Ht. Dou et D. Steffens, RECOVERY OF N-15 LABELED UREA AS AFFECTED BY FIXATION OF AMMONIUM BY CLAY-MINERALS, Zeitschrift fur Pflanzenernahrung und Bodenkunde, 158(4), 1995, pp. 351-354
A greenhouse experiment was conducted with Lolium perenne to determine
whether ammonium (NH4+-N) fixation by clay minerals can increase the
recovery of nitrogen following application of N-15 labelled urea. A si
lty loam subsoil, B-1 horizon from an Alfisol derived from loess, pH (
CaCl2) 7.9, was chosen for the experiment. The NH4+-N fixation capacit
y was altered by varying the distribution of potassium (K) in the uppe
r and lower soil layer. In the K-0 treatment (control), the upper soil
layer fertilized with urea was not supplied with K, whereas the lower
soil layer was fertilized with 300 mg K kg(-1) soil. In the K-1-, K-2
- and K-3 treatment the upper soil was supplied with 100-, 200- and 30
0 md K kg(-1) soil, respectively. The soil in the lower layer of the K
-3 treatment was not supplied with K. The recovery of N-15 from applie
d urea (N-15 uptake of Lolium perenne plus residual soil N-15(1)) was
86.1% in the K-0 treatment and 75.2%, 69.1% and 69.6% in K-1-, K-2- an
d K-3 treatments, respectively, showing that N-15 losses were smallest
in the K-0 treatment. Two weeks after applying N-15 labelled urea the
amounts of nonexchangeable (NH4+)-N-15-N in the upper soil layer were
significantly higher in the K-0 treatment than in the treatments with
K application. Apparently, NH4+-N fixation by clay minerals can reduc
e NH3 volatilization after urea fertilization, if the amount of exchan
geable K is low.