『Abstract
Rate of phosphorus (P) transformation in soils can significantly
influence P fertility of soils. The transformation rate and fractionations
of P in 20 calcareous soils of varying properties were investigated.
Phosphorus was added to the samples at rates of 200 mg kg-1
soil. The samples were incubated for 3, 24, 168, 336, 504, 720,
1440, and 2160 h at 25℃ and Olsen-P was determined after each
incubation period. The P release in the studied soils was initially
rapid followed by a slower release that lasted up to 2160 h. The
transformation rate of Olsen-P for soils was estimated by best
fitted kinetic equation (parabolic) for above incubation periods.
There were differences in the rates at which redistribution took
place between soils and P. Phosphorus in control and amended soils
were fractionated before and after 2160 h incubation by sequential
extraction procedure, in which the P fractions were experimentally
defined as exchangeable (KCl-P), Fe- and Al-bound (NaOH-P), Ca-bound
(HCl-P, and residual P (Res-P) fractions. The results showed a
sharp decrease in Olsen-P within 3 h after P addition. Relative
NaOH-P in amended soils ranged from 6.6 to 13.5％. Relative HCl-P,
Res-P and KCl-P ranged from 49.9 to 71.2, 13.5 to 26.7, and 7.4
to 13.3％, respectively. There were changes in the proportional
distribution of P in all the soils during 2160 h of incubation
with amended P. In general the proportions of P associated with
the most weakly bound fraction (KCl-P) tended to decrease, with
corresponding increases in the NaOH-P and HCl-P fractions during
the incubation. The principal component analysis showed that the
first four components explained 77.1％ of the overall variation.
Keywords: Phosphorus; Calcareous soil; Kinetics; Fractionation;
P transformation rate』
1. Introduction
2. Materials and methods
2.1. Physico-chemical properties of soils
2.2. Incubation study
2.3. Sequential extractions of P
2.4. Statistical analysis
3. Results and discussion
3.1. Soils
3.2. Phosphorus release
3.3. Phosphorus release rate
3.4. Phosphorus fractions in soils
3.5. Correlations between P fractions with soil properties
3.6. Principal component analysis
4. Conclusions
References