I'm going to be talking about cover cropping strategies for climate smart
farms. And I'll focus on cover crops because I
think they're an essential part of sustainable vegetable production.
Here's a paper I wrote about this that you might want to check out. There's a
link to it in the video description along with links to other articles and
videos you might find interesting, and there's also a clickable table of
contents in the video description to the different parts of this video. But I want
to start off with a joke from a very thought-provoking article
by a reporter who had been at the climate summit in Glasgow.
The joke goes like this: Two planets are talking to each other,
one looks like this beautiful blue marble
and the other looks like this dusty brown ball.
"What on earth happened to you?" the beautiful planet asks the brown one.
"I had Homo sapiens" answers the brown planet, "Don't worry" says the blue planet
"They don't last long." Now it's true that in earth's geological
time that's shown here as a spiral we humans, Homo sapiens, haven't been around
long. We evolved during the Pleistocene and we didn't invent agriculture until
about 10,000 years ago during the Holocene when the temperatures on earth
were relatively stable. Here's a graph that shows the
temperature variability during the past 100,000 years with lots of stability
during the Holocene when agriculture was developed.
Now as we change our planet's climate we don't know if our farms will be able
to feed us and that's why it's critical that we work together to reduce our
greenhouse gas emissions that are changing our planet's climate and
threatening our survival. Here's a really good video that I think
did a good job of explaining this risk and here's another one that really
helped me to understand climate-resilient farms.
Now one image that comes to my mind when I think of climate resilient agriculture
is the little tin canoe that I made when I was growing up in Papua New Guinea.
I loved paddling my little canoe out to a small island where I'd fish and
explore. I'd go out there in the early morning
when the water was calm and glassy. But I knew that in the afternoon I
needed to be careful to paddle back to the main island
before the wind got too strong and the big waves could easily sink my little
tin canoe. The weather was predictable just like
it's been on earth for the past 10,000 years.
But if the weather hadn't been predictable, what could I have done to
make my little canoe more stable and resilient? Well, I could have added a
wooden outrigger or two to prevent it from tipping over.
And to increase my efficiency of getting places I could have added a mast and a sail.
Now in my mind these modifications to my
little canoe can symbolize what farmers will need to
do to develop creative solutions to add 'shock absorbers' to their farms
to make them more resilient and efficient and therefore more likely to
stay afloat and adapt to the challenges of climate change
Okay now for the cover cropping
strategies for climate smart farmers. I'm going to focus on the Central Coast
of California where I've been doing lots of cover cropping research for the past
20 years. It's a part of California that's
extremely vulnerable to climate change but the future of cover crops here is
bright and that's because of a new regulation that's focused on reducing
nitrate leaching into our groundwater. This regulation gives farmers a major
incentive for winter cover cropping.
This is great, but I can also see three climate-change related challenges with
increased cover cropping. The first one has to do with
water use by the cover crops. So cover crops provide all kinds of
ecosystems services, but they also use water, and depending on
how they're managed they could actually reduce groundwater
recharge. Which wouldn't be good.
If you want to learn more about this complex issue check out this paper.
The second issue is that as the climate warms, the production of some cool season
vegetables might have to shift from the summer
because it's too hot in the increasingly mild winter,
and this could leave less fallow land available for winter cover cropping,
And the third potential challenge has to do with the availability of cover crop seed
due to the increased demand and limited
supply of that seed. I've found that the seed supply of popular
cover crops like rye often runs out in the fall, but this year it happened much
earlier because the entire seed production of a relatively new rye
variety that I helped to introduce to the area several years ago, was wiped out
by the heat wave that occurred in the pacific northwest where the rye seed was
being produced. A recent analysis found that this heat
wave was virtually impossible without human-caused climate change.
So keep these different challenges in mind as I talk about cover cropping strategies
Okay, so the first strategy
is to pay close attention to your cover crops and measure them.
You might wonder how does this help you. Well here are two ways.
First, if you're a farmer in the Central Coast of California
this will help you to get the nitrogen credit for growing a non-legume cover
crop in that new regulation that I mentioned earlier.
The regulation has three requirements for cover crops. The first one is pretty
easy. You just got to keep track of the planting and termination date of the cover crop
But how's a grower supposed to meet the
second two requirements without a drying oven or tissue analysis?
Well don't worry, my friend Richard and I are running
several trials this winter to figure out simple ways that farmers can easily meet
the second two requirements. So far our data suggests that cover crop height
can be used as an estimate for biomass.
And we expect that cover crop developmental stage
will be a good estimate of the cover crops carbon to nitrogen ratio.
