Increasing the efficiency with which crops use supplied nitrogen
(N) can minimize the impact on the
environment. In the growing seasons 1990/91 to 1992/93, the effects
of different cropping systems on
yield, N uptake by the grain and apparent N-use efficiency (NUE) of the
grain of winter wheat and
winter barley were investigated in a factorial field experiment at Hohenschulen
near Kiel in NW Germany. The crop rotation was oilseed rape–winter
wheat–winter barley, and soil
tillage (conservation tillage without ploughing, conventional tillage),
application of pig slurry (none,
autumn, spring, autumn+spring), mineral N fertilization (0–240 kg
N ha−1) and application of
fungicides (none, applications against pathogens of the stems, leaves and
ears) were all varied. Each
year, the treatments were applied to all three crops of the rotation and
were located on the same plots.
Averaged over all factors, wheat yield was >7 t ha−1
dry matter in all years and N uptake of the
harvested grain varied between 140 and 168 kg N ha−1.
Pig slurry application in autumn increased
grain yield and N uptake more than spring slurry in two out of three years.
Mineral N unfertilized
wheat yielded only 5·3–6·3 t ha−1
depending on the year, mineral N fertilization increased wheat yield
up to 8 t ha−1. Barley yield was lower than wheat yield,
4·5 t ha−1 in 1993 to 6·3 t ha−1
1992. Unlike wheat, spring slurry N affected barley yield and N uptake
more than autumn slurry.
Wheat apparently utilized 12–21% and barley up to 13% of the applied
slurry N for its grain
development. In 1991, the highest apparent slurry N-use efficiency (SNUE)
of wheat and barley
occurred after the late spring slurry application. However, in the following
years, autumn SNUE of
wheat was similar to (1992) or higher than (1993) spring SNUE, presumably
because of vigorous tiller
growth before winter. Additionally applied mineral fertilizer N decreased
Apparent mineral fertilizer N-use efficiency (FNUE) was higher than
SNUE and ranged in wheat
from 40 to 59% and in barley between 19 and 37% of the applied mineral
fertilizer N. FNUE
decreased with increasing N fertilization.
To improve the N-use efficiency of both slurry N and mineral fertilizer
N, more information is
needed about the combined use of both N sources, with special emphasis
on split applications of
slurry as is common practice for mineral N fertilizer.