Tải bản đầy đủ - 0 (trang)
II. Chemical and Physical Characteristics of Fertilizers

II. Chemical and Physical Characteristics of Fertilizers

Tải bản đầy đủ - 0trang

BIOLOGICAL EVALUATION OF FERTILIZERS



267



nutrients-N, P, and K-are usually considered. Formerly, purchases

were commonly made on the basis of price per ton of fertilizer, frequently

without regard to its analysis. A step toward efficient use of commercial

fertilizers is to consider their actual composition, not only as to the

percentage of plant nutrients, but also as to the chemical compounds

making up each fertilizer.

Practically all of the countries in the world have regulations governing

the fertilizer trade that prescribe the quality of the marketed fertilizer.

These regulations usually specify that the producer must express and

guarantee the content of major nutrient elements in a fertilizer as

determined by standard laboratory procedures. The bases of the guarantee, and hence the laboratory procedures, vary from country to country.

The primary purpose of such regulations is to provide consumer

protection, but the producer is also offered a certain degree of protection

in market competition.

Quality control tests must of necessity be relatively simple. Some

of the common tests are based on a solubility measurement of the

nutrient in question. They are indispensable for the purpose for which

they are used, but are not designed to characterize fertilizers completely.

They do not precisely reflect the solubility of phosphorus compounds,

offer little information regarding the form and assemblage of salts in

the fertilizer, and provide little knowledge of physical properties and

other features important in determining the effectiveness of fertilizers.

Jacob and Hill (1953) presented an excellent review of the principles

and methods used in this phase of evaluating phosphate fertilizers. The

official procedures used in the United States, Canada, and Mexico are

described by the Association of Official Agricultural Chemists ( 1955).

The methods used in fourteen countries of western Europe are outlined

in a publication of the Organization for European Economic Cooperation

(1952).

A. COMPOUNDS

PRESENT

IN FERTILIZERS

Inorganic fertilizers are usually composed of one to several solid

phases intermixed rather intimately, Generally, the X-ray and petrographic properties of these phases can be related to definite compounds

and an identification of the solid phases can be made on this basis.

However, in many complex fertilizers, such as ammoniated superphosphates and nitric phosphates, the solid phases are usually mixtures

of colloidal to microcrystalline particles. This makes positive identification

difficult. An additional factor which should be considered is that the

solubility characteristics of the poorly crystallized solid phases may be

different from those of well-defined crystals of the various compounds.



TABLE I

Compounds Present in Nitrogen, Phosphorus, or Potassium Fertilizer Materials Applied Separately or Used as Components of Mixed

Fertilizersn



Fertilizer material



Reprcsentative

grades-%

N-P,O,-K,O



Water

solubility

of N, P,

or K,

( 70 )



N, P, and K compounds prcscnt

Major phases

Minor phases



Major

accessory

compounds

present



!E

. .

0



r

hl



Nitrogen

Ammonium chloride

Ammonium nitrate

Ammonium sulfate

Ammonium nitrate-lime

Calcium cyanamide

Calcium nitrate

Sodium nitrate

Urea



45-0-0



100

100

100



Phosphorus

Ordinary superphosphate



0-20-0



85



0-45-0



87



Ca( H,PO,),*H,O



0-48-0



90



Ca( H,PO,),-H,O



0-54-0



90



Concentrated superphosphate

Wet-process H,PO,



Electric furnace H,PO,

High analysis superphosphate



26-0-0

33.5-0-0

20.5-0-0

20.5-0-0

22-0-0

15.5-0-0

16-0-0



-



100



Clay conditioner



100

100

100



-



CaCO,

CaCO,



-



CaF,

CaSO, *2H,O,

Silica

CaHPO,,

Apatite



CaF,

CaS0, .2H,O,

Silica

Silica

CaF,

Silica



TABLE I (Continued)

