16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/11539
Performance of Organic Grain Cropping Systems in Long-Term
Experiments
Teasdale, J.R.1 & Cavigelli, M.A.1
Key words: organic farming, no-tillage, crop rotation, soil carbon, weed control
Abstract
Organic farming and conventional no-tillage farming systems share many of the same
benefits from protecting and improving soils. A review of recent results from two longterm systems experiments in the mid-Atlantic region of the U.S.A. demonstrates that
organic cropping systems with organic amendments can increase soil carbon,
nitrogen, and yield potential more than conventional no-tillage, despite the use of
tillage in organic systems. However, reduced-tillage organic systems present
challenges for weed control, particularly with simple rotations typical of conventional
grain cropping systems. Organic systems that employ more complex rotations
including a hay crop have demonstrated greater potential for improved weed control,
increased nitrogen availability, and increased yields.
Introduction
Conventional grain production in the mid-Atlantic region of the U.S. is characterized by
short rotations [primarily maize (Zea mays L.), soybean (Glycine max L. Merr.), and
wheat (Triticum aestivum L.)] and reduced- or no-tillage planting practices on soils that
are relatively low in organic matter and drought-prone. No-tillage systems have been
particularly successful in this region for soil conservation, building soil organic matter,
capturing and retaining soil moisture, and reducing runoff as well as nutrient and
pesticide losses into the Chesapeake Bay watershed. There has been increasing
interest in organic grain production in recent years because of premium prices and
potential environmental benefits to the Chesapeake Bay region. However, there are
challenges in adapting organic approaches to the conventional model of shortrotation, no-tillage grain production because longer rotations are usually
recommended for organic farming and tillage is usually required for seedbed
preparation and weed control.
Two long-term experiments were established at the USDA-ARS Beltsville Agricultural
Research Center in Beltsville, Maryland, to compare the performance of conventional
and organic grain production systems. The Sustainable Agriculture Demonstration
Project (SADP) was initiated in 1994 to compare the sustainability of four reducedtillage cropping systems. The Farming Systems Project (FSP) was established in
1996 to compare three rotation lengths of organic cropping systems with two
conventional systems.
Materials and methods
SADP. The SADP was conducted on a droughty, sloping site in a randomized
complete block with four replicates. Four cropping systems were included in this long-
1
USDA-ARS Sustainable Agricultural Systems Lab, Beltsville, Maryland, USA, E-Mail
john.teasdale@ars.usda.gov, michel.cavigelli@ars.usda.gov
16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/11539
term experiment, but only two will be discussed here: 1) a standard Mid-Atlantic notillage system (NT) with recommended herbicide and nitrogen inputs; and 2) a chisel
plow-based organic system (OR) with cover crops and manure for nutrients and postplanting cultivation for weed control. The NT system followed a two-year maizewheat/double-crop soybean rotation, while OR followed a three-year maize-soybeanwheat rotation. This systems comparison was conducted from 1994 to 2002, followed
by a uniformity trial in which all plots were planted to maize according to the NT
system from 2003 to 2005. Further details of the experimental methods are described
in Teasdale et al. (2007).
FSP. This long-term experiment was conducted on relatively level Coastal Plain soils
in a randomized complete block design with four replicates. The five cropping
systems included: 1) a conventional no-till maize-soybean-wheat/soybean rotation
(NT); 2) a conventional chisel-till maize-soybean-wheat/soybean rotation (CT); 3) a
two-year organic maize-soybean rotation (Org2); 4) a three-year organic maizesoybean-wheat rotation (Org3); and 5) a four- to six-year organic maize-soybeanwheat-hay rotation (Org4+). Hairy vetch and manure were the nutrient sources for
Org2 and Org3, while hay and manure provided nutrients for Org4+. Each phase of
each rotation was included as a split plot in each year. Further details of the
experimental methods and analyses are described in Cavigelli et al. (2008).
Results
FSP. Maize yields at FSP were similar in NT and CT but were lower in the three
organic systems (Figure 1). Among the organic systems, maize yield increased as the
length of rotation increased. Nitrogen availability and weed control exhibited a similar
pattern of response as did maize yield (Figure 1), suggesting that these variables
were important determinants of maize yield (Cavigelli et al. 2008).
FSP Corn
FSP Soybean
a a a
aa
100
b
80
c
d
d
60
c
c
b bc
b
c
40
20
Relative Units
Relative Units
100
a
a
a
a
80
b
b
b
b b
b
60
40
20
0
0
NT
CT
Yield
Org2
Org3
Nitrogen
Weed
Org4+
NT
CT
Org2
Yield
Org3
Org4+
Weed
Figure 1: Average crop yield, nitrogen availability (based on fertilizer rates or
estimated mineralization from organic sources), and weed control at the FSP.
Relative unit of 100 = 10 Mg ha-1 maize grain, 5 Mg ha-1 soybean grain, 170 kg ha1
nitrogen, and 100 % weed control. Bars within variables with the same letter
are not significantly different (P<0.05).
Generally the legumes preceding maize provided insufficient nitrogen and
supplemental manure was limited because manure application rates were
phosphorus-based and this site was high in soil phosphorus. Weed control improved
as organic rotation length increased because there were fewer niches for weed
adaptation in the longer, more phenologically diverse rotations (Teasdale et al. 2004).
16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/11539
An analysis of covariance demonstrated that nitrogen availability accounted for 7075% of the yield differences between organic and conventional systems, while weed
control accounted for 21-25% and maize population for 3-5% (Cavigelli et al. 2008).
FSP full-season soybean grain yields were similar in the two conventional systems
and similar among the three organic systems but higher in the conventional than the
organic systems (Figure 1). Differences in soybean yield were accounted for
exclusively by differences in weed control among systems.
