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  • From: "Tradingpost" <tradingpost@gilanet.com>
  • To: livingontheland@lists.ibiblio.org, nmgreens@yahoogroups.com
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  • Subject: [Livingontheland] Organic Outperforms Conventional in Climate Extremes
  • Date: Tue, 13 Jan 2004 04:57:50 -0700


Organic Outperforms Conventional in Climate Extremes
http://www.i-sis.org.uk/OrganicOutperforms.php
The Institute of Science in Society, PO Box 32097, London NW1 OXR

Long-term research has shown that organic cropping systems give higher
yields than conventional during periods of drought or torrential rains. Lim
Li Ching reports.

Sources for this report are available in the ISIS members site. Full details
here

The Rodale Farming Systems Trial was started in 1981 at the Rodale Institute
in Pennsylvania, USA. It compares the benefits and risks of three farming
systems, two organic - manure-based (MNR) and legume-based (LEG) - and one
conventional (CNV), on a long-term basis.

The MNR system is a 5-year maize-soybean-wheat-clover/hay rotation, the LEG
a 3-year maize-soybean-wheat-green manure, and the CNV a 5-year
maize-soybean rotation. The MNR system includes livestock and uses manure as
fertilizer, while LEG incorporates leguminous crops into the soil. Both the
organic systems rely on mechanical cultivation and heterogeneous crop mixes
for their weed and pest control. The CNV system uses mineral fertilizer and
pesticides.

After a transition period of four years, crops grown under the organic
systems yielded as much as and sometimes better than conventional crops.
Average maize and soybean yields were relatively similar in all three
systems over the post-transition years (1985-1998).

Five moderate drought years, with total April-August rainfall less than 350
mm, occurred between 1984 and 1998. In four of them the organic maize
out-yielded the CNV by significant margins. For example, in 1998, organic
maize yielded 141% and 133% relative to CNV in the LEG and MNR treatments,
respectively.

In 1999, a severe crop season drought in the northeastern US was followed by
hurricane-driven torrential rains in September, offering a unique
opportunity to observe how the systems responded to climate-related stress.
As evidence of global warming gathers (see "Life of Gaia" series, SiS 20),
there is greater likelihood of increased incidence and severity of droughts,
flooding and other extreme climatic events. Long-term crop yield stability
and the ability to withstand climatic stresses will be crucially important
for sustainable and secure food production.

The Rodale researchers examined crop and water dynamics by measuring cover
crop and crop biomass, weed biomass, grain yields, percolated water volumes,
soil water content and water infiltration rates.

Crop season rainfall for April, May, June, July and August 1999 were 55%,
66%, 17%, 29% and 40% of normal for those months, respectively. September
1999, with 268%, was a complete reversal of previous months as a result of
Hurricane Floyd, and was the wettest September on record in the Northeast
US.

Due to the severe drought, all crop systems suffered heavy depressions in
yield in 1999: to less than 20% of the long-term average in maize and 60% in
soybean.

There were substantial yield differences between systems. With one exception
(LEG maize), organic systems gave significantly better yields than the
conventional system.

Organic LEG and MNR maize yielded 38% and 137% respectively relative to CNV.
LEG soybean yields were significantly higher than MNR, and MNR in turn
yielded significantly higher than CNV. Organic LEG and MNR soybean yielded
196% and 152% respectively relative to CNV.

The severely reduced yields in the LEG maize plots were largely due to
pressure from weeds and excessive cover crop biomass (nearly twice that
necessary for adequate nitrogen inputs) in that year. Skill in managing
weeds is therefore an important part of organic farming. Both these factors
contributed to over-consumption of the limited soil water, thereby more than
canceling out the benefits of the LEG soil's good water-holding capacity and
infiltration rate.

The primary mechanism thought to be responsible for the higher yields in the
organic systems is indeed the improved water-holding capacity of the soils
during water deficits. Data collected over the past 10 years of the Rodale
research show that the MNR and LEG treatments improve the soils'
water-holding capacity, infiltration rate and water-capture efficiency. LEG
maize soils averaged a 13% higher water content than CNV soils at the same
crop stage, and 7% higher than CNV soils in soybean plots.

In combination, these factors have led to optimum drought adaptiveness in
the MNR maize plots and both the MNR and LEG organic soybean plots. In
contrast, the CNV system had poor soil water-holding capacity and
infiltration, limiting the ability of the crop to adapt to drought despite
negligible water use by weeds and no water use by a cover crop.

Earlier research showed that organic techniques significantly improve soil
quality, as measured by structure, total soil organic matter (a measure of
soil fertility) and biological activity. The improved soil structure created
a better root-zone environment for growing plants and allowed the soil to
better absorb and retain moisture. Apart from the benefit during
low-rainfall periods, it reduced the potential for erosion in severe storms.
The higher organic matter content also made organic soils less compact so
that roots could penetrate more deeply to find moisture.

Furthermore, the organic soils showed good late-season flood performance,
with good water capture and reduced runoff. Water capture is important for
groundwater recharge. Soils in the organic plots captured more water and
retained more of it in the crop root zone than in the CNV treatment in 1999.
Water capture averaged 30% higher in the organic plots than in the CNV
plots, and in September, following high rainfall, water capture in the
organic plots was approximately 100% higher than in CNV plots.

In May, at the onset of drought, the CNV plots, for the only time in 1999,
had more percolated water than the other treatments, indicating that in the
LEG and MNR plots more water was retained in the soil for crop use during a
time when water was limiting. Over a 5-year period, the LEG and MNR systems
captured 16% and 25% more water than the CNV system, respectively. The MNR
plots captured significantly more water than the LEG system.

The Rodale Institute's research provides yet more evidence that organic
agriculture can help ensure sustainable long-term food production (see also
The Case for a GM-Free Sustainable World by the Independent Science
Panel, ). These results highlight the benefits to soil quality organic
farming brings, and its' potential to avert crop failures. "Our trials show
that improving the quality of the soil through organic practices can mean
the difference between a harvest or hardship in times of drought", said Jeff
Moyer, Farm Manager at Rodale Institute.

Given the increasing incidences of climate extremes, and projections that
these are likely to occur more frequently, organic crop management
techniques will be important in providing soil and crop characteristics that
can better buffer environmental extremes.










  • [Livingontheland] Organic Outperforms Conventional in Climate Extremes, Tradingpost, 01/13/2004

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