Predicting Reduction in Phosphorus Storage Capacity over Time in Soils with Manure Additions.
ASA-CSSA-SSSA International Annual Meetings (November 12-16, 2006)
Phosphorus (P) concentrations in agricultural soils have substantially increased in the last decades, increasing the risks for surface and ground water contamination through P runoff and leaching. In sandy soils, the potential for P leaching is greater, especially in areas of intensive animal agriculture. The purpose of this study is to assess the reduction in P storage capa...
Phosphorus (P) concentrations in agricultural soils have substantially increased in the last decades, increasing the risks for surface and ground water contamination through P runoff and leaching. In sandy soils, the potential for P leaching is greater, especially in areas of intensive animal agriculture. The purpose of this study is to assess the reduction in P storage capacity at a site in the Suwannee River Basin (Florida and Georgia) receiving poultry manure additions. Four soil profiles in fields amended with poultry manure were sampled by horizon three times over 36 months. Initial P concentrations were low (less than 40 mg Mehlich 1-P kg-1). Approximately 82 mg P kg-1 were added to the soils between the first and the third sampling periods. Physical and chemical characteristics of the soils were determined, including water soluble P (WSP), oxalate extractable P, Al, Fe, and Mehlich 1-P. The P saturation ratio (PSR) was calculated as the molar ratio of oxalate extractable P to oxalate extractable Fe and Al. The soil P storage capacity (SPSC) was calculated for individual horizon and by profile, using a PSR threshold of 0.15. The SPSC refers to the amount of P that can be safely added to a certain volume or mass of soil before the soil becomes a P source. The analysis of the surface horizon of the profiles showed an average SPSC decrease from -23 mg P kg-1 to -54 mg P kg-1 after the third sampling. The results also showed average decreases in SPSC (31%) for the entire profile and corresponding average increases in WSP (131%) and Mehlich 1-P (180%) over the three-year period. SPSC can be used to predict site-specific safe P-loading for sandy soils.
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ASA-CSSA-SSSA International Annual Meetings (November 6-10, 2005)
Soil Carbon Pools in Slash Pine-Based Silvopastoral Systems of North Florida.
ASA-CSSA-SSSA International Annual Meetings (November 6-10, 2005)
Tree-based land-use systems such as agroforestry are expected to have better carbon (C) sequestration potential than most agricultural systems. Silvopastoral systems that integrate trees into animal production systems are the most widely practiced form of agroforestry in North America. C sequestration potential of such silvopastoral systems, especially the stable C pool in the soil, have, how...
Tree-based land-use systems such as agroforestry are expected to have better carbon (C) sequestration potential than most agricultural systems. Silvopastoral systems that integrate trees into animal production systems are the most widely practiced form of agroforestry in North America. C sequestration potential of such silvopastoral systems, especially the stable C pool in the soil, have, however, not been studied. We hypothesize that silvopastoral systems will have more stable (recalcitrant) C fraction in soil than under tree-less pasture under similar ecological settings. Soil C pools were examined in four farms of slash pine (Pinus elliottii) + bahia grass (Paspalum notatum) silvopastural systems in two soil types (Spodosol and Ultisol) in northern Florida. The specific objectives are to compare the distribution of labile and recalcitrant forms of C among different soil fractions (sand, silt, and clay), at different depths in silvopasture, treeless-pasture, and local natural vegetation systems. Soil samples were drawn from positions between trees in a row (TS), on an alley in a silvopasture (AS), on treeless-pasture (TP) and on natural vegetation (NV) systems at six different soil depths (0 5, 5 15, 15 30, 30 50, 50 75, and 75 125 cm). Plots at each site had similar management history, and by assumption, similar soil C levels prior to introducing silvopasture. Soils will be fractionated into sand, silt, and clay and the labile and recalcitrant forms of soil C in each fraction determined. The results will be used to evaluate the influence of slash-pine-based silvopastoral system on stable soil C, and thus C sequestration potential, in the two soil types. The work is in progress; results will be presented at the meeting.
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