BIOLOGICAL TRANSFORMATIONS OF NITROGEN IN SOIL

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Roland Welch
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1 BIOLOGICAL TRASFORMATIOS OF ITROGE I SOIL Animals Animal residues Plant residues Humus Plants Microorganisms itrogen itrous oxide Ammonia Plant roots itrite itrate.e.r. Campbell and H. Lees

2 < < ITROGE CYCLE itrogen Distribution in 10 Virgin Soils and Their Cultivated Counterparts Virgin Soil Cultivated Soil onhydrolyzable ( 6 HCl ) Hydrolyzable Total Ammonium Hexoseamine Amino Acid Unidentified Approximately 0.0 to.5 % of soil is as itrogen. Ina%OCsoil ( Ohio ) the value would be about 0.% itrogen. 1 to %of this is mineralized each year.

3 ITROGE MIERALIZATIO Conversion of organic nitrogen to the more mobile, inorganic state AMMOIFICATO Formation of ammonia from organic matter ITRIFICATIO Oxidation of ammonium to produce nitrate = Organic matter mineralized ( ) i A P L D i = Inorganic itrogen A P L D = itrogen Assimilated by microorganisms = itrogen removed by Plants = itrogen lost via Leaching = itrogen lost via Denitrification

4 The disappearance of I following the addition of a nitrogen poor crop residue is called immobilization. Immobilization is the result of microbial assimilation of inorganic nitrogen and is the converse of mineralization. Ammonium is the most readily assimilated source for soil microorganisms. + H > O > Organic

5 Whether immobilization or mineralization of itrogen occurs depends on the C: ratio. The C: ratio where the two processes are in equilibrium is approximately 0 ( 1.5 % ) C: > 0 is taken from mineral I pool or degradation is slowed Immobilization C: < 0 Mineral is released Mineralization itrogen Factor The number of units of immobilized for each 100 I units of material being decomposed, i.e. the amount of that must be added to avoid immobilization.? = I 100

6 0mg mg Inorganic per g Soil mg 00 mg Weeks Changes in inorganic in soil receiving various quantities of glucose

7 0 C: Ratio 0 0 Wheat Polygonium 10 Alfalfa Weeks Changes in C: ratio during the decomposition of plant residues

8 C: SUMMARY 1 The lowering of the C: ratio from an initailly high value to a lower value occurs during decompostion. The rate and extent of immobilization through microbial assimilation depends on the carbonaceous substances undergoing decay. Whether is immobilized or mineralized depends on the nature of the microbial population. Organic Mineral form Mineraliztion ( BACTERIA < FUGI < ACTIOMYCETES ) Immobilization may be both harmful and beneficial. + Harmful if crop plants also are competing for I Beneficial in serving as a store for of low requirements by plants I I during times

9 FACTORS IFLUECIG MIERALIZATIO 1 Oxygen status Ammonifying population includes both aerobes and anaerobes Moisture Status Wet / dry cycles ph greatest when the soil ph is near neutral Temperature o Optimum is at 0 60 C, which is higher than most biological processes 5 C: ratio

10 FATES OF H + PRODUCED 1. Taken up by plants H +. Taken up by microorganisms H +. Held onto the soil cation exchange sites H + H + H + H +. Is fixed within the clay lattice 5. Reacts with organic matter to form quinone H complexes + = 6. Lost to the atmosphere through volatilization 7. Used as an energy source by chemoautotrophs

11 MIneralization of organic nitrogen and organic carbon are closely related to one another. The ratio of CO C to produced in an unamended soil is relatively constant, ranging from 7 to 15 : 1. i Techniques Used to Predict i Production During a Growing Season 1 Determine the quantity of i produced during a short laboratory incubation period. Establishing what fraction of total organic nitrogen is correlated with nitrogen mineralization rate. O (at time of planting ) prior to side dressing

12 DECOMPOSTIO OF AMIO ACIDS ( removal of amino group ) 1 Transamination (some directly enter TCA cycle ) Oxydative deamination H + H O R C COOH + AD ADH ( H + ) + R C COOH + H H H H O R C COOH + O H O + R C COOH + H H amino acid dehydrogenase O O Reductive deamination H R C COOH + ADH (H ) RCH COOH + H H Hydrolysis H H H + R C COOH + H O R C COOH + H OH 5 Desaturation H R C CH COOH R CH CHCOOH + H H

13 DECOMPOSITIO OF UCLEIC ACIDS HC H C C C H C HC H C CH CH Purine Base Pyrimidine Base (Base Sugar P) Base Sugar P Base Sugar Sugar + Purine ucleic Acid Mononucleotide or Pyrimidine Base

