Which nitrogen fertilization techniques and crop traits promote weed biological regulation by competition?
Résumé
Environmental concerns compel us to reduce agricultural
chemical inputs such as herbicides and mineral
fertilizers, particularly nitrogen. Reduced herbicide use
may increase weeds and reduced mineral fertilization
may limit nitrogen resources. Thus, crop-weed competition
for nitrogen may increase.
Weeds with high nitrogen nutrition requirements are
often hard to manage. They could be disadvantaged
by driving crop-weed competition through an adequate
choice of crop species/varieties (according to their nitrogen
nutrition traits) and/or adaptation of nitrogen fertilization
(rate, date, straw burial or export). This study
aimed to identify which crop traits and nitrogen fertiliza
tion options can reduce weed harmfulness while maintaining
crop production over the years.
A maize monoculture from Aquitaine (France) was simulated
over 10 years and 5 weather repetitions using
FlorSys1. This process-based model simulates crop
growth and weed dynamics over the years with a daily
time step from inputs describing cropping system and
pedoclimate and from species traits. We simulated
many combinations of nitrogen fertilization (dates and
rates, straw burial vs export) and initial soil organic nitrogen
content with three maize varieties (one actual
V1 and two virtual named V2 and V3) differing by their
trait values related to nitrogen nutrition. The effects
of fertilization, initial soil organic nitrogen supply and
maize variety on potential yield and weed (dis)service
indicators were studied.
A sensitivity analysis revealed that maize variety, nitrogen
rate and initial soil organic nitrogen content affected
the indicators the most. Nitrogen date and straw
burial vs export affected them the least. Compared to
the V1 maize variety, in average, V2 improved potential
yield, weed services (weed species richness, bee
food offer) and decreased disservices (yield loss due
to weeds, weed seed production). Variety V3 had the
opposite effect. Depending on their traits related to nitrogen
nutrition, maize varieties reacted differently to
fertilization techniques. For V1 and V2 to a lesser extent,
increasing nitrogen rate increased potential yield,
species richness, decreased weed seed production
and bee food offer. It was the opposite for V3. Increasing
nitrogen rate decreased yield loss for each variety,
it was stronger for V1 and V2 than for V3. Interestingly,
an increase of initial soil organic nitrogen of 50 kg/ha
decreased potential yield by 0.5 to 1 q/ha depending
on the variety.
Further simulations applying optimization algorithms
will be carried out to identify nitrogen dates and rates
that maximize yield, bee food offer and minimize yield
loss.
1Colbach N, et al. (2014), Weed Research, 54: 541-
555. https://doi.org/10.1111/wre.12112