Soil Phosphorus and Potassium RNA Chapter 14 1 2 Phosphorus and - - PowerPoint PPT Presentation

2018/5/29 1

Soil Phosphorus and Potassium

Chapter 14

1

Role of P in Plant Nutrient and Soil Fertility

• ATP
• DNA
• RNA

2 3

Phosphorus and Plant Growth

• Adequate phosphorus nutrition enhances many aspects
• f plant physiology, including the fundamental

processes of photosynthesis, nitrogen fixation, flowering, fruiting (including seed production), and maturation.

• Root growth, particularly development of lateral roots

and fibrous rootlets, is encouraged by phosphorus. (小 根)

• In cereal crops, good phosphorus nutrition strengthens

structural tissues such as those found in straw or stalks. (穀類)(稻草、麥桿)(stalk=stem)

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腐朽,摧毀 直立的

Crushing strength of stalk: 是指要施與多少壓力才能讓植物倒伏之意

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The Phosphorus Problem in Soil Fertility

• The total phosphorus level of soil is low, usually no more

than 1/10 to ¼ that of N, and 1/12 that of K.

• The phosphorus compounds commonly found in soils are

unavailable for plant uptake, often because they are highly insoluble.

• When soluble sources of phosphorus, such as those in

fertilizers and manures, are added to soils (changed to unavailable forms) and in time form highly insoluble compounds.

• Fixation reactions in soils may allow only a small fraction

(10 to 15%) of the phosphorus in fertilizers and manures to be taken up by plants.

6

The Phosphorus Problem in Soil Fertility

Some farmers apply two to four times as much phosphorus as is removed in the crop harvest. Repeated over many years, such practices have saturated the phosphorus-fixation capacity and built up the levels

• f available phosphorus in

many agricultural soils.

7

Effects of P on Environmental Quality

• Land degradation
• Accelerated eutrophication

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Land Degradation

• Undisturbed natural ecosystem in these regions usually

contain enough phosphorus in the biomass and soil

• rganic matter to maintain a substantial standing crop of

trees or grasses.

• Most of the phosphorus taken up by the plants is that

released from the decomposing residues of other plants. Very little is lost as long as the system remains undisturbed.

• Once the land is cleared for agricultural use, the losses of

phosphorus in eroded soil particles, in runoff water, and in biomass removals can be substantial. With in just a few years the system may lose most of the phosphorus that had cycled between the plants and the soils.

9

Land Degradation

• The remaining inorganic phosphorus in the soil is largely

unavailable for plant uptake. In this manner, the phosphorus-supplying capacity of the disturbed soil rapidly becomes so low that regrowth of natural vegetation is sparse and, on land cleared for agricultural use, crops soon fail to produces useful yields.

• Leguminous plants that might be expected to replenish

soil nitrogen supplies are particularly hard hit by phosphorus deficiency, because low phosphorus supply inhibits effective nodulation and retards the biological N- fixation process. (補充)

10

Water Quality Degradation

• Point sources, such as sewage treatment plant
• utflows, industries, and the like, are relatively

easy to identify, regulate, and clean up.

• Nonpoint sources of P are principally runoff

water and eroded sediments from soils scattered throughout the affected watershed.

11

Phosphorus Losses in Runoff

• Particulate P
• Dissolved P

乳牛場 廣義的豬

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Delaware Netherlands

磷施用過量

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Precipitation

Phosphorus balance in surface soil (Utisoils) of adjacent and agricultural watersheds

已農耕>100年 未被干擾>40年

自從被耕犛起，農地已 有近一半的有機磷被轉 變為無機磷或流失，其 礦化作用是林地的4倍， 因逕流流失的則達8倍。

Particulate form 佔 95% 95% Particulate form 5% Particulate form 含磷的砂塵 14

Phosphorus Losses in Runoff

耕犛會增加 particulate P 的流失，但不耕犛會讓 dissolved P (通 常來自化學肥或糞肥) 較易流失，因此耕犛翻土可讓 dissolved P 被吸附而較不易流失。

圓盤犁 15

pfiesteria

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Management of phosphorus

18

The Phosphorus Cycle

• HPO4

2-, H2PO4

• 19

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The Phosphorus Cycle

• Organic phosphorus
• Calcium-bound inorganic phosphorus
• Iron- or aluminum-bound inorganic phosphorus
• Phosphorus is not generally lost from the soil in gaseous

form.

• Because soluble inorganic form of phosphorus are

strongly adsorbed by mineral surfaces, leaching losses of inorganic phosphorus are generally very low.