14 Pathway of Metabolism of Purines and Pyrimidines Purine bases Pyrimidine bases H Adenine Cytosine Hypoxanthine Guanine Uracil Xanthine Barbituric acid BUreidopropionic acid Uric acid Urea Malonic acid B Alanine Allantoin Allantoic acid Glyoxylic acid Urea

15 ITRIFICATIO The biological formation (oxidation) of ammonium to produce nitrite and nitrate H O O MICROORGAISMS IVOLVED 1 Obligate aerobes Derive their carbon solely from CO or carbonates Derive their energy from oxidation of H + or O ITROSOMOAS H + O ITROBACTER O O

16 G Valance State H ammonium / O H + itrosomonas H OH hydroxylamine (OH) nitroxyl radical 1/ O 1/ O H O O + H O H + + O nitrite H O itrobacter 18.. O H O hydrated nitrite 1/ O H O +5 O nitrate Postulated Steps in itrification

17 BIOCHEMICAL MECHAISMS OF ITRIFICATIO + + H + 1/ O H OH + H O EVIDECE FOR HYDROXYLAMIE ITERMEDIATE 1 Hydrazine ( H = H ) strongly inhibits H OH O but weakly inhibits H + H OH. Results have shown that H OH can accumulate in small amounts in itrosomonas treated with hydrazine. Oxidation of ammonium is blocked by copper enzyme poisons such as thiourea. However, H OH O is not affected by thiourea.

18 H O O O + H. H + O H O O + O O 1 The oxygen in the nitrate product is from H O, not molecular oxygen This is an example of a hydration ( water addition ) and dehydrogenation ( hydrogen removal ) reaction ITROSAMIE FORMATIO R R R H + O = O + OH R Secondary Amine itrosamine

19 H OH + O HO + H O ( OH ) O O 1/ O + 1/ H O 1 Incubation of hydroxylamine and itrosomonas causes production of O and O O is not an intermediate in nitrification because it is not converted to O Mechanisms are speculative. O may be produced from O still present in the itrosomonas Chlorate ( Dinitrophenol ) inhibits the formation of nitrate from nitrite by itrobacter. This can be used to study the reaction facilitated by itrosomonas. + chlorate blocks reaction H O O The formation of nitrite from ammonium can thus be measured. This reaction is important because it is the rate limiting step.

20 FACTORS AFFECTIG ITRIFICATIO 1 Acidity Aeration Moisture Temperature 5 Organic Matter ITRIFICATIO Beneficial or Harmful? 1 Increases loss of due to leaching Increases loss of due to denitrification Increases risk of O Increases soil acidity toxicity 5 6 May allow easier uptake of by plants It is a necessary intermediate in returning to the atmosphere The end product of fertilizer is nitrate whether the fertilizer is added as urea, anhydrous ammonia, or ammonium nitrate.

21 COTROL OF ITRIFICATIO 1 Control of nitrification inhibitors Use of nitrogen compounds that release slowly because of limited solubility in water or slow rate of microbial decomposition Use of nitrogen compounds coated with material that will delay the release of DESIRABLE CHARACTERISTICS OF ITRIFICATIO IHIBITORS 1 Specific in blocking H + O Able to move with fertilizer through soil ontoxic to plants ontoxic to plant root microenvironment 5 ot easily bio or chemical degradable

22 ITRIFICATIO IHIBITORS POTETIAL ADVATAGES 1 Reduced gaseous loss of Reduced loss of O by leaching and runoff Reduced risk of O toxicity DISADVATAGES 1 Increased gaseous loss of ( H Volatilization ) Increased fixation or immobilization of H Some plants do not use H +, but primarily O

23 MOST EFFECTIVE IHIBITORS OF ITRIFICATIO 1 SERVE Cloro 6( Trichloromethyl ) Pyridine Cl CCl AM Cl Amino Cloro 6Methyl Pyrimidine ATC HC CH H C H Amino 1,, Triazole H CS (ora CS ) Sodium Trithiocarbamate a CS + H O + 5CO ahco + CS 5 DWELL S H 5 C OC C CCl

24 DEITRIFICATIO The reduction of nitrate to nitrite and then to gaseous nitrogen products which are lost from the aquatic or soil system. It is a dissimilatory reduction reaction. ASSIMILATORY ITRATE REDUCTIO O H + The ammonium is used for cell growth. This reaction is oxygen insensitive and is inhibited by reduced compounds DISSIMILATORY ITRATE REDUCTIO O, O This reaction provides energy for growth, but the nitrogen is not used directly for synthesis of microbial products. This reaction is very oxygen sensitive and ammonium insensitive.

