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March 15, 2007: We’ve had time to
compile the numbers behind Paul
Hepperly’s report in January on organic no-till
corn yields from our fields in 2006. Readers sent in several
queries, so we want to share those along with the details
of the growing conditions and practices that generated those
yields (so you can adapt what we learned to your own fields).
The organic no-till corn yield of 160 bu/ac cited by Dr.
Hepperly was an average harvested from two of our production
fields. Because these fields were planted solely for production,
we did not measure their hairy vetch seeding rates, cover
crop biomass, corn plant populations or weed biomass. They
were harvested with a standard combine, and the grain collected
from three measured field passes was commingled then weighed.
The standard-till organic corn yield of 143 bu/ac was taken
from a single production field using the same method, while
the non-organic chisel-plow yield of 113 bu/ac was harvested
with a research combine from our Farming Systems Trial (FST)
conventional system (a yield average from eight plots that
total about 1.1 acres).
We also planted 1 acre of organic no-till research corn that
generated an average of 146 bu/ac from 24 plots of 20x50 feet.
In this research field, we gathered a lot of the specific
information you requested concerning:
- Field history prior to the no-till corn
- The type of cover crop used
- How the cover crop was established (when, with what equipment,
at what rate)
- How the cover crop was killed and incorporated
- How N was made available to the crop
- What corn variety was planted
- How the corn was planted
- Growing conditions for the season
- Comparative yields for the region
- Input costs
It’s important to note that the topography and soil
types on our research farm vary considerably from one field
to another, and sometimes even from one end of a field to
the other. Consequently, the yields from these fields will
vary as well (even if all other treatments and practices are
the same). For example, the no-till production yields were
taken from fields that lie low on our farm and have excellent,
deep top soil, while the no-till research yields were harvested
from a hill-top field that has a thinner layer of top soil
and faster drainage. These differences in soil quality and
water retention likely caused some part of the yield difference
between the production and research organic no-till yields.
Field history
In the two organic no-till corn production fields, hairy
vetch was planted in September 2005 following small grain
harvest and an August application of compost. (The compost
was applied onto stubble at 8 to 10 tons/ac [wet weight] and
moldboard plowed for incorporation.) In one field, oats had
been preceded by a crop of soybeans, which had been relay
cropped into winter wheat in 2004. In the other field, winter
wheat had been preceded by oats in 2004 and compost was also
applied in August 2004 following the oat harvest.
In the standard-tilled organic field, corn was planted in
May 2006 after plowdown of poultry manure and a 2-year-old
alfalfa hay field, which had been frost seeded into wheat
in March 2004.
In the research no-till corn field, winter wheat was planted
in early October 2004 and harvested in July of 2005, followed
by the incorporation of compost in August and drilling of
hairy vetch in September. Click
here for a diagram of different field histories.
Cover crop variety and planting particulars
We used hairy vetch as our cover crop in all our no-till
and standard-till organic corn. The vetch was planted with
a grain drill in late August or early September (depending
when the previous crop was removed and compost applied). Hairy
vetch needs to be sowed 40 to 60 days before the first killing
frost in order to form N-fixing root nodules, produce enough
biomass and store enough carbohydrates to survive the winter.
(Hairy vetch cultivar choice and individual plant genetics
also influence winter survivability. For example, planting
hairy vetch seed from north of our latitude reduces winter
kill.)
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If you are planting hairy vetch for the first time in your
field’s history, you’ll need to inoculate your
vetch seed with a pea-vetch inoculum before planting (Rhizobium
leguminosarum, type C [pea]). We recommend inoculating
your vetch seed every time you plant in order to support optimal
growth and N fixation (an inoculum packet is often included
with vetch seed purchases), but for a first-time planting,
inoculation is vital.
In the research field plots, the vetch was planted at a rate
of 25 lbs/ac and produced an average total biomass of 6,146
lbs/ac by the time it was rolled down for corn planting on
June 9. The average N content of this biomass was 3.31 percent,
or about 203 lbs/ac. (Biomass and N content data were not
collected from the production fields.)
Cover crop incorporation and corn planting
In early June, the hairy vetch in both the research and production
no-till fields was rolled down with a front-mounted
Rodale Institute-designed roller/crimper. In the same
field pass we planted Blue River 68F32 corn with a rear-mounted
four-row Monosem no-till planter.
