitrification and 7–20% became immobilized by the following spring. Leaching was
not responsible for the lower efficiency of fertilizer N. Due to adequate N fertilization and good
straw mulch conditions, yield, N uptake and protein content of wheat were highest in the ZT
system.
The ZT system was also efficient in conserving more moisture from over-winter snowfall and
rains.
Diunduh dari: http://www.sciencedirect.com/science/article/pii/0167198786900152
. Effects of soil water content and nitrogen supply on the productivity of Miscanthus x
giganteus Greef et Deu. in a Mediterranean environment
Cosentino SL, Patane C, Sanzone E, Copani V, Foti S
Industrial Crops and Products. [2007, 25(1):75-88]
Miscanthus x giganteus is one of the most promising biomass crops for non-food utilisation. Taking
into account its area of origin (Far East), its temperature and rainfall requirements are not well
satisfied in Mediterranean climate. For this purpose, a research was carried out with the aim of
studying the adaptation of the species to the Mediterranean environment, and at analysing its
ecophysiological and productive response to different soil water and nitrogen conditions. A split plot
experimental design with three levels of irrigation (I1, I2 and I3 at 25%, 50% and 100% of maximum
evapotranspiration (ETm), respectively) and three levels of nitrogen fertilisation (0 kg ha-1: N0, 60
kg ha-1: N1 and 120 kg ha-1: N2 of nitrogen) were studied.
The crop showed a high yield potential under well-watered conditions (up to 27 t ha-1 of dry matter).
M. x giganteus, in Mediterranean environment showed a high yield potential even in very limited
water availability conditions (more than 14 t ha-1 with a 25% ETm restoration). A responsiveness to
nitrogen supply, with great yield increases when water was not limiting, was exhibited. Water use
efficiency (WUE) achieved the highest values in limited soil water availability (between 4.51 and
4.83 g l-1), whilst in non-limiting water conditions it decreased down to 2.56 and 3.49 g l-1 (in the
second and third year of experiment, respectively). Nitrogen use efficiency (NUE) decreased with the
increase of water distributed (from 190.5 g g-1 of I0 to 173.2 g g-1 of I2); in relation to N
fertilisation it did not change between the N fertilised treatments (N1 and N2), being much higher in
the unfertilised control (177.1 g g-1). Radiation use efficiency (NUE) progressively declined with the
reduction of the N fertiliser level (1.05, 0.96 and 0.86 g d.m. MJ-1, in 1994, and 0.92, 0.91 and 0.69
g d.m. MJ-1, in 1995, for N2, N1 and N0, respectively).
Diunduh dari: http://europepmc.org/abstract/AGR/IND43888538