2005: Maintaining adequate soil nitrogen levels is the
first concern of many farmers considering transitioning to organic
production. But by growing legume cover crops, soil nitrogen levels
can be increased to optimize organic production in short order,
even on heavily demanding crops such as corn.
Another option for raising soil nitrogen rapidly is the addition of
compost and/or manure to supply the rate of nitrogen needed for the
target crop. For those that have a hay market, alfalfa/grass hay production
is particularly suitable for building soil nitrogen during the transition
to organic production.
"We have a production system that
will produce nitrogen, control erosion, uses energy efficiently,
helps control weeds and insects and solves farmer economic
problems. It’s free and [it's] called rotation."
- John Vogelsberg, Researcher
In The Rodale Institute Farming Systems Trial®, now in its
25th year, we have increased soil nitrogen from 0.29 percent to
0.34 percent by utilizing mixed organic rotations and cover cropping.
Control plots managed in a conventional corn-soybean system have
seen soil nitrogen fall slightly, from 0.29 percent to 0.28 percent.
Normally, as soil organic matter increases under organic management,
soil nitrogen limitations are resolved.
In terms of building soil nitrogen, it's hard to beat hairy vetch,
which can fix over 200 pounds of nitrogen per acre under favorable
conditions. We plant hairy vetch in August after small grain harvest
and turn the green manure under in early May before planting corn.
We get our nitrogen for the cost of growing and turning under the
In addition, we like to mix oats with hairy vetch. The oats give
early fall weed control and reduces the seed cost on the legume.
Stands that are a 50-50 mix of oats and hairy vetch can produce
the same levels of nitrogen as hairy vetch alone.
Speaking of weeds, two-thirds of farmers we surveyed recently say
weeds are their number one production challenge. Our experience
supports that view, and we are working with the Pennsylvania State
University and the USDA-ARS Sustainable Agriculture Laboratory on
In the last two years, we have shown that some corn and soybean
varieties tolerate weeds better than others: With the same weed
pressure, yield losses ranged from less than 10 percent up to 60
percent. We have also seen that if weeds are less than 1000 pounds
per acre in dry matter, significant crop yield losses are minimal
even with susceptible soybean varieties.
As with soil nitrogen, cover crops are a key to organic weed management.
Using rye as a cover (with up to 8,000 pounds per acre rye dry matter),
weeds are greatly reduced in both susceptible and weed tolerant
Organic systems are not something that can be created over night.
McSorley (2002) argues that a central focus of the transition period
should be lowering pest populations and achieving a biological balance
that will maintain a high level of plant health.
In Maryland, researcher Ray Weil is demonstrating the ability of
oil radish and rape to produce a biological fumigation and sub-soiling
effect through the generation of natural cyanide and roots powerful
enough to fracture the clay hard pan.
Although transitioning to organic may seem fraught with pitfalls,
you can see that we have a wide array of effective biological strategies
to meet the principal challenges. John Vogelsberg (1987) summarized
it this way: “We have a production system that will produce
nitrogen, control erosion, uses energy efficiently, helps control
weeds and insects and solves farmer economic problems. It’s
free and [it's] called rotation.”