K. Mengel et al., Nitrogen compounds extracted by electroultrafiltration (EUF) or CaCl2 solution and their relationships to nitrogen mineralization in soils, J PLANT NU, 162(2), 1999, pp. 139-148
Citations number
44
Categorie Soggetti
Environment/Ecology
Journal title
JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE-ZEITSCHRIFT FUR PFLANZENERNAHRUNG UND BODENKUNDE
The objective of the investigation was to identify the most important organ
ic N-containing fractions extracted from soils by electroultrafiltration (E
UF) or a CaCl2 solution, respectively, and their importance for nitrogen mi
neralization. The investigation comprised 19 agricultural and one forest to
p soil. Net N mineralization was tested in Mitscherlich pot experiments wit
h three treatments: (1) fallow soil without N fertilizer, (2) soil cultivat
ed with lye grass without N fertilizer, (3) soil cultivated with rye grass
with N fertilizer. The highest proportion of N in the extracts was the amin
o N fraction (amino acids + peptides) amounting to approximately 60 % of th
e total N extracted by CaCl2 and to about 40 %, of the total N extracted by
EUF. The proportion of amino sugars from total N extracted was in average
10 % for the CaCl2 and 5.2 % for the EUF extracts. The proportion of hetero
cyclic N bases derived from nucleic acids amounted in average to 4.8 % and
3.6 % for the CaCl2 and EUF extract, respectively.
Amino N (amino acids + peptides) were correlated best with net N mineraliza
tion (EUF, r = 0.81***, CaCl2, r = 0.86**'). The correlation between amino
sugars and net N mineralization was r = 0.55* for the EUF extract and r = 0
.49* for the CaCl2 extract. The heterocyclic N bases did not correlate with
net N mineralization. Correlations between Norg extracted by CaCl2 versus
net N mineralization were higher than those obtained by the EUF extract.
Net N mineralization was about four times higher in the fallow soils than i
n the treatment with grass and no N fertilizer. In the treatment with grass
+ N fertilizer on average no net N mineralization occurred, moreover there
was a tendency of N immobilization. It is assumend that in the treatments
with grass cultivation, organic C released by roots stimulated the assimila
tion of mineral N and amino acids by soil microorganisms resulting in a low
net N mineralization. Net N mineralization led to a highly significant dep
letion in the Norg pools and particularly in the amino N and amino sugar po
ols in the treatment with grass and without N fertilizer. This depletion wa
s particularly evident in the CaCl2 extracts. The results justify the concl
usion that the Norg obtained with both extraction methods originates from a
dynamic N pool into which N flows in and out. The amino N extractable with
EUF or CaCl2 is a reliable indicator for the net N mineralization potentia
l of soils.