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III. Aerobic Soils: Plant Residues and Animal Manures.

III. Aerobic Soils: Plant Residues and Animal Manures.

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ORGANIC AMENDMENTS AND PHOSPHORUS SORPTION

h



5 1.50



c.



h



g 1.50



3



'zpl



v



a



g 1.00

I=

a



Ea



2 0.50



'.OO



2 0.50



z

a:

n



>-



a



f2 0.00



157



None Plot.



Mal.



None Prot.



Mal.



+ 100 mg P/kg



NO P



None Prot.



Mal.



None P r O l



None Prot.



Mel.



None Prot



Mal.



Mml.



+ 400 mg Plkg



NO P



None Prot.



+ 40 mg Pkg



NO P



0.00



MaI.



None Prot.



Mml.



+ 400 mg Plkg



NO P



Figure 7 Yield increases of lettuce in the presence of malic (Mal.)'or protocatechuic (Prot.)

acid. Vertical bars are standard errors. Label " H " represents 2.0 mrnol/kg in the Oxisol or 5.0

mmolikg in the other soils; label "L" represents 0.5 mnlolikg in the Oxisol and 2.0 mmollkg in the

other soils (adapted from Hue. 1991).

Table V



The p H Values of Five Soils Treated with Organic or Inorganic Amendments

after 28-Day Incubation (Adapted from lyamuremye et al., 1995a)

Soil amendment

-



~



~



~



Soil



Control



ManureU



Alfalfao



Wheat straw"



CaCO,*



CaSO,h



Jory (Ultisol)

Mata (Ultisol)

Tolo (Andisol)

Kinigi(Andiso1)

Kibeho(Ultiso1)



5.4

4.7

5.8

4.7

4. I



6.4

6.0

6. I

5.3

5.8



6.7

6.2

6.7

6.1

5.9



5.5

5.3

6.2

5.5



5.8

5.9

6.2



5.3

4.5



5.0



4.8

5.3



5.4

4.6

4. I



-



Amended to m1 at 5% ( w i w ) .

Amended to soil at rate of three times the equivalents needed to neutralize exchangeable Al.



F. WAMUREMYE AND R. P. DICK



158



Theoretically, these reactions should not occur in aerobic soils. However,

because of the heterogeneity of the bulk soils it may be possible that anaerobic

microsites can occur in aggregates. Hue (1992) also suggested that pH may

increase due to ligand exchange between organic acids and hydroxyl groups of

A1 or Fe hydrous oxides as follows:



(gibbaiie)



(tartrate)



The increase in pH causes an increase in cation exchange capacity which

results from formation of negative charges on colloidal fractions.



B. EXCHANGEABLE

ALUMINUM

AND IRON

In acid soils, high levels of exchangeable A1 and Fe play a significant role in

controlling orthophosphate concentration in the soil solution. Thus reduction of

exchangeable A1 and Fe by organic soil amendments could have a significant

effect on P sorption. Iyamuremye er al. (1995a) reported that organic amendments (animal manure and plant residue) reduced exchangeable A1 on high P

fixing soils after a 28-day incubation (Table VI). From a greenhouse experiment

(Fig. 8), it can be seen that the effects of organic material may be temporary, with

effects lasting not longer than 3 months (Hoyt and Turner, 1975). However, this

may be long enough to affect P availability to annual crops and substitute for

lime.



Table VI



Exchangeable A1 in Soils Amended with Organic Residues (5% w/w)

and Incubated for 28 Days (Adapted from Iyamurernye et al., 1995a)

Soil amendment [cmol (+) kg-'1

Soil



Control



Manure



Alfalfa



Wheat straw



Jory (Ultisol)

Mata (Ultisol)

Tolo (Andisol)

Kinigi (Andisol)

Kibeho (Ultisol)



0.426

0.704

nd

0.515



nd"

0.009

nd

0.037

nd



nd

0.004

nd

0.033

nd



0.093

0.296

0.004

0.204

0.321



nd, not detectable



1.080



ORGANIC AMENDMENTS AND PHOSPHORUS SORPTION



159



I



0



1

2

3

4

5

INCUBATION PERIOD (months)



6



Wgure 8 Exchangeable A1 measured in soil over a 6-month period following addition of alfalfwneal, sugar, or peat moss at l .5 or 3.0 % of the soil weight: (a) 1.5% rate, (b) 3% rate. (The

value at 0 months is for the soil without organic material added.) (Adapted from Hoyt and Turner,

1975.)



