Term
| Plant roots absorb phosphorus from... |
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Definition
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Term
| In general, roots absorb phosphorus in the form of... |
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Definition
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Term
| plants can also obtain certain forms of this phosphorous |
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Definition
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Term
| Phosphorus moves to the root surface through... |
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Definition
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Term
| this can reduce the movement of phosphorus from soil solution to roots |
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Definition
| Compaction of soils under agriculture fields |
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Term
| what Compaction of soils under agriculture fields can do to P in soil |
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Definition
| reduce the movement of phosphorus from soil solution to roots |
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Term
| what mycorrhizal fungi do for plants pertaining to P |
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Definition
| the presence of mycorrhizal fungi, which develop a symbiotic relationship with plant roots and extend threadlike hyphae into the soil, can enhance the uptake of phosphorus, as well especially in acidic soils that are low in phosphorus |
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Term
| P-sorption occurs when... |
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Definition
| the orthophosphates, H2PO4- and HPO42-, bind tightly to soil particles |
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Term
| Since phosphate is an anion, these particles will form strong bonds with phosphate. |
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Definition
| particles that generate an anion exchange capacity |
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Term
| some Particles with anion exchange capacity |
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Definition
-Aluminum and iron oxides
-Highly weathered kaolin clays (under acidic conditions)
-Amorphous materials. |
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Term
| where particles with anion exchange capacity are commonly found |
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Definition
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Term
| why P-sorption can become a major issue to achieve high crop yields |
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Definition
| because P-sorption results in a decrease of plant available phosphorus |
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Term
| Factors that affect P-sorption |
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Definition
-soil mineral type
-amount of clay
-pH
-temperature |
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Term
| how soil mineral type affects P-sorption |
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Definition
| Mineralogy of the soil has a great effect on P-sorption |
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Term
| the soils that tend to have the highest P-sorption and why |
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Definition
| o Volcanic soils tend to have the greatest P-sorption of all soils since volcanic soils contain large amounts of amorphous material. |
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Term
| why oxisols and ultisols have high P-adsorption capacities |
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Definition
| because of large amounts of aluminum and iron oxides and highly weathered kaolin clays |
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Term
| these soils have low P-sorption capacities |
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Definition
| less weathered soils and organic soils |
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Term
| how the amount of clay affects P-sorption and why |
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Definition
| As the amount of clay increases in the soil, the P-sorption capacity increases as well. This is because clay particles have a tremendous amount of surface area for which phosphate sorption can take place. |
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Term
| how pH affects P-sorption |
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Definition
| At low pH, soils have greater amounts of aluminum in the soil solution, which forms very strong bonds with phosphate. In fact, a soil binds twice the amount of phosphorus under acidic conditions, and these bonds are five times stronger. |
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Term
| how temperature affects P-sorption |
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Definition
| Generally, P-sorption increases as temperature increases. |
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Term
| Factors that decrease P-sorption |
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Definition
-Other anions, such as silicates, carbonates, sulfates, arsenate, and molybdate
-organic matter
-flooding |
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Term
| how Other anions, such as silicates, carbonates, sulfates, arsenate, and molybdate affect P-sorption |
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Definition
| They compete with phosphate for a position on the anion exchange site. As a result, these anions can cause the displacement, or desorption, of phosphate from the soil exchange site. Desorption causes phosphate availability in the soil solution to increase. |
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Term
| how organic matter increases P availability |
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Definition
-First, organic matter forms complexes with organic phosphate which increases phosphate uptake by plants.
-Second, organic anions can also displace sorbed phosphate.
-Third, humus coats aluminum and iron oxides, which reduces P sorption.
-Finally, organic matter is also a source of phosphorus through mineralization reactions. |
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Term
| how flooding affects P-sorption |
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Definition
| • Flooding the soil reduces P-sorption by increasing the solubility of phosphates that are bound to aluminum and iron oxides and amorphous minerals. |
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Term
| the 3 main mechanisms for phosphorus adsorption in soils |
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Definition
1: outer-sphere complexation
2: monodentate inner-sphere complexation
3: bidentate inner-sphere complexation |
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