Gustavo Navarro, Alan Wright, Xing Wang
Everglades Research and Education Center
University of Florida
Belle Glade, FL, USA
The Everglades Agricultural Area (EAA) encompasses approximately 280000 hectares, extending from Lake Okeechobee south to the Broward County line. Most of the soils in this area are Histosols (soils that are composed mainly of organic materials). The principal crops are sugarcane and winter vegetables. Sod and rice are grown on a smaller scale, but sod production is gaining in importance (Snyder, 2005).
The organics soils of the Everglades Agricultural Area formed when the flooded conditions limited soil oxygen levels and organic matter production exceeded organic matter decomposition. Subsequently, drainage of the EAA was the leading cause of loss of the soil and a lowering of the surface elevation formerly known as subsidence. Furthermore, when these soils were drained, the rate of organic matter (OM) decomposition exceeded accumulation (Tate, 1980).
Drainage systems for agricultural practices and the use of P fertilizers for optimal crop production are common. Nonetheless, over-application of fertilizers contributed to excess P in run-off from the EAA into adjacent canals and wetlands. In addition, strategies for minimizing phosphorus inputs for crop production need to be developed.
Phosphorus adsorption in soils is highly dependant on pH and calcium carbonate levels. Moreover, increases in soil pH resulting from soil subsidence and incorporation of bedrock limestone into soil by tillage may have altered soil phosphorus dynamics and increased P fertilizer applications necessary to maintain crop yields.
2.1. Main objective.
The objectives of this study were to estimate potential effects of future subsidence and increasing soil Ca concentrations on soil P transformations and availability. Likewise, effects of calcium concentrations on soil microbial activity and organic matter decomposition rates will be assessed for different phosphorus applications rates.
2.2. Secondary objectives.
• Predict how soil subsidence and resulting changes in soils chemistry influence the behavior of phosphorus in soils.
• Develop statistical models.
3. Materials and methods
3.1. Site description
The samples were collected from 47-CD-105 from the Everglades Agricultural Research and Education Center (EREC). Four replicates were taken each called S1, S2, S3 and S4. Calcium carbonate was added to soil to simulate potential Ca levels in soils undergoing subsidence in the future. Soils were adjusted from their residual 2% Ca levels to levels of 5, 10, and 20%. This range encompasses current and future predicted soil Ca levels in the organic soils of the EAA. Of major concern is the fate of applied P fertilizers in subsiding soils of the EAA, and impacts of projected increases in soil CaCO3 levels of the fate of P fertilizes in soil. Soil P fertilizers were applied to Ca-amended soil at a wide range of P rates (0, 25, 100, 300 lb P2O5/ac) typical for crop production in the EAA. The fate of applied P into various P pools from labile to recalcitrant were followed up to 21 d after application. Moreover, plant-available P forms were measured during this time frame to determine how future subsidence impacts P availability to crops. Results of the study will be used to predict effects of calcification of soil on P availability to crops and to develop relevant P recommendations for the changing soils of the EAA.
3.2. Soil sampling
Samples were collected on January 22nd. Four different sites were sampled to 6 in. depth. Samples were stored in paper bags and dried at 70°C.
Sixty four samples were analyzed in order to determine water-holding capacity (WHC), bulk density (BD), Loss on...