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The understanding of P sorption and desorption by soils is impor-The relationships between P-sorption capacity, P tant for safeguarding water quality and for fertilizer management. availability and soil components in calcareous soils have Little is known about the P-sorption characteristics of the calcareous been studied in other states and countries. Ryan et al. soils and limestone bedrocks in southern Florida. In this study, 19 samples of calcareous soil and subsurface limestone bedrock were (1985) reported that P sorption in soils is related more collected from the southern Everglades wetland, pineland, and nearby to their Fe oxide than CaCO 3 content. Solis and Torrent farmland. At very low P concentrations, P sorption in these soils fit (1989) found P-sorption capacity of soil to be highly the linear isotherm. The equilibrium P concentration at zero-net P correlated with Fe oxide and clay content, and that sorption (EPCo) of soils correlated positively with P saturation. Phos-CaCO 3 plays a less important role in P sorption. Howphorus-sorption data of soils at medium P concentrations fit the ever, Sharpley and Smith(1985) observed that concen-Freundlich and Langmuir equations up to a point at high P concentratrations of labile P in calcareous soils after fertilizer tions where the slope of the isotherm changed abruptly. In bedrock applications are negatively correlated to CaCO 3 content. samples the sorption-isotherm-inflection point, which is caused by P Afif et al. (1993) also reported that the ratio of Olsen-P precipitation, occurred at much lower solution P concentrations than to applied P is negatively correlated to Fe oxides content in the case of soils (4-18 vs. 400-600 mg mL Ϫ1). Also bedrock samples at low P application rates and to CaCO 3 content at had significantly lower Freundlich values, K f , than soils. The sorption of P in soils occurred at relatively low solution P concentrations (as high P application rates. Most previous studies involved indicated by Freundlich value, K f), and appears to be caused by strong agricultural soils with active CaCO 3 content of Ͻ300 g affinity of the noncarbonate clay, while the P sorption at relatively high kg Ϫ1 (Holford and Mattingly, 1974, 1975a). Thus the solution concentrations (as indicted by Langmuir maximum sorption, P chemistry in nonagricultural soils or agricultural soils S max) appears to be caused by the affinities of both the noncarbonate with CaCO 3 contents as high as 928 g kg Ϫ1 has not clay and carbonate clay. Phosphorus-sorption values (P sorption) estibeen elucidated clearly. Calcareous soils often contain mated from the one-point isotherm were comparable with the S max limestone fragments or lie directly upon limestone bedvalues calculated from the Langmuir isotherm. Phosphorus saturarock. Holford and Mattingly (1975b) measured the tion and the P-retention capacities (S max or P sorption) were correlated P-sorption capacity of ground limestone. Since the strongly to the percentage of P desorption. P-sorption capacity of carbonate depends ...

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In this paper, we synthesized a biobased polyurethane using liquefied corn stover, isocyanate, and diethylenetriamine. The synthesized polyurethane was used as a coating material to control nitrogen (N) release from polymer-coated urea. A novel superabsorbent composite was also formulated from chicken feather protein (CFP), acrylic acid, and N,N'-methylenebisacrylamide and used as an outer coating material for water retention. We studied the N release characteristics and water-retention capability of the double-layer polymer-coated urea (DPCU) applied in both water and soils. The ear yields, dry matter accumulation, total N use efficiency and N leaching from a sweet corn soil-plant system under two different irrigation regimes were also investigated. Comparison of DPCU treatments with conventional urea fertilizer revealed that DPCU treatments reduced the N release rate and improved water retention capability. Evaluation of soil and plant characteristics within the soil-plant system revealed that DPCU application effectively reduced N leaching loss, improved total N use efficiency, and increased soil water retention capability.

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