Hi,
Technically cereals are "semelparous plants"
These are monocarpic plants with a single reproductive event. So when
the plant flowers it then dies. Of course these include the annual
plants, but also some quite long-lived plants (remember some of the
bamboos will grow vegetatively for years, flower once and then die).
The survivorship curves of such plants all show a dramatic increase in
mortality following flowering. In semelparous plants all of the
meristems of the plant die following flowering, and thus the whole
plant dies. The mechanism of senescence in such plants is not known,
but it seems to be related to the mobilization of plant resources to
produce developing seeds.
My suspicion is that if you tried to genetically engineer cereals to
become annuals then you would radically reduce grain yields. "You can't
get something for nothing".
Best Wishes,
Martin Hodson

wrote:
I am wondering why cereals such as oats and wheat need to be planted
every year, at expense (labour and machinery). The grass on my lawn
seems to keep growing from year to year, even after cutting.

Does wheat die after ripening and forming seed? Even if the plants
lasted two years before ploughing and e.g. growing beans then that
would save a lot of fuel. Is this what zero tillage is about? Is
ploughing needed to cut down on weeds?

Can you buy perennial cereals, or are there people working on
breeding
(or genetically engineering) them?

Dave.