California produces more than 80% of the strawberries in the United States and
these systems rely on plastic mulch covered beds that provide many benefits
like saving water and suppressing weeds.
The plastic also creates sustainability challenges
because it's difficult to recycle
and because covering most of the field with plastic creates problems with soil erosion and runoff when it rains.
The erosion and runoff issue really worried me when I began doing organic strawberry research
because the strawberry fields that we were setting up on our research farm
reminded me of the corrugated metal roof
that I grew up underneath in the tropics.
Our roof channeled rain into a tank that gave us our drinking water.
And a similar thing happens in strawberry fields when
rainwater runs off the plastic in the furrows that drain to ditches
that lead to rivers and the ocean.
And this is a problem because of the loss of precious topsoil
and because it reduces recharge of groundwater below the strawberry fields.
We rely on that ground water for irrigation and for drinking water.
The runoff can also carry pesticides and nutrients
that pollute fragile ecosystems that need our protection.
Planting a winter cereal cover crop like
barley in the furrow is a great way to reduce the runoff and soil erosion problems.
And some of my colleagues found that this reduced the turbidity
or the cloudiness of runoff water by about 70%.
But here's the problem
these winter cereal cover crops need to be killed
so that they don't get too big and compete with the strawberries.
And it's hard to control them in a furrow without a grass selective herbicide.
These herbicides are not allowed in organic systems.
And so this inspired me and some colleagues to do research to try to identify
cover crops that are easy to grow and control without conventional herbicides.
And that's what I'll be sharing with you over the next several minutes as I
talk about two experiments that we did over a four-year period.
So this first study was focused on 'Ida Gold' mustard.
It's the type of mustard that produces the mustard that we eat on our sandwiches
It's also got a hollow stem like a straw.
So sometimes I think of growing mustard in these furrows as a
as a way to put straw back into strawberries.
Now in this study we planted the mustard
in mid-november to early December, after we had transplanted the strawberries.
And we planted it at two different seeding rates that I'll call 1x and 3x.
The 1x rate had about 16 plants per foot of furrow
and the 3x rate had about three times more plants.
We let the mustard grow until early February
which was when it was getting around the height of the bed top.
And then we mowed it down with a weed whacker
so that it wouldn't shade the strawberries.
Right before mowing we measured the biomass of weeds and mustard shoots
and here's what we found.
So in this graph our y-axes show biomass in either pounds per 100 feet of furrow
or kilograms per 100 meters of furrow.
And what you can see is that the 3x seeding rate
produced about 60% more mustard shoot biomass than the 1x rate.
And you might think that this increase in mustard biomass at the higher seeding
rate would do a good job of suppressing weeds.
But, unfortunately the weeds still grew really well right along the edge of the plastic at both seeding rates
and here's a graph that shows that.
So in this graph we've got weed biomass
on the y-axes in either pounds per 100 feet or kilograms per 100 meters of furrow.
This is the average weed biomass in a furrow without a cover crop versus weeds in a
furrow at the 1x rate and then at the 3x rate.
So we can see that mustard cover crops reduced weed biomass by about 30 to 40 percent,
but ideally we'd like the weed biomass to be way down here.
And that's a level at which we don't expect the weeds will be able to produce any seed.
Weed seed production in cover crops
is a bad thing because it makes a field more weedy over time.
So the bad news from this first experiment is that we need to do a lot more to control weeds
than just plant a cover crop at a high seeding rate.
But the good news is that Ida Gold mustard was really easy to kill with
mowing with our weed whacker.
Unlike a cereal cover crop that would have just regrown when it was mowed
the mustard died right away.
So that was a real positive thing that we found in this first experiment.
Okay now for the second experiment. This one was focused on several ways to improve weed suppression.
The first thing you might notice is that the cover crop is already at the height
of the bed top and the strawberries have not even been transplanted onto those beds yet.
Now this is a big difference with experiment one where the cover crop
was planted after the strawberries were transplanted.
Now another thing you might notice is that the cover crop in this second experiment has more than just mustard.
We actually mix mustard with Sudan grass which is a warm season cover crop.
We hoped that the Sudan grass would grow well during the relatively warm
period right after planting in late September
and shade out the furrows and suppress weeds, and then die as the weather cooled in the fall and winter.
Now to achieve this earlier planting date, to speed up the planting process
and get the cover crop to grow before the winter rains begin
we developed this special planter.
It allows us to plant the furrows of about one acre of strawberries in one hour
and lay a temporary line of drip tape in the furrow at the same time.
We were then able to apply just a little bit of water to germinate the cover crop and weeds in the furrow,
and then we quickly hand weeded these bare areas near the plastic using this novel hoe that I developed
specifically for use near plastic.
You might want to check it out in this other video and learn how to make one out of recycled materials.
And you can also see it in action it's pretty cool.
Now you might notice that the cover crop looks
thicker on this side of the bed.
In this second experiment we compared the same
seeding rate planted in one line versus in three lines.
And what we found was that the three line pattern shaded the furrow faster and produced about 50% more biomass
which we think will improve weed suppression and probably do a better job of reducing soil erosion.
So here we're removing the drip tape
from the furrow so that we can reuse it again.
And then transplanting the strawberries in early November.
Now the cool thing is that the foot traffic
from the transplant crew helped to push down the cover crop to the furrow bottom
and this reduced the amount of weed whacking of the cover crop that was needed later in the winter.
We're still trying to understand why the mixture was dominated
by mustard in parts of the field and by Sudan grass and other parts.
But in both cases the mixture worked really well to shade out the furrows
and the Sudan grass work just as planned and it died as the weather cooled.
It's been a lot of fun working to put straw back into strawberries
and watching this practice spread among farmers in our region.
It's not a perfect system yet
but we're making good progress to improve these methods and develop new tools
that we think will increase the adoption of this more sustainable and greener way of growing strawberries.
So stay tuned as we continue to refine these practices.
take care !