Several mechanisms may be operating in the reduction of exchangeable metals

when organic residues are added to soils. These reductions may be due to

precipitation of Al ions by OH ions released from the exchange of ligands

between organic anions and terminal hydroxyls of Fe and Al oxides; and/or the

complexation of Al by organic molecules (Hoyt and Turner, 1975; Hue, 1992).

Hue (1992) calculated the lime potential of the organic material used in his

experiment and estimated that the addition of 5 or 10 g poultry manure kg-I was

equivalent to 3.39 and 6.74 cmol Ca(OH), kg-1. Organic acids such as oxalic,

malic, malonic, and citric acid are believed to complex exchangeable Al (Hue et

al., 1986) and were found to be in a greater concentration in forest soil than in

agricultural soils. Iyamuremye et a/. (1995~)detected oxalic, malic, malonic,

maleic, succinic, formic, and acetic acids in the soil solution samples treated

with organic residues. Speciation modeling of manure-amended soil showed that

citric acid had a major role in complexing Al and Fe and affecting P activity in

the soil solution (Iyamuremye et al., 199%).



160



F. IYAMUREMYE AND R. P. DICK



C. PHOSPHORUS

CONTENTOF ORGANIC

RESIDUES

AND PHOSPHORUS

SORPTION

Organic materials generally contain P. This P is susceptible to mineralization

which would release orthophosphate into soil solution. In turn, this orthophosphate could affect P sorption capacity of soils. Singh and Jones (1976) observed

that all organic residues decreased orthophosphate sorption, up to a 30-day

incubation period. They also found that only organic residues with more than

0.3% P decreased orthophosphate sorption and increased desorption up to 150

days. High amounts of orthophosphate were sorbed after 75 days of incubation

when total P content in organic residue was less than 0.3%. They concluded that

P initially fixed began to reappear in the soil solution by the end of a 150-day

incubation period and that use of sorption techniques for predicting P requirement should take into consideration the type and amount of organic matter added

to the soil.

The C:P ratio of organic residues added to soil apparently is important in

determining the effect of organic residues on P sorption. Singh and Jones (1976)

found that when the ratio C / P was > 130, the organic manures did not decrease P

sorption. Figure 9 shows that some organic’materials low in total P (sawdust,

wheat, and corn) increased P sorption in soils, whereas poultry manure, barley

straw, and legume residue decreased P sorption in soils. This same study further

showed that an incubation of 150 days with soil amended with poultry manure

had significantly ,iigher desorption of P than incubation of sawdust-amended

soils. However, Bumaya and Naylor (1988) found that plant residues with P

contents greater than 0.1% applied to soils at a rate equivalent to or greater than

5% (w/w) increased the extractable P and decreased orthophosphate sorption in a

high P sorption soil.



D. BIOLOGICAL

TRANSJXXMATIONS

OF PHOSPHORUS

NVI) FATE

OF PHOSPHORUS

FROM ORGANIC

AMENDMENTS

Studying P nutrition in a pasture/cereal rotation system, McLaughlin and

Alston (1986) found that of the total P applied to the soil, P from plant residues

contributed approximately one-fourth of that supplied by fertilizer; of the total P

in the wheat plant, P from residues supplied approximately one-fifth of that

supplied by the fertilizer. In this study it was found that most of P added through

plant residues accumulates in the microbial biomass pool.

