Summary
Since the year 2006, the detection of soil active herbicides and their metabolites increased in
groundwater in Germany. In areas with continuous maize cropping systems, metabolites of the
soil active ingredient S-Metolachlor are frequently detected. Due to its good soil effect, S-Metolachlor
is an important component in numerous herbicides.

A three-year field experiment was conducted to test, if continuous maize cropping with
intercrops allows dispense on soil active ingredient S-Metolachlor. Yield losses and an
uncontrolled spread of adapted weed species should be avoided.

We tested two maize cropping systems with foliar active herbicides and intercropped grass
against the previous standard system without intercropping and the use of soil-active herbicide
S-Metolachlor. In the cropping system `Lolium spp. intercropping´, we dispensed the
application of soil-active herbicides. In the cropping system `Festuca spp. intercropping´, we
additionally avoid the use of herbicides against monocot weed species.

The experiment based on four questions. 1) Has the adaption of the herbicide treatments in the
tested cropping systems a distinguishable effect on weed vegetation? 2) Is weed density equally
controlled by the tested cropping systems? 3) Is repeated maize cropping with intercropping
grass possible without a spread of individual weed species? 4) What effect has maize cropping
with intercropping grass on yield?

1) The efficacy of the herbicide treatment in the cropping system `Lolium spp. intercropping´
was as effective as the herbicide treatment in the cropping system without intercrop and use of
soil-active herbicide S-Metolachlor. In contrast, in the cropping system `Festuca spp.
intercropping´ we observed an insufficient herbicide efficacy against the monocot species Poa
annua.

2) The weed densities in the tested cropping systems only differed after maize harvest in the
winter months. The weed density of the cropping system `Lolium spp. intercropping´ was
smallest in all years. In the cropping systems `Festuca spp. intercropping´ and `without
intercropping´, the weed density increased. In the second and third year of the experiment, the
weed density in these cropping systems were significantly higher in comparison to the cropping
system with `Lolium spp. intercropping´.

3) The cropping systems differed in the control of individual weed species. In the maize
cropping system with `Festuca spp. intercropping´, dispense on herbicides against monocot
weed species caused an increase in the density of Echinochloa crus-galli and Poa annua. In the
cropping system `Lolium spp. intercropping´ the density of E. crus-galli increased during the
three-year period, however non-significantly. In the cropping system `without intercropping´
P. annua was not sufficiently controlled. In every year the density of this species was in the
cropping system no intercropping higher than in the cropping system `Lolium spp.
intercropping´.

4) In this experiment, the three cropping systems did not differ in their maize yield quantities
in any year. The different weather conditions during the experimental period affected the yields
of all cropping systems the same. In contrast, the dry matter content increased significantly in
maize cropped with `Festuca spp. intercropping´. Thus, maize in this cropping system was
ready for harvest earlier.

Over a three-year period, the cropping system with Lolium spp. as intercrop confined weeds as
effectively as the common practice using S-Metolachlor. The differences in weather conditions
confirm the robustness of the `Lolium spp. intercropping´ system. No yield losses were
observed. Only the control of Echinochloa crus-galli represents an uncertainty for long-term
maize cropping in this system.