25 IMPORTACE OF DEITRIFICATIO 1 Represents a major loss pathway of nitrogen from soils ( 0% ) itrous oxide, a product of denitrification, may lead to destruction of the ozone layer Importance in commercial wastewater treatment plants to reduce nitrate levels A key intermediate, nitrite, readily reacts with secondary amines to produce carcinogenic nitrosamines R R R H + O O + OH R 5 cycling on global basis ote! A key feature distinguishing denitrification from asssimilatory nitrate reduction is the formation of a nitrogen nitrogen bond in denitrification.

26 O O H OH H + ASSIMILATORY REACTIO O O? O DEITRIFICATIO O mg of itrogen O O Time ormal Sequence of Events

27 METHODS OF DETERMIIG DEITRIFICATIO RATES 1 onrecovery of total or 15 nitrogen A. Sensitivity of detection losses are low B. Short term studies not possible C. Analytical errors are important 5 Disappearance of denitrification intermediates A. O or O disappearance ( works only if nongaseous losses are minimal ) B. O disappearance nondisturbing to soil system and specific to one step of denitrification pathway difficult to calculate data ( on a soil basis ) Production of O and A. Sensitive and very precise B. Background of is high, making a natural system difficult to use Inhibition of O reduction by acetylene O is inhibited by C H Denitrification is measured by the accumulation of O in the presence of C H Isolation and enumeration of denitrifiers

28 FACTORS WHICH COTROL DEITRIFICATIO I SOIL 1 Oxygen and redox potential Water content First order to zero order reaction rates occur at low concentrations of O or O Km=7uM O inhibits O so that early intermediates accumulate Concentration of O or O O inhibitions cause greater O production relative to Organic C 5 ph ( optimum is ) 6 Temperature At low ph, more O is produced relative to O can accumulate at low ph Optimum occurs between C. Whether chemical processes are of great importance in this temperature range is still not known. o

29 DECOMPOSITIO OF UREA O Urease H CH H COH HO Urea Ammonium H + CO Carbamate O O H CH +CO H CHCOOH H + CO Allophanic Acid

30 USE OF UREA AS A SOURCE I SOILS Advantages 1 High content (56% ) Low cost of manufacture, transport, storage, and distribution High solubility in water Ease in handling (nonexplosive, noncaking) 5 Suitable for dry blends or in solution blends 6 Can be applied as a foliar spray 7 Used in production of compound fertilizers (Urea phosphates) Disadvantages Rapid hydrolysis to ammonium carbamate 1 Raises ph and causes voloatilization losses of itrite toxicity Seedling germination can be inhibited

31 FACTORS PROMOTIG H VOLATILIZATIO LOSSES 1 ph values > 6 Low moisture content High temperatures Low CEC of soils 5 Addition of highly nitrogenous fertilizer sources without incorporation

32 APPROACHES USED TO DECREASE VOLATILIZATIO LOSSES FROM UREA + = 1 Urease inhibitors Hg, Ag are the most effective inorganic inhibitors Catechol, hydroquinone most effective organic inhibitors Phosphorodiamides, BPT ( n butyl ) thiophosphoric triamide (oxon form is active form ) Slow release urea fertilizers Formation of water insoluble urea compounds ( ureaforms ) Coat urea granule with an inert or water resistant material (sulfurcoated urea ) Conversion to acidic derivative (urea phosphate ) Addition of divalent cations with application of urea

33 (H ) X + CaCO (H ) CO H O + CaX where X = SO or HPO 1. (H ) CO H O H OH + CO and H + + OH H OH H + H O H X + CaCO ( H ) CO H O + CaX X=Cl, O, H PO. at alkaline ph the reaction goes to the right CO ( H ) + H O ( H ) CO H O urea. urease (H ) CO H O + H + H + + CO + H O (H ) CO H O + CaX CaCO + H X soluble salt of divalent cations 7 CaCO precipitation and ph depression ( exchange of Ca for H on exchange sites ) as mechanisms of ammonia volatilization reduction! [ see equations 6 and 7 ] + From Fenn, Taylor, and Matocha, SSSAJ, 1981, 5:777

Soil organic matter composition, decomposition, mineralization and immobilization

Soil organic matter composition, decomposition, mineralization and immobilization SOIL ORGANIC MATTER Substances containing carbon are organic matter. Soil organic matter consists of decomposing plant