From the above discussions, it is apparent that some P added to soil via

organic residues is converted to inorganic P. However, for mineralization to

occur, soil organic amendments must contain at least 0.2% total P, otherwise net

immobilization may occur (Tisdale et al., 1985; Dalal, 1977). The C:P ratio has



ORGANIC AMENDMENTS AND PHOSPHORUS SORPTION



161



600

150 DAYS

SORPTION

INCUBATION



500



~~~~



0 AL = Alfalfa

A



BA=Barley



0 BE=Beans

400



%

v



A

H



0



+



300



n

W



gm



CH=Check

CO=Corn

PM = Poultry manure

SD=Sawdust

WH=Wheat



200



a

100



1

0.01



1



t



1



1



0.1



I



I



1.o



P IN EQUlLlBRiUM SOLUTION (pg mL1)



Figure 9 Phosphorus sorption following incubation with organic residues for 150 days (adapted

from Singh and Jones, 1976).



been used to predict P mineralization; it is generally accepted that C:P
leads to mineralization whereas C:P >300 leads to immobilization.

One of the mechanisms advanced to explain the reduction of the adsorption

capacity when soil is amended with organic residues is the complexation of

orthophosphate sorption sites by orthophosphate added with or released from

organic residues (Reddy et al., 1980; Iyamuremye et a/., 1995b). Guertal et al.

(1991) reported that orthophosphate sorption was increased in surface soil samples where P had been extracted with resins. This showed that P from organic

residues was occupying the sites of P adsorption.

Both Chauhan et a/. (1979), with grass, and Sharpley et al. (1984), with

feedlot wastes, found that labile and chemisorbed inorganic P increased when

soils were amended with these materials. Iyamuremye el a/. (1995b) showed that

manure and alfalfa increased labile and chemisorbed P in five high P-fixing soils

which represents the P that has reacted with Al and Fe through precipitation

and/or adsorption on surfaces of A1 and Fe compounds in acids soils. This

indicated that soluble inorganic P added with organic residues and/or mineralized residue-P was reacting with the sites of P fixation. These two materials had



F. IYAMUREMYJZ AND R. P. DICK



162



Table VII

Sorption Parameters Calculated from the Langmuir Equation

in Five Soils Treated with Soil Organic (added at 5% w/w or Inorganic

Amendments (Added at Three Times the Equivalents Needed to

Neutralize Exchangeable Al) (Adapted from Iyamuremye el al., 1995a)



Soil amendments



Jory



Mata



Kibeho



Kinigi



Tolo



Manure

Alfalfa

Wheat straw

CaCO,

CaSO,

Control



0,46f'

0.55e

0.88d

1.08~

1.40b

1.58a



Affinity (k) (liters cmol-I)

1.03e

1.05d

3.18b

1.28de

1.02d

4.18b

1.61cd

1.47~

2.98b

1.89bc

1.60~

8.20a

2.37ab

2.82a

5.74ab

2.48a

2.33a

5.91ab



0.18b

0.18b

0.30ab

0.42a

0.32ab

0.37a



Manure

Alfalfa

Wheat straw

CaCO,

CaSO,

Control



3.31b

3.40ab

3.37~

3.35b

3.40ab

3.51a



Adsorption maxima ( b ) (cmol kg-I)

3.03b

3.43d

3.62a

3.24ab

3.59~

3.62a

3.37a

3.65bc

3.62a

3.32a

3.66b

3.69a

3.37a

3.67b

3.74a

3.38a

3.97a

3.79a



2.89d

3.05~

3.40a

2.78e

3.36b

3.31b



Manure

Alfalfa

Wheat Straw

CaCO,

CaSO,

Control



0.76f

0.89e

1.20d

1.30~

1.60b

1.77a



P sorbed at 0.2

1.20~

1.40~

1.70b

1.8Oab

2.00a

2.10a



mg liter-] (cmol kg-l)

1.4Od

2.40bc

0.30b

1.40d

2.60b

0.32b

1.8Oc

2.36~

0.5%

1.85b

3.10~

0.56a

2.40a

2.96a

0.58a

2.35a

3.00a

0.64a



I' Means followed by the same letter within a row are not significantly

different (Tukey's test P < 0.05).



high P content in comparison with wheat straw which was less effective in

increasing labile or chemisorbed P.These results are consistent with calculated P

sorption parameters (Iyamuremye et al., 1995a), where manure and alfalfa had

greater effects than wheat straw in decreasing adsorption maxima and affinity

constants (Table VII).

Mechanisms responsible for organic P mineralization are complex. Laboratory

studies showed that growth of plant roots in soils causes reduction in organic P

content, while organic P increased when phytase or phosphatase preparations