Stay tuned for more on that. Now the second reason you want to pay
close attention to your cover crops is that it will actually allow you to
get more benefits from them. Let me give you a very specific example.
One of the main reasons we grow cover crops is to add organic matter to the
soil, right? Well after you spend all that money on seed and planting costs and
irrigation you want to make sure that you get as
much organic matter as possible. So how do you know if your cover crop is
still producing organic matter. Well here's an example from a growers field
that I sampled recently. So this graph shows how the cover crops biomass
changed over time. The grower had removed the pipe from the
field and told me initially that they wanted to take the cover crop down on
this date. And based on the cover crops growth
stage and the cover crops height from a few random plants
I knew that the cover crop still had a lot of potential to grow.
So I suggested that they hold off a week or two before disc in the cover crop.
And here's the cool thing just by waiting one week they increased the
cover crops biomass, the shoot biomass by 37 percent, and waiting two weeks
they increased it by 50 percent. Pretty cool right?
Well guess what, here's also what's cool. The amount of biomass in that field
captured the same amount of carbon dioxide from the air above that field
that would have been released by burning over 500 gallons of gasoline.
If you want to see how I calculated that check out a link in the video
description. By the way, here are the three basic
tools that Ilike to use when I measure my cover crops. A measuring tape to get
the cover crop height. A lettuce knife to dig up plants in a
few feet of row to measure to see how much of the seed
that I planted actually emerged, we don't want to waste seed.
And then a free smartphone App that you can use to take a photo of the
cover crop and then instantly determine the percent ground cover of that cover
crop. And that ground cover is related to the ability of the cover crop to shade
out weeds. Okay, the second strategy is to be very
cautious with cover crop mixtures especially those that include legumes
and cereals. Now I've spent a lot of time in legume-
cereal mixtures over the past 20 years trying to understand how the legumes
compete with the cereals. Several years ago I made a video where I
questioned if legume cereal mixtures were a good fit in organic vegetable
production. I hope you'll check that video out.
But essentially my long-term research with mixtures has shown that legumes
don't compete well with cereals, especially
when the rainfall is limited and early fall temperatures are warm.
Now both of these are much more likely to happen as the climate changes in
California. So when you're choosing cover crops
think about the drought tolerance of the cover crop.
All right now the third strategy is to try to reduce tillage as you transition
from a vegetable to a cover crop. Now I know there's a lot of interest and
potential benefits to reducing tillage and vegetable systems
but believe me it's not easy especially if you can't use an herbicide
and if you're trying to plant a vegetable into a thick
mat of cover crop mulch. I made a video a few years ago about
some of the benefits and challenges of tillage that you might want to check out.
Now one of the easiest ways that I think we can potentially reduce tillage in
high value vegetable systems could be when we transition from a vegetable to a
winter cover crop. This might work because in contrast to
most small seeded vegetables that need a very fine seed bed to get a nice uniform
stand cover crops are pretty tough and
flexible and can germinate without a lot of careful soil preparation.
And you might be able to actually just mow the vegetable
and leave the residue on the soil surface to conserve moisture and help to
slow down the release of nitrogen as that residue decomposes,
and then you could drill the cover crop right into the vegetable beds.
here's an example of where a cover crop was drilled between the rows of mowed
vegetables. In this case the mowed vegetables regrew along with the seeded
cover crop. That's okay as long as the vegetable
regrowth doesn't cause a pest or disease issue.
Now if you don't want vegetable regrowth you could mow the vegetable
and then undercut it to kill it before drilling the cover crop through the
mulch. Who knows you might even be able to
leave the drip tape from the previous vegetable crop
on the soil surface and then use that to irrigate the cover crop. I think it's
worth trying. And that leads me to my last strategy
which is to think out of the box and experiment and innovate like crazy!
There are so many innovative ideas that need to be tried.
I'm here to help and I love working with farmers to design simple experiments
that evaluate their ideas. One of my more novel and somewhat crazy
cover cropping ideas is described in this video. I'm still working on this so
stay tuned, but the cool thing about this juicing strategy, from a climate change
perspective, is that it would allow the cover crop to
scavenge nitrogen and protect groundwater
while using relatively little water and producing about half as much biomass as
a standard cover crop. And then the grower can just use that
juice as a fertilizer for the next vegetable
and the cover crop biomass or the pulp from the juicing process as a soil
amendment when it's convenient. Check out that video when you get a
chance. Anyways, thanks for listening, and I hope
you do your part to support climate smart farmers
and help to protect the beautiful blue planet that we call home.
We don't have a lot of time left to figure out this climate change crisis,
but if we work together we can do it. Don't forget to check out the other
resources in the video description and take care!
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