Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/20/2002
Publication Date: N/A
Interpretive Summary: The amount of phosphorus available from animal manures is variable and not well understood. We conducted this research to see how fertilizer and manure phosphorus change the amount of phosphorus available in the soil. After incorporating different phosphorus sources (fertilizer, beef, dairy, poultry, or swine manure) in the soil, the amount of applied phosphorus that can be used rapidly by plants decreases very quickly, regardless of the source. This is due to the formation of phosphorus-aluminum compounds that plants can not use. The amount of phosphorus extracted with different soil tests is directly related to the amount applied. Rapidly available phosphorus is increased more by fertilizer than by manure, but the opposite may be true for more slowly available phosphorus pools in the soil. The amount of phosphorus present in the soil before applying manure or fertilizer also has an effect; phosphorus levels increase more quickly if high levels already exist in the soil. This research can help scientists and nutrient managers recognize the differences between nutrient sources, and identify optimal soil phosphorus levels.
Technical Abstract: Manure and fertilizer phosphorus (P) sources vary in their contributions to soil P pools. We conducted incubation experiments to (1) assess temporal changes in soil P concentration for 84 d following application of fertilizer or manure (beef, dairy, poultry, or swine), and (2) evaluate interactive effects of P rate, P source and background P level on soil P pools. Changes in soil P over time were monitored following amendment (100 mg total P kg-1) of a sandy loam soil (pH 5.8). Water soluble P (WSP), CaCl2-extractable P (CaCl2-P), and modified Morgan P (MMP) declined to less than 2 mg P kg-1 soil within 21 d of application; P extracted by anion exchange membrane (AEMP) and Mehlich-III (M3P) also declined rapidly and are attributed to the high level of exchangeable aluminum (Al) and iron (Fe) in this soil. Ninety (90) d after application, all soil P pools exhibited linear increases in concentration, regardless of P source. Fertilizer P was more efficient at increasing CaCl2-P and M3P. Manure P sources generally had a greater effect on MMP, where poultry manure was more efficient than all other sources. Efficiency of P sources at increasing soil P concentration (b, slope of linear regression) varied from less than 1% for rapidly available P pools (CaCl2-P) to nearly 50% for more recalcitrant P (M3P). The amount of soluble P increased rapidly when soil P saturation exceeded 25%. Manure and fertilizer P contribute to different soil P pools, and these differences are magnified at high application rates and high background soil P levels.