were added to soil in the absence of plants (Jackman and Black, 1952; Thompson

and Black, 1970); the absence of plants caused mineralization of native organic P

(Thompson and Black, 1970). This suggests that the presence of plant roots



ORGANIC AMENDMENTS AND PHOSPHORUS SORPTION



163



and/or soil microflora results in mineralization of soil organic P, whereas the

phosphatase preparation by itself serves as substrate for microflora and results in

immobilization of P as organic P.

Increases in P concentration in the rhizosphere soil solution are attributed to

the hydrolytic cleavage of soil organic P by the action of extracellular phosphohydrolases (Tate, 1984). From these results, phosphatase activity was proposed

as an index of P mineralization (Speir and Ross, 1978).



E. PHOSPHORUS

SORPTION

Early studies (Jensen, 1917) demonstrated that the solubility of Ca, Mg, Fe,

and phosphoric acid in citrus soils of the Riverside district is measurably increased by the addition of green manure, stable manure, or their extracts. Other

researchers (Sibanda and Young, 1986; Struthers and Sieling, 1950) have shown

that addition of organic compounds to the soil prevented P adsorption. Organic

compounds can block exposed hydroxyls on the surface of Fe and Al oxides

(Appelt et a l . , 1975) and decrease P fixation capacity of these oxides (Dalton et

a/., 1952). Gaur (1969) and Stevenson (1986) suggested that organic compounds

form stable complexes with A1 and Fe which result in increased P solubility.

Mnkeni and MacKenzie (1985) found a decrease in P sorption resulting from

addition of plant residues or farm yard manure to upland topsoil and upland

subsoil. However, they observed that the effects depended upon the nature of

phosphate added (orthophosphate or polyphosphates).

Reddy ef a / . (1980), studying soil utilized for animal waste disposal, reported

that the soil that had received high rates of manure sorbed less P and desorbed

more P (Fig. 10). This study showed that an increase in waste loading rates

decreased the adsorption capacity of a soil and increased equilibrium P concentration (EPC) (which is the intercept value at zero P sorption). Estimates of EPC

values were shown to be better related to plant growth than phosphate potential

(Wild, 1950). On the P sorption isotherm in Fig. 10, P at zero sorption is much

higher than 0.2 kg P ml- I , indicating that these soils have sufficient P available

for plant growth [according to Fox and Kamprath (1970), 0.2 pg P ml- I provide

95% of maximum plant growih].

Desorption can also increase with organic amendments. Reddy et al. (1980)

showed that the same soils amended with swine effluent increased P desorption

with increasing P loading, but the amount desorbed depended upon the type of

soil (Fig. 10). For example, at high loading rates, 41 and 23 mg P kg-I soil were

desorbed by Norfolk and Cecil soils, respectively (Reddy et a / . , 1980). These

researchers calculated P sorption parameters of the two soils as a function of

loading rate and soil depth.

The decrease in P sorption by high P-sorbing soils is indicated by the concomi-



F. IYAMUREMYE AND



I64



t



R. P. DICK



SWINE LAGOON EFFLUENT (a)

0-0



CONTROL



0-0



81 kg P ha’ yr‘



A-A



161



P IN SOLUTION (bg rnV)



br



m

3.



v



n

W



m

U



a

w



0



0

3



U



P

Pa



“1



SWINE LAGOON EFFLUENT (b)

(FOUR EXTRACTIONS)

NORFOLK

(+Year

Application)

SERE/



30t //

CECILSERIES



201



a

cn

0



80



160



240



320



PHOSPHORUS APPLIED (kg ha-’ yr’)



Figure 10 (a) Phosphorus adsorption isotherm of the Norfolk soil (0 to 15 cm) as influenced by

application of swine lagoon effluent for a period of 5 years; (b) The sum or P desorbed after four I-hr

extractions with 0.01 M CaClz in Norfolk and Cecil soils (surface 15 crn) as influenced by loading

rate of swine lagoon effluent (adapted from Reddy er al., 1980).



tant decrease of the adsorption maximum and the affinity constant (Reddy et al.,

