Long-term research is extremely important because it allows us to collect lots of small data
points and slowly over time start to see meaningful patterns emerge.
I'd like to spend a few minutes telling you about an important, long-term, organic system study that we begin in 2003.
The short name for the study is SOCS.
Just like the socks that you wear on your feet.
I'll tell you later why I think this SOCS abbreviation is important
So the SOCS experiment is located in the heart of the Salinas Valley
and it's one of the relatively few long-term, systems experiments
that's focused on high-value, high-input crops.
Cool season vegetables and strawberries are the cash crops in the study,
but I'm going to focus on the first 8 years of commercial-scale vegetable production.
And we'll look at how organic matter inputs from compost
and from a legume-rye cover crop affected several different things.
I'll just focus on 3 systems that will identify with these 3 colors.
All three systems have the same vegetable crops each year
lettuce and then usually broccoli
Now system 3, the green one, it got a legume-rye cover crop every single winter
and system 1 and 2 only got a cover crop every fourth winter and they were fallow the other 3 winters
So cover crop in frequency was a major difference between these systems
Now another way they differ with system 2 and 3 also got yard waste compost right before
each of the vegetable crops but system 1 never got any compost.
This figure shows you the cummulative inputs of organic matter
from cover crop shoots and compost
in the winter, the spring, and the summer of each year.
So with system 1 that never got compost, the organic matter inputs
came from a winter cover crop during year 4 and then year 8.
Now I'll use up pink circle to help us remember that the organic matter here
came from a cover crop.
Now system 2 also was cover cropped every fourth winter
and it also got compost in the spring and the summer.
And then system 3 got a cover crop every winter and compost each spring and summer.
These systems represents 3 very different scenarios
for certified organic vegetable production in our region.
Now here's another graph that shows the total nitrogen input during
the 8 years and vegetable production from
pelleted and liquid organic fertilizers
these are very commonly used in our area,
also from biological nitrogen fixation
that was estimated based on the growth of the legume component in the cover crop.
And then from compost in system 2 and 3
Now it's important to remember that in all other aspects of the systems during vegetable production
there were no differences in terms of tillage, irrigation, weed management, etc.
The only way that they differed was in terms of cover cropping frequency
every year vs. every fourth year, and then compost.
So let's look at some of the results on how these three different management strategies affected lettuce yields
because this is the Salad Bowl of the world
soil health because this is an important and hot research topic right now
and then phosphorus budgets,
because phosphorus plays a critical role in our bodies
and it's also a limited resource that needs to be more carefully managed.
So in this area lettuce is often packed in boxes of 24 heads
and usually a box needs to weigh about 30 pounds to be marketable
We'll start with system 3 that got compost and the winter cover crop every year.
So these large dots connected by the line
are the average yields and the small dots are the four replicates that show the variability in the data.
in most years the average marketable yield was at least 1000 boxes per acre in this system
this is excellent.
Now in system 2 that got compost but was only cover cropped every fourth winter
look at how bad the yields were the first 3 years and how they were highest during year 4 and year 8.
Now the same basic pattern with high yields during year 4 and 8 also happened in system 1 that never got compost
and was only cover cropped every 4th winter
Now let me combine these 3 plots so that we can see the major trends
So what's going on here? Why did the yields of system 1 and 2 increase dramatically during year 4 and year 8?
Well, I think it's because system 1 and 2 got a winter cover crop right before the lettuce of year 4 and year 8.
And this shows the remarkable power of a cover crop to boost yields.
So how does a cover crop do this? Well, here's what I think is happening.
Remember that these are high input organic systems where we had lots of nitrogen rich fertilizers to the vegetables.
The nitrogen input from the fertilizer in broccoli was usually about 160 kg per hectare each year
And when a crew like this harvests the broccoli, only about 25% of the total shoot biomass,
that is just the top part that we eat, is removed from the field.
So in other words, most of the nitrogen in the broccoli plant is left in the field in nitrogen-rich leaves and shoots
So these leftover parts are mowed and then incorporated back into the soil.
and if the field was left in a bare winter fallow after broccoli
all that leftover nitrogen can leach out of the root zone and down into the groundwater.
But when you have a winter cover crop after the broccoli, the cover crop is able the capture
the leftover nitrogen and recycle it back into the next spring lettuce crop
Now you might be wondering whether the nitrogen fixation by the legume component in that cover crop mixture
also help to increase yields and system 1 and system 2 right after they were cover cropped
This may have helped a little bit, but I don't think it did much because we also have
high lettuce yields in other systems and the experiment where we grow only non-legume cover crops every year.
So I think of the primary nutrient management benefit of winter cover cropping
in these high-input organic systems is to improve nutrient cycling and storage
which can reduce fertilizer inputs and protect the groundwater.
Okay, so now let's talk about soil health. Now to do this I'm going to use microbial biomass carbon which
is a sensitive biological indicator of soil health.
The size of this diverse microbial community or its biomass is important
because these wonderful microbes regulate the transformation and the storage of nutrients in the soil
They're the living part of soil organic matter.
Generally, as the microbial biomass increases so does soil health.
So here's a graph that shows the change in microbial biomass carbon over the first 6 years of vegetable production
these bars are the 95% confidence intervals with the average in the middle and then the raw data of the four replicates.
So it's very clear that the greatest improvement in soil health was in system 3 that was cover cropped every winter and got compost.
in contrast, there was some evidence of an actual decline in system 1
and just a slight improvement in system 2 that also got compost but was seldom cover cropped.
So these data agree with the lettuce yield data in the benefits of frequent cover cropping.
Now for the phosphorus budgets during the first 8 years of vegetable production
So these bars represent the amount of phosphorus that went into the systems from
fertilizer, compost, cover crop seed, and vegetable transplants.
and the second bar here in each of these systems shows the amount of phosphorus that was taken out in the harvested vegetables
So it's very clear that we applied far more phosphorus than was needed in the systems.
In other words the nutrient budgets in these systems were not in balance.
Now I've been interested in balance for many years... long before I became a scientist
this is me as a teenager in my home country of Papua New Guinea, with one of my friends
And I realized that if you want to go far... you've got to have good balance
The concept of balance also applies to our agricultural systems.
For them to be sustainable they have to be balanced in many different ways.
and the imbalance that I've seen with phosphorus in our long-term study
makes me question the organic regulations which prohibit farmers from using pure synthetic nitrogen.
This regulation often leads us to apply far more phosphorous in these high-input organic systems
as we try to meet the nitrogen needs of the crops.
Now you might want to check out this other video that I made where I suggest that organic
farmers should be allowed to use pure synthetic nitrogen.
Now as you can tell, I didn't wear shoes or socks when I was a lot younger.
And I still occasionally enjoy going barefoot at work.
But usually I wear socks because they help to protect my feet
in our world as it's become more and more crowded.
I like the abbreviation for our study, SOCS
because it reminds me of my feet
and about the footprint over agriculture on the world and
and the importance of developing systems that minimize that footprint.
SOCS also reminds me that to make progress in a journey you have to have lots of socks.
You can't just have one sock on one foot. What about the other foot?
It won't be very happy.
In other words we need lots of long-term studies.
I hope that tomorrow when you put on your socks
you think about the SOCS experiment and why this type of long-term research is critical.
Thanks for listening.