Jf. Power et Ga. Peterson, NITROGEN TRANSFORMATIONS, UTILIZATION, AND CONSERVATION AS AFFECTED BY FALLOW TILLAGE METHOD, Soil & tillage research, 49(1-2), 1998, pp. 37-47
While we know that fallow tillage method affects water conservation an
d soil erosion control, effects on soil and fertilizer N dynamics are
less well known. In this paper, we summarize results from our investig
ations of N transformation and cycling for two experiments established
in 1969 and 1970 near Sidney, NE. In this research, the effects of th
ree fallow tillage methods (moldboard plow, sub-till, and no-till) on
changes in soil properties, N dynamics, and subsequent crop growth wer
e studied. One experiment was on land, that had been broken from sod b
efore 1920, seeded to crested wheatgrass [Agropyron cristatum (L.) Gae
rtn.] in 1957, and cultivated again since 1967 with the above three fa
llow tillage methods. Wheat (Triticum aestivum) was grown in a wheat-f
allow sequence with and without 45 kg fertilizer N ha(-1). The second
experiment was on land that was in native mixed prairie sod until 1969
, and included a comparison of the three above tillage methods in a wh
eat-fallow system with plots remaining in native sod, During the first
13 years of study, total soil N loss from the surface 30 cm of soil (
compared to the native sod) was only about 3% for the no-till system,
compared to 8 and 19% for the sub-till and plow systems, respectively.
For both experiments, considerable mineralization and nitrification o
f organic N occurred during the fallow period, with greatest rates for
plowed fallow. No-till immobilized more labeled and total N in soil o
rganic matter and in visible and partially decomposed crop residues on
and near the soil surface. However, by harvest of the second crop gro
wn after N-labeled fertilizer N was applied, Little if any of the labe
led N was found in visible and partially decomposed crop residues or a
s soil inorganic N, suggesting that most of the fertilizer N applied w
as immobilized in soil organic N or was lost. Deep sampling (to 15 m)
of the Native Sod plots showed that several hundred kg of NO3-N ha(-1)
had leached beneath the crop root zone, presumably during wet years a
fter fallow. For plowed plots, the quantity of NO3-N beneath the root
zone approximated the loss in total soil N from the root zone, suggest
ing there was a little net loss of soil N by denitrification or ammoni
a volatilization. For no-till, quantities of NO3-N beneath the root zo
ne exceeded the loss of total soil N during cultivation, suggesting si
gnificant N-fixation occurred by unknown mechanisms. These results sho
w that fallow tillage system does affect soil and fertilizer N cycling
and transformations and the availability of N to crops. (C) 1998 Publ
ished by Elsevier Science B.V. All rights reserved.