1980; lyamuremye et al., 1995a), and by the reduction of P required to maintain

0.2 mg liter-’ P in soil solution (Iyamuremye et al., 1995a). Evidence for this is

shown in Table VII. In this case, organic amendments had a larger effect on the

affinity constants and P sorbed at 0.2 mg liter-’ than on the adsorption maxima.

Nonetheless, there was a consistent decrease in adsorption maxima due to organic residues in all five soils.



ORGANIC AMENDMENTS AND PHOSPHORUS SORPTION



165



The reduction of P sorption due to organic amendments in soils is undoubtedly

the cumulative effect of several mechanisms. However, insights into the relative

importance of these mechanisms was reported by lyamuremye et al. (199Sa)

(Table VII), who compared organic amendments with inorganic amendments.

Calcium carbonate decreased exchangeable Al and increased pH, and CaSO,

also reduced exchangeable Al but did not affect soil pH. Both of these inorganic

amendments had less of an effect on sorption constants than the P-rich organic

residues (manure and alfalfa). Calcium carbonate and CaSO, did not increase

Bray I P or total inorganic P, as did organic amendments. Iyamuremye et al.,

(199Sa) concluded that the production of organic acids or other organic complexing agents and effects on P fractions were more important than reduction in

exchangeable metals in affecting P sorption when soils are amended with organic

residues. Furthermore, wheat straw with a low P content also increased P in

equilibrium solution and decreased sorption capacity in most of the soils studied,

which suggested that other compounds or mineralization products in residues,

such as organic acids, are involved in preventing P sorption.



F. ORGANIC

AMENDMENTS

ENRICHED

WITH INORGANIC

AND PHYTOAVAILABILITY

OF PHOSPHORUS

PHOSPHORUS

There is extensive literature on organic amendments and plant nutrition but we

are limiting our discussion to literature specifically related to effects of organic

amendments on P sorption and P availability to plants. Pierre (1938) and Salter

and Schollenberger (1938) discussed the general benefits of animal manure in P

availability and crop productivity.

When organic residues are added to soil, biological mineralization and production of organic P fractions are important in determining the availability to plants

of P originating from organic residues. Results with wheat straw and wheat straw

composts containing labeled P indicated that a relatively greater amount of P is

utilized by plants from compost than from noncomposted material (Fuller and

Nielsen, 1956). On the other hand, results with P-free extracted oat straw showed

that the less decomposed material (oat straw plus KH,PO,) supplied more P to

rye grass than did the compost (oat straw compost plus KH2P0,). The experiments also showed that indigenous soil P is made more available to plants as a

result of decomposition of crop residues such as straw.

Under field conditions Juang (1994) showed that simultaneous addition of rice

compost and N-P-K fertilizers to soil resulted in extractable P levels in soils at

harvest time for corn of 52 mg P kg-1 compared to a sole N-P-K fertilized

treatment of 22 mg P kg- I . Injected dairy manure on a soil fertilizer equivalent

basis showed that P availability to corn (Zea mays L.) varied widely (12-89%

availability) as a function of location and time (Montavalli et a l . , 1989). This



F. IYAMUREMYE AND



166



R. P.DICK



---- MANURED PLOTS



-



UNMANURED PLOTS



0



150



450



600



POUNDS 16% SUPERPHOSPHATE



Figure 11 The relationship between total yield in bushels of corn, wheat, and oats (grain) and

the pounds of 16% superphosphate applied per acre after 57 years of soil amendments and cropping.

The upper curve represents plots receiving 6 tons of manure with added phosphate, the lower curve

represents plots which received 125 pounds of NaNO, and 100 pounds of KCI but no manure. Plots

receive varying amounts of 16%superphosphate as indicated. The average adsorption quotient for the