Water

solubility

of N, P,

or K,



Major

accessory

compounds

present



Fertilizer material



Representative

grades-%

N-P,0,-K20



Dicalcium phosphate

HC1 process

Electric furnace H,PO,

Calcium metaphosphate



0-40-0

0-48-0

0-62-0



4

3



Fused tricalcium phosphate



0-28-0



<2



Rhenania phosphate



0-33-0



<2



Alpha-Ca,( PO,)

in glass matrix

Ca silico-phosphates



Serpentine phosphate glass



0-22-0



<2



Ca, Mg slico-phosphates



-



Basic slag

Colloidal “clay” phosphate

Phosphate “pebble”

phosphate ore



0-9-0

0-22-0



<2

<1



Ca, silico-carnotite



-



Apatite



Al phosphates



Ca, Na

silicates

Ca, Mg

silicates

Ca silicates

Clay minerals



0-32-0






Apatite



-



CaC03



0-0-60

0-0-48

0-0-23



100

100

100



KC1



-



(%I



5



N, P, and K compounds present



Major phases



Minor phases



CaHPO, -2H20

CaHPO,

Ca( PO,), glass



CaHPO,

CaHPO, .2H20

Beta Ca,P,O,



Silica



-



Quartz

‘Z03



Potassium

Muriate of potash

Sulfate of potash

Sulfomag

a



K2S04



K,SO,. MgSO, .6H,O



Beta Ca,(PO,),,

Apatite



-



-



This information was provided largely by J. R. Lehr, Fundamental Research Branch, TVA, and other sources.



Quartz

R2°3



Type of fertilizer



TABLE I1

Compounds Present in Some Commercial and Expcrimental NP, NK, and NPK Fertilizers0

IienrescntaWater

tive

solubility

N, P, and K compounds prcscnt

grades-%

of P,O,

...N-P,O,-K,O

(%)

Major phases

Minor phascs



Ammoniated concentrated

superphosphate



0



Ammoniated ordinary

superphosphate



5-47-0



50



9-48-0



50



10-20-20

(granulated

with H,SO,)



50



4-14-0



35



6-12-12



NH,H,PO,,

CaHPO, or CaHP04.2€I,0

(NH,)&'O,,

ChHPO,



+



30



-



NH,H,PO,, (N€I,),HPO,,

CaHPO,

NH,C1

KC1 NH,NO,

KNO,

NH,H,PO,,

Basic Ca-phosphate



+



+



8-16-16



65



+



Ammonium phosphate

nitrate



30-10-0



100



-



NH,H,PO,,

Basic Ca-phosphates,

KC1 NH4N0,

NH,Cl + KNO,

(NH,),HPO,, CaHPO,,

Basic Ca-phosphate,

KCl +NH,NO,

KNO,

NH,CI

NH,&PO,,

NH,NO,



Major

accessory

compounds

present



Basic Ca-phosphate"

Unreacted apatite

NH,H,PO,

Basic Ca-phosphate')

Unreacted apatites



SO,, CaF,

SiO,, CaF,



(NH4)2S04



SiO,, CaF,



Basic Ca-phosphate

Unreacted apatites

CaHPO,,

( NH4



Unreacted apatites

Ca( NH4 SO, I2.H2O

CaHPO,,

( NH4



Unreacted apatites

Ca( NH,,K),( SO, ) ,.H,O

NH,H,PO,

( NH4



Unreacted apatities

Ca ( NH4,K)2( SO, I2.H2O

( NH, $PO,



CaSO,

CaSO, .H,O

CaS0,-2H20,

CaF2, SiO,

CaSO4.2H,O,

CaF,, SiO,

CaS04

CaSO,. 1/2 H,O

CaS04-2H,0,

CaF,, SiO,

CaSO,

CaSO,-1/2 H,O



-



‘I’ABLE I1 (Continued)



Type of fertilizer

Ammonium phosphate

nitrate (continued)



Ammonium phosphate

sulfate



ReDresentaWater

tive

solubility

of P,O,

grades-%

N-P,05-K20

(%I



N, P, and K compounds present

Minor phases

Major phases



Major

accessory

compounds

present



27-14-0



100



-



18-18-18



100



-



11-48-0



90



13-39-0



90



16-20-0



90



16-48-0



90



13-13-13



90



Basic Ca phosphateb

Ca( NH, 1 ( SO, 12 - H20

Basic Ca phosphateb

Ca( NH, 12( SO4)2*H20

Basic Ca phosphateb

Ca(NH4)2(S04)2.H20

Basic Ca phosphate*

Basic Ca phosphateb

K,SiF,

Colloidal hydrated

Al, Fe phosphates



100



Diammonium phosphate



21-53-0



Nitric phosphates

HNO, + H3P0, process



12-32-0



40



CaHPO,, NH,H,PO,



14-14-14



20



CaHPO,

KCl NH,NO,

NH,Cl + KNO,



+



-



Basic Ca phosphateb

Unreacted apatites

Ca,H( P0,)3-3H,0

NH,H,PO,

Basic Ca phosphateb

Unreacted anatites



CaSO, * 2H20,

CaF2

CaS0,*2H20,

CaF,

CaS0,-2H20,

CaF,

CaF,,

CaSO, .2H20



-



SiO,, CaF2



SiO,, CaF2



TABLE I1 (Continued)