The planter is a hybrid composed of a Monosem vacuum seed
pickup attached to a Kinze toolbar planter, equipped with
15-inch fluted disk blades to cut through the rolled vetch
mat, followed by a 15-inch double-disk opener and then a pair
of 12-inch cast-iron closing disks and a plastic Keeton seed
firmer. Extra weight is added to this planter to help it cut
through the thick hairy vetch mat into the soil surface for
effective corn establishment.
There was no further incorporation of the hairy vetch; the
rolled vetch mat was left on the soil surface to decompose
naturally and suppress weeds.
The research corn plots were planted at a density of 32,000
seeds per acre, and the pre-harvest population count averaged
24,533 plants/acre. A large portion of this population reduction
was due to cutworm damage. In coming years, we are planning
to address this issue either by delaying the planting date
and/or applying Bt and diatomaceous earth as we plant.
Growing conditions in 2006
Blue River 68F32 is a full-season corn with a relative maturity
rating of 113 days. During the 2006 growing season, we accumulated
2,140 growing degree units between June 9 (the research plot
planting date) and the end of September, when the corn reached
full maturity. Rainfall for this period was 26.5 inches, 10.44
inches above average for that time period, based on 30-year
records.
Comparative yields around the region
As reported, the average corn yield of the two organic no-till
production fields was 160 bu/ac, while the no-till research
field plots averaged 146 bu/ac over 24 plots. The standard-till
organic production field yielded 143 bu/ac, while the Farming
Systems Trial’s (FST’s) standard-till organic
plots yielded 139 bu/ac in the manure system (which received
compost but no vetch N inputs) and 132 bu/ac in the legume
system (which received vetch but no compost). At the same
time, the FST’s non-organic standard-till field yielded
113 bu/ac.
To compare, the Berks County average non-organic corn yield
for 2006 was 130 bu/ac, and the average yield for Southeastern
Pennsylvania was 147 bu/ac (Click
here to see chart).
Cost analyses
Hairy vetch seed costs $50 to $75 per acre. Given the estimated
N output of the hairy vetch biomass in the research field,
the cost of the hairy vetch N averaged 25 cents to 37 cents
per pound. In comparison, our conventional N fertilizer cost
approximately 50 cents per pound in 2006.
It is important to note that not all the N generated by the
hairy vetch biomass is available for plant use. Some is lost
to volatilization and some is retained in the soil organic
matter. However, vetch is not the only N source available
to our corn crops. After years of organic production, our
farm’s soils have received many cover crops, crop residue
and compost inputs that have increased the soils’ organic
matter and microbial activity.
The N in these soils becomes more available as the soil warms
in the spring and feeds plant growth steadily over the growing
season. Thus, the hairy vetch provides N for the season’s
crop and also acts as a soil conditioner to improve the long-term
nutrient availability and performance of our soils. These
factors make N cost analysis more complex, but the long-term
benefits showcase the system’s advantages.
At the same time, the rolled mat of hairy vetch limited weed
biomass to an average 1,170 lbs/ac in the organic no-till
research plots, with particularly excellent control during
the critical third- through eighth-leaf growth stage. Weeds
do eventually break through the hairy vetch mat, but at a
later point in the season when they do not pose a competitive
threat to the corn. Therefore, weed management benefits must
also be calculated as part of the vetch seed expense, including
the elimination of five to seven field preparation and cultivation
passes (reducing tractor wear, diesel use and labor).
Final thoughts
Keep in mind that The Rodale Institute’s organic no-till
rotation is not designed as a continuous no-till system. Tillage
is used to incorporate residues or inputs and to prepare seed
beds at different points in the rotation. For example, after
the no-till research corn was harvested, the field was disked
and a winter rye cover crop was planted into the corn stubble
and vetch residue. And so the cycle continues.
Any reduction or elimination of tillage can improve soil
quality and nutrient retention, but our research shows that
judicious tillage, when coupled with organic soil improvement,
can create soil benefits that surpass those of continuous
conventional no-till systems. Thus, we will continue to develop
our organic no-till rotation in combination with other proven
organic practices to strike a successful balance of soil improvement,
weed control, yield and economic viability. 
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