『Abstract
Phosphogypsum (PG), a by-product of the P industries, has been
widely applied as an amendment to reduce Na saturation in soils.
However, some concern arise due to its content of some metals
and radionuclides. Thus, it is necessary to optimize the PG rates
to avoid excessive accumulation of such pollutants in soil. To
evaluate the effects of PG on drain flow and on the displacement
of Na by Ca in soils, a three-year field experiments wad conducted
in a commercial farm located in a reclaimed marsh area from SW
Spain. It involved two treatments (control - without PG - and
25 Mg ha-1 of PG, applied in April 2003 and again in
September 2004), done in triplicate in 250× 20 m plots, following
a randomized block design. Drainage flows were monitored, and
drain-water samples were analyzed for Na and Ca concentrations.
The recorded hydrographs revealed unexpected high lateral flows
of water within these soils. No statistically significant differences
were found in drained volumes, nor in Na and Ca losses through
drainage, between both treatments in each of the three growing
seasons (Gossypium hirsutum L. in 2003 and 2005; Beta
vulgaris L. in 2003-2004). Losses of Na and Ca in each irrigation
event were linearly related to the drainage to irrigation volume
ratio (p＜0.001); Ca, however, showed significantly different slopes
for both treatments. Cation concentration, Na adsorption ratio
(SAR), and electrical conductivity (EC) in the saturation extract
of soil at different depths were significantly affected by PG
and by the oscillation of saline water table during the experiment.
The efficiency of PG in displacing Na by Ca was estimated to be
about 30％, with the PG-attributable changes in Ca and SAR also
appearing in deeper soil layers and in adjacent control plots.
Keywords: Phosphogypsum; Salinity; Sodicity; Soil amendment; Irrigation;
Tile drain』
1. Introduction
2. Materials and methods
2.1. Experimental site and experimental design
2.2. Soil and water analysis
2.3. Statistical analysis
3. Results and discussion
3.1. Water balance (irrigation and drainage)
3.2. Salt balance (irrigation and drainage)
3.3. Effect of phosphogypsum on the soil salinity
4. Conclusions
Acknowledgements
References