Type of fertilizer



Ileprcwntative

gracles--c/o

N-P,O,-K,O



Watrr

soluhility

of P,O,



20-20-0



30



CaHPO,, NH,l-i21’04,

NH,NO,



CaHPO, .2H,O

IJnreacted apatites



11-11-11



20



CaHPO,

KC1 NH,NO,

KNO,

NH,Cl

Basic Ca phosphates



NH,H2P0,

CaHPO, 2H20



NH,H,PO,, CaHPO,,

Carbono-apatite



CaSO, 1/2H20

CaSO, .2H,O,

CaCO,, CaF,

CaSO, .2H20

CaCO,, CaF,



( ’/. )



-.



Nitric phosphates (continued)

HNO,

H,SO, process



+



to



HNO,



+ CO,



process



+



-



CaHP0,.2H,O

NH,NO,



12-12-12



10



Carbono-apatite

KCl NH,NO,

NH,Cl

KNO,



NH,H,PO,,



+



+



-



_I__



-



10



N



Calciuni metaphosphate

Hydrolyzed, ammoniated



+



16-14-0



4



Leached zone fertilizer



N, P, arid K compounds present

Major phases

Minor phases

-



CaHPO,



20-20-0



30



Colloidal AlPO, .nH,O

NH,NO,



NH,H,PO,, CaHPO,,

Basic Ca phosphateb



14-14-14



15



Colloidal AlPO, -nH,O

KC1

NH,NO,

NH,Cl+ KNO,



NH,H2P0,, CaHPO,,

Basic Ca phosphateb



16-33-0



15



Microcrystalline

Ca( NH,),P,O,*H,O

NH,NO,



NH,H,PO,

Vitreous Ca ( PO, )

Basic Ca phosphateb

Beta Ca2P,0,



+



,



Major

compounds

present

accessory

SiO,, CaF,,

CaS0,.2H20

CaSO, .1/2H,O

SiO,, CaF,

CaSO, 2H20

CaSO, * 1/2H20



-



CaSO,. 2H,O

Quartz



TABLE I1 (Continued)



Type of fertilizer



RepresentaWater

tive

solubility

grade-%

of P,O,

N-PZOE-KZO

( %)



N, P, and K compounds present

Major phases



Calcium metaphosphate

( continued )



Partially hydrolyzed



13-13-13



50



+



t

o

4



( NH4



w



Partially hydrolyzed



9-18-18



25



-



Vitreous Ca( PO,),

NH,NO, + KC1

NH,CI

KNO,



-



Ca( NH, 1,P,O,.H,O

Vitreous Ca( PO,),

NH,NO,

KC1

NH,Cl

KNO,

(NH,),SO,

Ca( NH, ),P,O,.H,O



+

+



Minor phases



Major

accessory

compounds

present



NH,H,PO,

Beta Ca$,O,



CaSO, .2H20



NH,H2P04

CaHPO,

Beta Ca,P,O,



CaS04.2Hz0



Compounds were identified largely by J. R. Lehr, Fundamental Research Branch, TVA.

Basic Ca phosphate has the optical and physical properties of microcrystalline collophane and a diffuse apatite X-ray diffraction

pattern.

a



b



274



G . L. TERMAN, D. R. BOULDIN, A N D J. R. WEBB



Further studies concerning the identification and solubility of such

complex fertilizers are needed, since the associated phases may markedly

influence the behavior of any given phase when placed in soil and

thereby influence plant response. Hence, relating plant response to the

several solid phases commonly present in the fertilizer is an extremely

complex problem.

Compounds commonly occurring in commercial fertilizers are listed

in Tables I and 11. Nitrogen and potassium compounds are largely water

soluble and comprise a relatively small proportion of the total number

of compounds occurring in commercial fertilizers. A large number of

phosphorus compounds occur, which vary widely in solubility. Jacob

and Hill (1953) have discussed the solubility characteristics and chemical

methods for laboratory evaluation of phosphate fertilizers.

