『Abstract
Cultivated soils in the Everglades are being converted to their
historic use as pastures or seasonally flooded prairies as pars
of restoration efforts, but long-term cultivation may have altered
soil P distribution and availability which may pose eutrophication
hazards upon change in land use. The objectives of this study
were to determine the distribution of P in soil chemical and physical
fractions for contrasting long-term land management practices.
The distribution of P in labile, Fe-Al bound, Ca bound, humic-fulvic
acid, and residual pools in five aggregate-size fractions were
measured for fields under sugarcane (Saccharum sp.) cropping
for 50 years and perennial pasture for 100 years. Both land uses
were characterized by a high degree of macro aggregation, as aggregates
>0.25 mm contained 76 and 83% of the total soil under cultivation
and pasture, respectively. Soils under sugarcane sequestered a
total of 77 kg ha-1 more P than pasture at 0-15 cm.
The distribution of P in chemical fractions significantly varied
between land uses as cultivation increased P sequestration in
Ca-bound fractions more for sugarcane (244 kg P ha-1)
than pasture (65 kg P ha-1). Pasture sequestered more
P in organic pools, as storage in humic-fulvic acid and residual
fractions were 26 and 25%, respectively, higher than sugarcane.
Labile P was 100% higher for pasture than sugarcane, but Fe-Al
bound P storage did not differ between land uses. Aggregation
increased P sequestration in humic-fulvic acid and residual fractions,
and P storage in organic pools increased with increasing aggregate
size. In contrast, cultivation decreased aggregation and increased
P accumulation in inorganic fractions. Long-term cultivation altered
the distribution of soil P from organic to inorganic pools. The
P stored in organic pools is stable under current land use, but
may be unstable and pose eutrophication hazards upon onset of
future land use change to the seasonally flooded prairie ecosystem.
Keywords: Aggregates; Everglades; Histosol; Land use; Phosphorus
fractionation』
1. Introduction
2. Materials and methods
2.1. Site description
2.2. Soil sampling and analysis
3. Results and discussion
3.1. Soil characterization
3.2. Soil aggregate-size distribution
3.3. Phosphorus fractions in whole soil
3.4. Soil P fractions within aggregate-size classes
3.4.1. Labile P
3.4.2. Fe-Al bound P
3.4.3. Ca-bound P
3.4.4. Humic-fulvic acid P
4. Conclusions
References
※リンの連続分別法は、Qualls and Richardson(1995)とIvanoff et al.(1998)とReddy et al.(1998)による。