• The amount of P that enters the soil from the atmosphere

(sorbed on dust particles) is quite small (0.05 to 0.5 kg/ha annually), but may nearly balance the losses from the soil in undisturbed forest and grassland ecosystem.

22

Organic Phosphorus in Soils

• Inositol phosphorus or phosphorus esters of a sugarlike
• compound. 肌醇 C6H6(OH)6
• Nucleic acids
• Phospholipids
• Dissolved organic phosphorus (DOP)

23

Organic Phosphorus in Soils

• Inositol phosphorus are the most abundant of the known
• rganic P compounds, making up 10 to 50% of the total
• rganic P. They interact with the higher-molecular-weight

humic compounds.

• Nucleic acids are adsorbed by humic compounds as well

as silicate clays. Adsorption on these soil colloids probably helps protect the phosphorus in nucleic acids from microbial attack.

• The nucleic acids and phospholipids together probably

make up only 1 to 2% of the organic P in most soils.

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Organic Phosphorus in Soils

• The other chemical compounds that contain most of the

soil organic P have not yet been identified, but much of the organic P appears to be associated with the fulvic acid.

• Dissolved organic phosphorus (DOP) is generally more

mobile than soluble inorganic P, probably because it is not so readily adsorbed by organic clays and by CaCO3 layers in the soil. In the lower horizons of such soils, the DOP commonly makes up more than 50% of the total soil solution P.

• In heavily manured areas with sandy soils DOP can leach

down to nearly 2 m.

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Organic Phosphorus in Soils

• The relative amounts in the two forms vary greatly

from soil to soil. The organic fraction generally constitutes 20 to 80% of the total phosphorus in surface soil horizons.

• The deeper horizons may hold large amounts of

inorganic phosphorus, especially in soils from arid and semiarid regions.

26 27

Calcium phosphate compounds Calcium phosphate compounds Adsorption by iron and aluminum oxides

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Organic Phosphorus in Soils

土壤無法完全吸收過多的 有機磷

42 years Cow manure

僅有機磷可穿透至 1.0 m 以下

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Mineralization of Organic P

• Net immobilization of soluble P is most likely to occure if

residues added to the soil have a C/P ratio greater than 300:1, while net mineralization is likely if the ratio is below 200:1.

30

Mineralization of Organic P

• In temperate regions, mineralization of organic P in soils

typically releases 5 to 20 kg P/ha/yr, most of which is readily adsorbed by growing plants. These values can be compared to the annual uptake of P by most crops, trees, and grasses, which generally ranges from 5 to 30 kg P/ha.

• When forested soil are first brought under cultivation in

tropical climates, the amount of P released by mineralization may exceed 50 kg/ha/yr, but unless P is added from outside sources these high rates of mineralization will soon decline due to the depletion of readily decomposable soil organic matter.

31

Contribution of Organic P to Plant Needs

• Recent evidence indicates that the readily decomposable
• f easily soluble fractions of soil organic phosphorus are
• ften the most important factor in supplying P to plants in

highly weathered soils (e.g., Ultisols and Oxisols), even though the total organic matter content of these soils may not be especially high.

• The inorganic P in the highly weathered soils is far too

insoluble to contribute much to plant nutrition.

• Apparently plant roots and mycorrhizal hyphae are able to
• btain some of the P released from organic forms before it

forms inorganic compounds that quickly become insoluble.

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Contribution of Organic P to Plant Needs

• In contrast, it appears that the more soluble inorganic

forms of P play the biggest role in P fertility of less weathered soils (e.g., Mollisols and Vertisols), even though these generally contain relatively high amounts of soil organic matter.

33

Phosphorus Removal from Wastewater

Environmental soil scientists and engineering remove phosphorus from municipal wastes by taking advantage of some

• f the same reactions that bind phosphorus in soils. After

primary and secondary sewage treatment that removes solids and oxidizes most of the organic matter, tertiary treatment in huge, specially designed tanks causes phosphorus to precipitate through reaction with iron and aluminum compounds, such as the following: Al2(SO4)3∙14H2O + 2PO4

3‐  2AlPO4 + 3SO4 2‐ + 14H2O

FeCl3 + PO4

3‐  FePO4 + 3Cl‐

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Phosphorus Removal from Wastewater

• Other less‐expensive tertiary treatment approaches involve

the spraying of the wastewater on vegetated soils. Natural and plant process clean the phosphorus and other constituents out of the waste water.

• In some infiltration systems, the water percolates through

relatively permeable soils.