Various phosphorus fertilizers may be grouped into the following

categories of solubility according to AOAC procedures:

1. Water-soluble phosphates. Ammonium phosphates and phosphatenitrates, sodium phosphates, superphosphates, some pyrophosphates and

condensed phosphates, and liquids, including phosphoric acid.

2. Citrate-soluble phosphates. ( a ) Those partially soluble in water

or hydrolyzing rather rapidly to water-soluble forms-calcium metaphosphate, some pyrophosphates, fused potassium phosphates, condensed

phosphorus compounds, etc. ( b ) Those remaining largely insoluble

in water4icalcium and tricalcium phosphates, basic slag, Rhenania

phosphates, etc.

3. Mixtures of I and 2. Partly hydrolyzed calcium metaphosphate,

either ammoniated or not; potassium metaphosphate, ammoniated superphosphates, nitric phosphates, etc.

4. Citmte-insoluble phosphates. Phosphate rocks, "colloidal" phosphates, some precipitated apatites, and complex alkali aluminum-iron

phosphates.

B. DISSOLUTION

OF FERTILIZER^ IN SOILS

When fertilizer granules are placed in soil the rate of dissolution is

largely controlled by the solubility of the constituent compounds, or perhaps more specifically by the difference in vapor pressure of the solution in

and adjacent to the granule and the soil water (Kolaian and Ohlrogge,

1959). With relatively soluble salts such as monocalcium phosphate

[ Ca( HrP04)2.H20],

potassium chloride ( KCI) and ammonium nitrate

( NH4N03) , essentially saturated solutions are generally formed within

the granules, which means that the free energy of water is much lower

in the granule than in the surrounding soil. Water moves toward the

granule as a result of this free energy gradient and in a relatively short



BIOLOGICAL EVALUATION OF FERTILIZERS



275



time (one to several days) the readily soluble components of the

fertilizer have dissolved and moved into the soil. With less-soluble

compounds such as anhydrous dicalcium phosphate ( CaHP04) and

tricalcium phosphate [Ca3( PO4) 2], saturated solutions may also be

formed in the granules, but the saturated solutions are so dilute that no

appreciable free energy gradients exist for water movement and these

compounds may persist for months and years in the soil.

Lawton and Vomocil (1954)studied the influence of granule size,

soil moisture level, and other variables on rates of dissolution of concentrated superphosphate. They found that the rate of dissolution increased

as the granule size was decreased and as the moisture content of the

soil was increased.

C. THENATURE

OF FERTILIZER

REACTIONSWITH SOIL

Nitrogen. As ammonium fertilizers dissolve in the soil solution, much

of the ammonium is sorbed by the soil cation exchange materials in

the vicinity of the granules. This ammonium is held in forms exchangeable with other cations, although some is fixed in nonexchangeable forms.

These reactions may be delayed a few days in the case of urea, which

must first hydrolyze to the ammonium form. Under many soil conditions

the ammonium ions are transformed to nitrate by biological agents over

a variable time period. Nitrate nitrogen is not appreciably sorbed by

most soils and hence is free to move with the soil water and by diffusion.

Both ammonium and nitrate nitrogen are used by soil microorganisms.

These various fates of nitrogen, in addition to utilization by crop plants,

should be considered in any evaluation of nitrogen sources for crops.

Potassium. As potassium salts such as potassium chloride dissolve in

the soil, most of the potassium is sorbed by the exchange minerals and

held in exchangeable and nonexchangeable forms in the vicinity of

the granules until released by some exchange process. As a result,

potassium is somewhat less mobile in most soils than nitrogen. The

chloride ion reacts only slightly with most soils and presumably remains

in solution.

Phosphorus. On addition of soluble phosphates to soil, phosphate

reacts with soil constituents to form less-soluble Compounds distinctly

different from the original fertilizer salts.

Lindsay and Stephenson (195%) studied the reactions of monocalcium phosphate with soil and found that considerable amounts of

iron, aluminum, manganese, and other elements were dissolved by the

acid solution that emerges from granules of superphosphate. Later,

Lindsay and associates ( 1962) identified products resulting from.reaction

of various fertilizer solutions with soil. Some properties of the fertilizer



276



G . L. TERMAN, D. R. BOULDIN, AM) J. R. UTEBB



solutions and some of the reaction products which have been identiiied

are shown in Table 111. The results listed in Table I11 indicate the nature

of the reactions and also how complex some of the reaction products

may be. A careful study of Lindsay et al. suggests that the reaction products formed by different fertilizers in the same soil are likely

to be somewhat different. Differences in the reaction products may

result in differential response of plants to various phosphate fertilizers.