SADP. Maize grain yield averaged over nine years, 1994 to 2002, was 28% lower in
OR than in NT (Teasdale et al. 2007). Reduced yields in OR were accounted for
primarily by competition with weeds. A reduced-tillage approach to weed control was
used for OR whereby a winter annual cover crop (crimson clover before maize) was
flail mowed with the expectation that surface residue would suppress early-season
weeds and that escaped weeds would be controlled by between-row cultivation with a
high-residue cultivator. This approach did not successfully control annual weeds and a
substantial seedbank of broadleaf and grass weeds built up in the soil.
Corn Yield vs. Soil N
9
8
8
Yield (Mg ha-1)
Yield (Mg ha-1)
Corn Yield vs. Soil C
9
7
y = 0.2464x + 3.3303
R2 = 0.6688
6
5
7
6
y = 3.4405x + 2.7455
R2 = 0.7823
5
10
12
14
16
18
Soil C (g kg-1)
20
22
0.8
1.0
1.2
1.4
1.6
1.8
Soil N (g kg-1)
Figure 2: Uniformity trial maize yield (2003 to 2005) as a function of combustible
soil carbon and nitrogen at 0 to 15 cm depth at the conclusion of the SADP
systems comparison (1994 to 2002).
At the conclusion of the SADP systems comparison in 2002, soil carbon and soil
nitrogen were significantly increased in the OR compared to the NT system (Teasdale
et al. 2007). The OR system had supplemental carbon inputs of manure in addition to
plant residue inputs that accounted for higher carbon inputs in this system than in NT.
All plots were planted to maize grown according to NT system operations during a
uniformity trial from 2003 to 2005. Maize grown on plots with a history of OR yielded
18% higher than those with a history of NT during this uniformity trial (Teasdale et al.
2007). Yields in OR and NT during this uniformity trial were highly correlated with 015 cm soil carbon and nitrogen at the conclusion of the experiment (Figure 2). Soil
carbon and nitrogen at 6-12 cm were less correlated with yield (R2 = 0.37 and 0.33,
respectively). Thus, it is likely that yields were higher in plots with a history of OR
rather than NT because of improved soil conditions and nitrogen availability as a result
of increased soil carbon and nitrogen, primarily in the surface 0 to 15 cm of soil.
Higher maize ear leaf nitrogen and higher soil nitrate levels at the maize six-leaf stage
in OR than NT confirmed that there was higher nitrogen availability in the OR system.
16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/11539
Discussion
Organic farming has many of the same goals and benefits for soil improvement as
conventional no-tillage systems. A simulation study of SADP where all systems had
either no or reduced tillage predicted similar annual soil erosion losses among the four
systems (Watkins et al. 2002), while a simulation of FSP based on soil aggregate
distribution showed erosion potential of CT > Org3 > NT (Green et al. 2005). Results
of SADP research showed that soil carbon and nitrogen concentration and maize yield
potential were increased in OR compared to NT, and preliminary data from FSP
shows similar results (Cavigelli, personal communication). This suggests that organic
farming systems with organic amendments can provide greater long-term soil
improvement than conventional no-tillage systems, despite the use of tillage in organic
systems. Manure- and legume-based organic farming systems from nine long-term
experiments across the U.S. also increased soil organic carbon and nitrogen
compared with conventional systems (Marriott and Wander 2006).
This research also demonstrates that the soil-building benefits of organic farming may
not be realized because of the difficulty of controlling weeds in organic systems,
particularly, reduced-tillage organic systems. Additional research is needed to
develop reliable weed management for reduced-tillage organic farming. Advances in
equipment design (The Rodale Institute 2008) have led to improved control of annual
weeds by rolling cover crops to form a dense, tight mat of residue in no-tillage organic
systems. In addition, FSP research (Teasdale et al. 2004) has shown that more
diversified organic systems with perennial hay crops in the rotation maintain a lower
weed seedbank and lower weed abundance than those following simpler grain crop
rotations such as those used in the SADP research. Utilizing rotations with perennial
hay crops would benefit organic systems not only by reducing weed populations but
also by eliminating tillage during a significant portion of the rotation. Therefore, with
inclusion of a perennial crop, the soil-building benefits of no-tillage could be obtained
during the perennial phase of the rotation and the negative consequences of tillage
during the grain crop phase would be minimized.
References
Cavigelli M.A., Teasdale J.R., Conklin A.E. (2008): Long-term agronomic performance of organic
and conventional field crops in the mid-Atlantic region. Agron. J. 100:In press.
Green, V.S., Cavigelli M.A., Dao T.H., Flanagan D.C. (2005): Soil physical properties and
aggregate associated C, N, and P distributions in organic and conventional cropping
systems. Soil Sci. 170:822–831.
Marriott, E.E., Wander M.M. (2006): Total and labile soil organic matter in organic and
conventional farming systems. Soil Sci. Soc. Am. J. 70:950-959.
Teasdale J.R., Coffman, C.B., Mangum R.W. (2007): Potential long-term benefits of no-tillage and
organic cropping systems for grain production and soil improvement. Agron. J. 99:12971305.
Teasdale J.R., Mangum R.W., Radhakrishnan J., Cavigelli M.A. (2004): Weed seedbank dynamics
in three organic farming crop rotations. Agron. J. 96:1429-1435.
The Rodale Institute (2008): The New Farm No-Till + Page, www.newfarm.org/depts/notill/
index.shtml (accessed 2008-02-04).
Watkins K.F., Lu Y.C., Teasdale J.R. (2002): Long-term environmental and economic simulation of
alternative cropping systems in Maryland. J. Sustainable Agric. 20:61-82.