• Other system, termed overland flow systems, use finer‐

textured, less‐permeable soils, over which water slowly flows, permitting the upper few centimeters of soil and the vegetation to remove most of the soluble phosphorus and

• ther contaminants.
• 大漢溪人工濕地之自然淨水系統

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Inorganic Phosphorus in soils

• Phosphorus fixation
• Phosphorus retention is a some what more general term

that includes both precipitation and fixation reactions.

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Inorganic Phosphorus Compounds

最難溶

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紅磷鐵礦 磷鋁石

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Inorganic Phosphorus Compounds

• The apatite minerals are the least soluble, while the

simpler mono- and dicalcium phosphates are readily available for plant uptake. (磷灰石)

• Strengite and variscite have very low solubilities in

strongly acid soils and become more soluble as soil pH rises.

41

Effect of Aging on Inorganic Phosphate Availability

42

Solubility of Inorganic Phosphorus in Acid Soils

• At moderate pH values, adsorption on the edges of

kaolinite or on the iron oxide coating on kaolinite clays plays an important role.

43

Precipitation by Fe, Al, and Mn Ions

• Probably the easiest type of P-fixation to visualization is

the simple reaction of H2PO4

• ions with dissolved Fe3+,

Al3+, and Mn2+ ions to form insoluble hydroxy phosphate

• precipitates. (形象)
• In strongly acid soils, enough soluble Al, Fe, or Mn is

usually present to cause the chemical precipitation of nearly all dissolved H2PO4

• ions by reactions such as the

following:

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Precipitation by Fe, Al, and Mn Ions

• Freshly precipitated hydroxy phosphates are slightly

soluble because they have a great deal of surface area exposed to the soil solution. Therefore, the P contained in them is, initially at least, somewhat available to plants.

• Over time, however, as the precipitated hydroxy

phosphates age, they become less soluble and the P in them becomes almost completely unavailable to most plants.

45

OH- MoO42- Organic acids Kaolinite

46

Figure 14.15

Reaction with Hydrous Oxides and Silicate Clays

• Availability of such adsorbed H2PO4
• may be increases by

(1) liming the soil to increase the hydroxy ions, or (2) adding organic matter to increase organic acids (anions) capable of replacing H2PO4

• . (Figure 14.15b)
• With this step (Figure 14.15d), the phosphate becomes an

integral part of the oxide mineral and the likelihood of its release back to the soil solution is extremely small. (可能 性)

• Finally, as more time passes, the precipitation of

additional Fe or Al hydrous oxide may bury the phosphate deep inside the oxide particle.

47

Effect of Iron Reduction Under Wet Conditions

• Prolonged anaerobic conditions can reduce the iron in

these complexes from Fe3+ to Fe2+, making the iron- phosphate complex much more soluble and causing it to releasing P into solution. (拉長)

• The release of P from iron phosphates by means of the

reduction and subsequent solubilization of iron improves the P availability in soils used for paddy rice.

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2018/5/29 13 Effect of Iron Reduction Under Wet Conditions

• Phosphorus bound to soil particles may accumulate in

river- and lake-bottom sediments, along with organic matter and other debris. As the sediments become anoxic, the reducing environment may cause the gradual release

• f P held by hydrous iron oxides.
• The P erodes from soils today may aggravate the problem
• f eutrophication for years to come, even after the erosion

and loss of P from the land has brought under control. (加 劇)

49

Inorganic Phosphorus Availability at High pH Values

50 51

Ca(H2PO4)2· H2O + H2O CaHPO4· 2H2O + H3PO4

產生的含 H3PO4 溶液(pH=1.4)向外圈流動， 並溶解了大量的 Fe、Al、Mn。 磷和 Fe、Al、Mn 快速反應

Inorganic Phosphorus Availability at High pH Values

• Reversion of soluble fertilizer P to extremely insoluble

calcium phosphate form is most serious in the calcareous soil of low-rainfall regions.

• Fe and Al impurities in calcite particles may also adsorb

considerable amounts of phosphate in these soil.

• The activity of fungi in releasing organic acids such as

citric acid solubilizes the highly insoluble phosphates making them available for absorption first by the fungi and ultimately by higher plants.

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Phosphorus‐Fixation Capacity of Soils

• Figure 14.18: phosphorus fixation (next

slide)

54 55

Part (c) illustrates how organic anions, larger organic molecules, and certain strongly fixed inorganic anions can reduce the sites available for fixing phosphorus.

Phosphorus‐Fixation Capacity of Soils

I Q PBC   

Potential buffering capacity

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Phosphorus‐Fixation Capacity of Soils

• Equilibrium phosphorus concentration (EPC)
• The solution concentration (x-axis) at which zero fixation
• ccurs (P is neither released nor retained) is called the
• EPC0. The EPC0 is an important soil parameter because it

indicated both the level of P fertility and the hazard of P loss by solution in runoff water.