In most soils the soil solution is undersaturated with respect to

dicalcium phosphate, and acid soils are generally undersaturated with

respect to octacalcium phosphate and hydroxyapatite. Hence, these compounds in fertilizers applied to soils would be expected to dissolve

slowly and the phosphate to react with some soil constituent. Moreno

et al. (1960) studied the reactions of dicalcium phosphate dihydrate

in acid soils and concluded that probably iron and aluminum compounds

reacted with the phosphate in solution. However, these reactions were

relatively slow and the soil solution in the vicinity of a granule of

dicalcium phosphate would be expected to remain saturated with this

compound so long as it is present.

Additions of nonphosphatic salts such as NH4N03 and KCl with

phosphate fertilizers influence the dissolution of the phosphates and the

reactions which occur at the granule site and in the soil surrounding

the granule (Starostka and Hill, 1955; Bouldin and Sample, 1958, 1960).

Numerous investigators have found much better utilization of phosphorus

by crops when nitrogen is applied with the phosphate fertilizer (Olson

and Dreier, 1956; Duncan and Ohlrogge, 1958; Miller and Ohlrogge,

1958;Grunes, 1959). Apparently the utilization of fertilizer phosphorus

in the presence of nitrogen is influenced by the nature of the reaction

products formed and by root proliferation in the presence of nitrogen.

The above discussion indicates that when fertilizers are added to

soil, the fertilizer salts dissolve in the soil solution and subsequently

react at least partially with the adjacent soil body. It illustrates the

general principle that, although a fertilizer may be well characterized

chemically and physically, the fertilizer does not retain its identity for

appreciable periods of time following application to the soil. Thus, the

real importance of the chemical and physical properties of the applied

fertilizer depends upon how these properties influence subsequent

reactions with the soil. Even more important, the economic value of the

fertilizer is determined by the capacity of the resulting soil-fertilizer

complex to supply nutrients to plants. Thus, it should be recognized that

properties of both the fertilizer and the soil are equally important, since

the solution emerging from the fertilizer granule or band reacts with

the soil. Consequently, proper evaluation of a fertilizer for crop pro-



TABLE I11

Composition of Saturated Solutions of Certain Fertilizer Compounds and Initial Reaction Products Identified in Filtrates from Soilsa

Composition of saturated

solution at 25°C.

Accompanying cation,

moles/l.



Initial reaction products identi6edb

in filtrates from:

M



pH



Moles/l.



Monocalcium phosphate

[Ca ( H2P04)2-H201



1.48



3.98



Ca 1.44



Monoammonium phosphate



3.47



2.87



NH, 2.87



3.99



1.69



K 1.69



6.25



6.480



NH, 10.9



None



7.98



3.82



NH, 7.64



MgNH,PO,. 6H20

NH,A12(P0,),0H~8H20



Fertilizer



An acid soil

Colloidal

( Fe,A1,X)P0,-nH20

CaHPO, .2H,O

K,Al,H,( P0,)8*18H20

( NH,) ,Al,H,( PO,) s*18H20



( NH4H2P04)



Monopotassium phosphate



K,AI,H, ( PO, ) 18H20



A calcareous soil



5s



8



8



Ca( NH,),P,O,.H,O

CaP,0,.4H20

MgNH,PO, 6H20

Ca2(NH4),( HP0,)3.2H20

Collophane



Data from Lindsay and Stephenson (1959) and Lindsay et al. (1962).

A large number of additional compounds have been found as a result of reacting fertilizer solutions with soil components

and around fertilizer granules in the soil.

c Consisted of 3.40 M phosphorus as orthophosphate and 3.08 M phosphorus as polyphosphates.

a

b



a*



Colloidal

P

( FE,Al,X)PO4.nH20

CaHPO, .2H20

HSK(Al,Fe)3(P04)6*6H20

CaHP0,- 2H20

MgNH,PO,. 6H20

Z

None



( KH2P04



Ammoniated superphosphoric

acid

Diammonium phosphate

[ ( NH, ) 2HPO41



F0



1



Tài liệu bạn tìm kiếm đã sẵn sàng tải về

II. Chemical and Physical Characteristics of Fertilizers

Tải bản đầy đủ ngay(0 tr)

×