Organic Matter and Sustainability - Sustainable Management of Soil Organic Matter - page 31

However, differences in absorption intensity are not as distinct as in the
samples with the low application rate. We hypothesize that, because of the
lower input of organic fertilizer at Müncheberg (32 dt ha −1 year −1 ), miner-
alization prevents a significant increase in C org content in the fertilized soils
at this site compared with the sandy site at Groß Kreutz with a higher
FYM dm application rate (50 dt ha −1 year −1 ). The absorption intensity of the
C = O band in the FT-IR spectra of the sodium pyrophosphate extracts
indicates a similar effect of the type of fertilization on SOM composition as
shown for the spectra of the hot water extracts.
The absorption intensity at 1710 and 1690 cm −1 correlates with the
CEC of the SOM extracts. A high absorption intensity indicates a high
CEC value. As the SOM extracts of the samples from the FYM + N plots
show the highest absorption intensities at 1710 and 1690 cm −1 ,we
expected the highest CEC values for these samples. This corresponds to
the finding that the soil samples of the FYM + N plot of all long-term
field experiments show the highest CEC (Table 1.2.3) due to differences
in SOM composition. However, the information from the spectra is only
partially representative for the CEC of the soil samples as the extracts
represent certain parts of SOM, only.
However, the differences in the absorption intensities of the hot water
extracts are higher for the loamy soil than for the sandy soils. A possible
explanation is that at the loamy soil site a higher amount of farmyard
manure (Table 1.2.2) was applied than at sandy soil sites. This results in a
higher C org content in the loamy soil (Table 1.2.3) and may correspond-
ingly lead to a higher content of carboxyl groups also in the hot water
extracts. It may also be possible that the hot water-extractable SOM is
protected against mineralization by the higher clay content at the loamy
soil (Stevenson, 1982). However, for the sodium pyrophosphate extracts,
the reverse is found. This may be caused by the higher clay content in
the loamy soil. SOM seems to be protected against extraction due to
complexation with clay minerals.
Conclusions
The fertilization regime influences the C org content, CEC and SOM
composition of all studied long-term field experiments. Relatively low
input of organic fertilizer, 32 dt year −1 for the sandy soil at Müncheberg,
results in non-detectable differences in C org content and CEC between the
different fertilized soils. The characterization of SOM by FT-IR spectra of
sodium pyrophosphate and hot water extracts shows that the composition
of SOM from the loamy and sandy soils was affected by the type of
fertilization and the amount of organic fertilizer. Comparing the long-term
field experiments from a loamy and a sandy soil, we conclude that the