• 土壤中若所有位址都固定了磷，則多餘的磷無法被固

定或已被固定的磷遇水則產生脫附，此時稱為磷的零 固點。

57

Factors Affecting the Extent of P Fixation in Soils

• Soils that remove more than 350 mg P/kg of soil from

solution are generally considered to be high phosphorus-fixing soils.

• High phosphorus-fixing soils tend to maintain low

phosphorus concentrations in the soil solution and in runoff water.

58

Amount of Clay Present

• Most of the compounds with which P reacts are in the

finer soil fractions.

• If soils with similar pH values and mineralogy are

compared, P fixation tends to be more pronounced and ease of P release tends to be lowest in those soils with higher clay contents.

59

Types of Clay Minerals Present

• Generally, those clays that possess greater anion

exchange capacity (due to positive surface charge) have a greater affinity for phosphate ions.

• Extremely high P fixation is characteristic of

allophane clays typically found in Andisols and other soils associated with volcanic ash.

• Gibbsite and goethite also strongly attract and hold

phosphorus ions.

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Types of Clay Minerals Present

2:1 clays « 1:1clays ＜carbonate crystals ＜crystalline Al, Fe, Mn oxides ＜amorphous Al, Fe, Mn oxides, allophane

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Types of Clay Minerals Present

62

Effect of Soil pH

• As a general rule in mineral soils, phosphate fixation

is at its lowest (and plant availability is highest) when soil pH is maintained in the 6.0 to 7.0 range.

• Even of pH ranges from 6.0 to 7.0, phosphate

availability may still be very low, and added soluble phosphates will be readily fixed by soils. The low recovery by plant of phosphates added to field mineral soils in a given season is partially due to this fixation.

63

Effect of Organic Matter

• Organic matter generally has little capacity to strongly fix

phosphate ions. Soil high in organic matter, especially active fractions of organic matter, generally exhibit relatively low levels of P fixation.

• First, large humic molecules can adhere to the surfaces of

clays and metal hydrous oxide particles, masking the P- fixation sites and preventing them from interacting with P ions in solution.

• Second, organic acids produced by plant roots and microbial

decay can serve as organic anions, which are attracted to positive charges and hydroxyls on the surfaces of clays and hydrous oxides.

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Effect of Organic Matter

• Third, certain organic anions and similar compounds can

entrap reactive Al and Fe in stable organic complexes call

• chelates. Once chelated, these metals are unavailable for

reaction with P ions in solution.

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Effect of Organic Matter

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Practical Control of Phosphorus in Soils

1. Patterning fertilizer rates to fit soil phosphorus status 2. Placement of phosphorus 3. Combination of ammonium and phosphorus fertilizers 4. Cycling of organic matter 5. Control of soil pH 6. Enhancement of mycorrhizal symbiosis 7. Choice of phosphorus-efficient plants 8. Reduction of runoff and sediment losses, especially from fertilized and manured land 9. Capturing excess phosphorus before it enters mainstream channels

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Practical Control of Phosphorus in Soils

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Practical Control of Phosphorus in Soils

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The NH4

+ ions likely resulted in increased acidity near the roots

and solubilized some of the soil phosphorus, which was then taken up by the ryegrass plants, leaving a lower P level in the soil.

Practical Control of Phosphorus in Soils

樹薯 高粱 甘藍菜

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Practical Control of Phosphorus in Soils

Tithonia 植物殘體加入能增加磷的有效性

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Practical Control of Phosphorus in Soils

Al2(SO4)3 chicken litter poultry houses

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Diagram showing the annual inputs and outputs of phosphorus for the State of Illinois, averaged. The Potassium Cycle

74

改善

(Red pine trees)

75

重新植林

In A horizon

The Potassium Problem in Soil Fertility

1. Availability of Potassium 2. Leaching Losses 3. Plant Uptake and Removal 4. Luxury Consumption

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Availability of Potassium

• The total quantity of this element is generally greater

than that of any other major nutrient element. Amounts as great as 30,000 to 50,000 kg potassium in the upper 15 cm of 1 ha of soil are not at all uncommon.

• Most of this element is held rigidly as part of the

primary minerals or is fixed in forms that are, at best,

• nly moderately available to plants.
• A very large proportion of N, P, and K in the soil is

insoluble and relatively unavailable to growing plants.