manured plots is 0.9246 and for the unmanured plots 0.9510 (adapted from Copeland and Merkle,

1941).



high variability is likely related to the importance of biological activity in releasing organic P as a function of soil type and climatic factors. In an alkaline soil

Abbott and Tucker (1973) showed that the main benefit from animal manure to

crops was in P availability (as shown by nutrient content in cotton or barley

tissue). They reported residual effects of P availability for up to 4 years when 22

tons ha-' of animal manure was applied to soils.

Early work by Copeland and Merkel (194 l ) , as illustrated in Fig. 11, showed

that inorganic P could be used more efficiently on soil that had received longterm application of animal manure. A logical extension of this work would

suggest that mixing manure and P fertilizer may have the same effect on the

yield. Indeed, Midgley and Dunklee (1945) reported that if phosphate fertilizers

were added to soils after premixing with farmyard manure, the availability of P

to plants was markedly better than if these materials were added separately.

Later, Widdowson and Penny (1968) showed that a combination of farmyard

manure and inorganic P produced the highest yields of wheat and barley. Giardini



ORGANIC AMENDMENTS AND PHOSPHORUS SORPTION



167



et a / . (1992) showed that mixing poultry manure and fertilizer produced greater

crop yield than did manure or fertilizer alone for some crops. One early explanation was that biologically active manure either exerts a protective effect upon the

soil mineral colloids or helps to release phosphate, or both (Copeland and Merkle, 1941). Much later, Sharif et al. (1974a,b) showed that premixing inorganic

P with farmyard manure before addition to soil markedly increased the uptake of

inorganic P by plants and increased crop yield on P-deficient soil. These authors

hypothesized that organic matter may increase the availability of inorganic P by

suppressing the conversion of inorganic P to Less soluble compounds such as Ca

phosphates in calcareous soil. Over the years, a number of studies have shown

that mixing farmyard manures and inorganic P significantly increased extractable

P in soils (McAuliffe et a / . , 1949; Formoli and Prasad, 1979; Meek et al., 1979;

Geiger et al., 1992).

Plant availability of P from rock phosphate has been enhanced when mixed

with organic material such as compost. Rock phosphate is likely solubilized by

biological activity and production of acids during composting. A number of

studies in India showed that mixing rock phosphate with animal manures or plant

residues followed by composting increased citrate-acid soluble P and/or P availability to plants (Mishra et a l . , 1982; Mathur el al., 1980; Rastogi et al., 1976).

In an alkaline soil, Singh and Amberger (1995) showed that compost enriched

with rock phosphate resulted in greater P uptake by rye grass in the greenhouse

and lower fixation with native Ca than soil amended with soluble inorganic P.



IV. WATERLOGGED SOILS

A. ORGANIC

AMENDMENTS

AND EH

The behavior of P in flooded soil is quite different from that of upland soils and

has been extensively reviewed by Ponnamperuma (1972) and Yu (1985). Recently Sanyal and De Datta (1991) summarized the chemistry of P transformation in

these soils. If the soil oxygen content is low, a series of soil physicochemical

properties such as oxidation-reduction potential, pH, and the forms of some

chemical elements capable of participating in oxidation-reduction reactions ( N ,

S, Mn, Fe, etc.) will be changed (Pan, 1985). Consequently, reduction is the

main chemical reaction driving other biological reactions in saturated soils (Ponnamperuma, 1975).

As the oxygen content decreases, the oxidation-reduction potential drops at

the same time. The oxidation-reduction (Eh) system can be explained as a

chemical reaction in which electrons are transferred from a donor to an acceptor.

Eh is the most important index for characterizing the degree of oxidation or



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