C - Lublin

According to the data of Table 1, the chemical composition of HA and FA
varied considerably in the course of incubation. It is however seen that there is a
relationship between the contents of M and P in HA and FA. After incubation of P-
enriched soil for 3 years, the contents of M and P decreased considerably in HA but
increased in FA. Consequently, the P incorporation in humus molecules resulted in
the change of their reactivity in an acid medium. The P promoted reactions of M
elimination.
The reactivity of organic compounds is a function of the distribution of
electron density in their molecules. The UV-VIS absorption spectrum reveals the
excitability degree of molecular electron system. The variation of excitation state
from ground state may characterize energetic state of electrons belonging to
functional groups having double bonds.
The difference electronic spectra (Fig. 1) show the pronounced effect of P on
the electron energy state in the extractable HS. This fact suggests the P-induced
structural changes in humus molecules. Bathochromic band shift observed in the
region of 210-230 nm can be indicative of the appearance of additional C=C bonds
in the side chains of the P-modified molecules of HS. Another P-induced spectral
change is observed in the region of 250-350 nm (Fig. 1). This absorption band is
Fig. 1. Electronic spectra of alkali-soluble HS
and FA: 1 - initial soil; 2 – P-treated soil,
incubation for 7 days; 3 – incubation for 1
year; 4 – incubation for 3 years; 5 – FA from
initial soil; 6 – FA from P-treated soil,
incubation for 3 years.
100
Fig. 2. IR spectra: A – FA; B –
HA; C – Fe-HA-complex; D –
P-treated complex.