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phosphorus availability to water from animal manures and manure ...

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phosphorus availability to water from animal manures and manure ...

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    1: Phosphorus Availability to Water from Animal Manures and Manure-Amended Soil Leslie Cooperband Laura Ward Good Department of Soil Science University of Wisconsin-Madison

    Slide 3:Make sure I discuss the concept of soil solution P being in equilibrium with these other P pools. As solution P is depleted, it drives dissolution or desorption or mineralization processes to occur.Make sure I discuss the concept of soil solution P being in equilibrium with these other P pools. As solution P is depleted, it drives dissolution or desorption or mineralization processes to occur.

    7: Factors controlling organic P mineralization C:P ratio of organic residues; >300:1; <200:1 Soil temperature Soil moisture Soil texture Tillage

    8: Solubility of P minerals Calcium phosphates (apatites) insoluble at high pH values (>7.5). Iron (strengite) and aluminum (variscite) phosphates insoluble at low pH values (<5.5).

    15: Factors affecting P retention in soils Soil clay content and presence of iron and aluminum oxides Clay mineralogy (variable charge vs. permanent charge) Soil pH (P retention is lowest at pH 6-7) Organic matter

    16: Effects of organic matter Humic substances adhere to clay and metal hydroxide surfaces blocking P retention sites Plant roots and decomposing OM produce organic acids (negatively charged) that compete with phosphate anions for retention sites Organic acids chelate free Al, Fe, Ca making them unavailable for precipitation with soluble phosphate anions

    17: Clarification of soil P retention Precipitation reactions of P with cations like Al, Fe and Ca; form secondary minerals. These mineral precipitates have varying solubilities depending on their crystallinity and the degree of “substitution.” (e.g., Mg, Si, Mn, NH4) P can be retained in an exchangeable form when it is sorbed to soil clays or metal oxides. When sorption sites are saturated, more P is in soil solution

    18: Manure P forms

    19: P forms in animal manures: organic, slow release fertilizer concept “P in organic material is mainly in the organic fraction..” (Lemunyon and Gilbert, 1993) 70-90% of ingested P is excreted AND Organic fraction of P in manures can be as much as 66% (Mikkelsen and Gilliam, 1995) P forms determined by sequential chemical extractions; forms operationally defined

    20: Manure P forms: Equal to soluble fertilizers concept Some fertilizer comparison trials show manure P availability less than superphosphate (at same TP application rate) Others show manure P availability equal to or greater than fertilizer P

    21: P in manure amended soils

    22: Clarification of terms Available P Implies availability for plant uptake Water soluble P Implies susceptibility to loss in runoff

    23: Robinson et al. (1995) study of long-term manure applications to soils Relative availabilities of P forms in soils amended with beef, poultry litter, swine manure Large increases in inorganic soil P fractions relative to organic P fractions Greatest increase was in Ca-phosphates even with soil pH values 5.9-7.2; attributed to Ca added with manures No distinction among manures

    24: What happens to soil P in excessively fertilized soils? Pierzynski et al. (1990) found discrete P rich particles containing Al, Si, K, Ca and Fe; pH independent Ca-P dominant particles were minor component of P rich particles identified Could NOT find discrete, well crystallized P minerals Contradicted theory that P added to soils precipitates as secondary phosphate minerals that ultimately control P solubility

    25: Effect of organic acids and trace metals Humic and fulvic acids inhibit formation of Ca phosphate solids Heavily manured soils contain high concentrations of organic acids, Si, Fe, Mg Supersaturated with respect to soluble P (Harris et al. 1994) Mayer and Jarrell (1995) study of stream sediments associated with high P soils showed presence of colloidal Fe-P solids; formed when Fe2+ oxidized to Fe3+

    26: Studies suggest that heavily fertilized soils don’t follow the “rules” related to P mineral precipitation and P retention.

    Slide 31:The threshold concept completely contradicts the concept that manure P and STP are additive. It also shows no values on the Y-axis.The threshold concept completely contradicts the concept that manure P and STP are additive. It also shows no values on the Y-axis.

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