77

Leaching Losses

The fact that the K+ ions can more easily replace Ca2+ ions than they could replace Al3+ ions allows more of the K+ ions to be removed from solution by cation exchange in the limed soil. The removal of K+ ions from solution by adsorption on the colloids will reduce their loss by leaching, but they will still be at least moderately available for plant uptake.

78

Plant Uptake and Removal

• Plants take up very large amounts of potassium,
• ften five to ten times as much as for phosphorus

and about the same amounts as for nitrogen. If most

• r all of the above‐ground plant parts are removed in

harvest, the drain on the soil supply of potassium can be very large.

• A 60‐Mg/ha yield of corn silage may remove 160

kg/ha of potassium. (青貯飼料)

• Conventional bolewood timber harvest typically

removes about 100 kg/ha of potassium. (樹幹木材)

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Luxury Consumption

The tendency of plants to take up soluble potassium far in excess of their needs if sufficiently large quantities are present. The tendency is termed luxury consumption, because the excess potassium absorbed does not increase crop yields to any extent.

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Luxury Consumption

• If plant residues are not returned to the soil, the

removal of this excess potassium is decidedly wasteful.

• High levels of potassium may depress calcium uptake

and cause nutritional imbalances both in the plants and in animals that consume them.

81

Forms and Availability of Potassium in Soil

1. K in primary mineral structure: unavailable 2. Nonexchangeable K in secondary minerals: slow available 3. Exchangeable K on soil colloids: readily available 4. K soluble in water: readily available The ability to obtain potassium held in the slowly available forms differs greatly among plant species. Many grass plants with fine, fibrous root systems are able to exploit potassium held in clay interlayers and near the edges of mica and feldspar crystals of clay and silt size. Elephant grass have been shown to obtain potassium from even sand-sized primary minerals, a form of potassium usually considered to be unavailable.

82

Forms and Availability of Potassium in Soil

Only 1 to 2% of the totals soil potassium is really available. Available potassium exists in soils in two forms: (1) in the soil solution, and (2) exchangeable potassium adsorbed on the soil colloidal surface.

83

The dehydrated K ion is much smaller than the hydrated ions of Na+, Ca2+, Mg2+,

• etc. When K is added to a soil containing 2:1-type minerals such as vermiculite, the

reaction may go to the left and K ions will be tightly held (fixed) in between layers within the crystal, producing a fine-grained mica structure.

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Exchangeable and nonexchangeable K levels in a Ultisol in South Carolina after 30 years growth of a loblolly pine following 150 years of cultivated crops. Although the exchangeable K levels was quite low, tree growth was not adversely affected, and large quantities of this element were absorbed by the trees over the 30-year period. This was made possible by the conversion of nonexchangeable K to the exchangeable form, which was readily taken up by the trees. The upper horizons may have been depleted somewhat of nonexchangeable K, but the deep tree roots were able to use the K released from the nonexchangeable form in the lower horizons.

85

The data in Table 14.10 indicates the magnitude of the release of nonexchangeable K from certain soils. In these soils, the potassium removed by plants was supplied largely from nonexchangeable forms. Very sandy soils with low CEC are poorly buffered with respect to K. In them, the K ion concentration may be quite high at the beginning of a growing season

• r just after fertilization, but the soils have little capacity to maintain the K

concentration, as plants remove the dissolved K from the soil solution during the growing season.

86

Factors Affecting Potassium Fixation in Soils

1. The nature of the soil colloids 2. Wetting and drying (mechanism is not well understood) 3. Freezing and thawing (mechanism is not well understood)( 融化) 4. The presence of excess lime

87

Factors Affecting Potassium Fixation in Soils

• Kaolinite and other 1:1- type clays fix little K.
• Clays of the 2:1 type, such as vermiculite, fine-grained

mica, and smectite fix K very readily and in large quantities.

• The K+ and ammonium ions are attracted between layers

in the negatively charged clay crystals. Vermiculite has a greater fixing capacity than montmorillonite.

• In strongly acid soils the tightly held H+ and hydroxyl

aluminum ions prevent the K+ ions from being closely associated with the colloidal surface, which reduces their susceptibility to fixation.

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Factors Affecting Potassium Fixation in Soils

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Figure 14.35 The effect of pH on the fixation of potassium soils in indis

Practical Aspects of Potassium Management

• Excessive levels of K that depress Ca and Mg in the

forage must be avoided to maintain plant and animal

• health. (草料,飼料)
• Soils of arid regions are often well supplied with

weatherable K-containing minerals and can therefore supply adequate K for many years, even under irrigation where leaching is more important and plant removal is

• great. However, continued crop removal can deplete the

available K pools even in these soils.

91 92