『Abstract
We investigated the effects on phosphorus (P) release of the
addition of potato, wheat, and sunflower residues and fruit compost
to five calcareous soils. Residue was added at the rate of 20
g kg-1. After 2 months of incubation, P values in control
and amended soils were used for kinetic studies and fractionated
by a sequential extraction procedure. The relative contribution
of available P fraction (KCl-P) increased from 1.4％ in control
soils to to 1.8％, 1.9％, 2.2％, and 2.3％ in soils amended by fruit,
wheat, potato, and sunflower residue addition, respectively, indicating
that organic residues increased P in this fraction. In soils amended
with different residues, the percentage of Olsen-P released over
86-h successive extractions with 0.01 M CaCl2
ranged from 57.6％ for fruit residue addition (average of five
soils) to 60.5％ for potato residue addition. The ability of residues
to release P depended on the soil properties, with 21.9 mg kg-1
(average of all residues) released to soil 2 and 77.4 mg kg-1
released to soil 4. Also residues behaved differently, with 31.5
mg kg-1 (average of five soils ) released by fruit
residues and 40.0 mg kg-1 released by sunflower residues.
Release of P was best described by a parabolic diffusion model.
The corresponding rate constant (mg kg-1 h-1/2
for P release for amended soils, defined as the release rate averaged
for five soils, was found to decrease in the order: potato (2.73)＞sunflower
(2.61)＞wheat (2.56)＞fruit (2.50). The present study demonstrates
the addition of residues improves P availability of these calcareous
soils by increasing extractable P and the release rate and could
be an alternative, indigenous source of P. However, the increase
in P availability and the release rate following organic residue
application suggests high potential mobility to water sources.
Keywords: Phosphorus; Kinetics; Calcareous soils; Plant residues』
Introduction
Materials and methods
Experimental soils
Organic residues
Sequential extractions of P
Kinetics of phosphorous release
Results and discussion
Soil and plant residue properties
Phosphorus fractions in soils
Kinetics of P release
Kinetics model
Conclusions
References