Organic crops perform up to 100 percent better
in drought and flood years

November 7, 2003: Imagine the press that would be generated if the genetic engineering industry developed a transferable gene that would allow crops to yield 35% to 100% more under drought conditions. Every newspaper would feature the story on its front page and it would be on prime time TV. Well, the organic “industry”, a.k.a. organic farmers and researchers, has done the equivalent, not via genetic engineering, but by developing a soil-plant system that numerous studies have shown gives crop yields that under drought conditions are commonly 100% higher than comparable conventionally managed crop systems.

A paper by Rodale Institute® researchers, published in the September 2003 issue of the American Journal of Alternative Agriculture, describes not only how the organic system gives better yields of corn and soybeans under severe drought conditions, but also shows how the organic system gives better environmental stability under flood conditions, by allowing less runoff and harvesting more water for groundwater recharge.

The paper, “The performance of organic and conventional cropping systems in an extreme climate year”, by Don Lotter, Rita Seidel, and Bill Liebhardt, looked at data from The Rodale Institute’s Farming Systems Trial® (FST) during the climatically unique year 1999. The year was unique because it was characterized by a severe crop season drought, followed by a hurricane-driven torrential rainstorm in mid-September. The results also showed substantial differences between two different organic crop management systems, one based on manure for fertility, and the other based on legume green manure crops.

The Rodale Institute’s Farming Systems Trial has run continuously since 1981 and is one of the longest running crop sustainability comparison experiments in the world. The 1981-2002 phase of the FST (a new phase has recently been initiated) compared corn and soybean crop performance in two organic treatments, one of them manure-based (MNR), and one legume-based (LEG), with a conventional treatment (CNV). The MNR treatment was a five-year corn-soybean-wheat-clover/hay rotation; the LEG a corn-soybean-wheat-green manure rotation; and the CNV a five-year corn-corn-soybean-corn-soybean rotation. Herbicides and synthetic fertilizers were the main inputs into the CNV treatment.

Each replicated plot had a lysimeter underneath the plow layer, essentially a water collecting device, so that water could be collected for a half meter square of each of the 80 foot long plots. Water was pumped out of the lysimeters at intervals and the amount measured. The plots were replicated in such a way that in most years, all three treatments had corn and soybean crops to compare.

The authors start by showing that in five out of six of the drought years during the 21-year experiment, corn yields were significantly higher in the organic treatments than those in the conventional treatment. The 1999 drought year being far more severe, results were more complex, and showed differences between the two organic crop systems.

Rainfall during the 1999 crop season totaled only 41% of average. The critical month of July had only 15 mm of rain, about 17% of the average. Crop yields were reduced to less than 20% in corn and 60% in soybean. Most farmers would have abandoned such a dismal corn crop; however, this kind of stress can expose differences between crop management systems that mild stress conditions cannot.

Yields in 1999 in three out of four cases were at least one third higher in the organic treatments than in the CNV. Corn in the MNR treatment yielded 50% higher than CNV corn, and soybeans in the MNR and LEG treatments yielded 35% and 96% higher than CNV, respectively. The fourth case was the exception: LEG corn yielded 66% lower than CNV corn.

Why did LEG corn fare so poorly – yielding one third of CNV corn, while the other organic treatments in both crops yielded at least one third higher than CNV? This, the authors explain, has to do with the nuanced nature of organic crop management. In the LEG case, hairy vetch, sown in the fall of 1998, grew to near record biomass because conditions in fall and spring were ideal for its growth that year. By the time the vetch was disked under in late April, it had used up what turned out to be most of the water that crops would get that year, which is normally stored in the soil. Additionally, the spring conditions were such that tillage for weed control in the LEG treatment was inadequate, and weed biomass was double that of the MNR treatment. The MNR had a clover cover crop, which had much less biomass and took less water.

Maize and soybean grain yields in conventional (CNV), legume based (LEG) and manure based (MNR) plots, 1999.

The higher yields in the organic treatments are believed to be due to the higher water holding capacity of soils in the organic treatments. Better colonization of roots by beneficial mycorrhizal fungi in organic crops may also play a role, since mycorrhyzae have been shown to help a plant scavenge water from dry soils with their extensive network of hyphae.

Soil water held in the crop root zone was measured and shown to be consistently higher by a statistically significant margin in the organic plots than the conventional plots, due to the higher organic matter content in the organic treated soils.

Water captured below the root zone in the lysimeters provided evidence of the water capture characteristics of the three crop systems. Over a five year period, water collected by the organic plots was about 20% higher than the CNV plots, indicating that groundwater recharge is better in the organic system, and that runoff (and concomitant potential for flooding and erosion) is lower.

The exceptional water capture capability of the organic treatments stood out during the torrential downpours during hurricane Floyd in September of 1999. The organic systems captured about twice as much water as the CNV treatment during that two day event

The authors show a graph of monthly water capture during the 1999 season and point out an interesting fact. In May, when crops were only a few inches high, water “capture” by lysimeters in the CNV plots was one third higher than the organic treatments – the only month in which lysimeter water was higher in the CNV plots than in the organic treatments.

Organic fields capture water better in flood conditions, too.

“Capture” is not the right word for water that percoloates into the lysimeters during a water scarce month, however, because really what was happening, say the authors, is that water was retained by the root-zone soil in the organic treatments, and did not percolate down to the lysimeters. The water retained in the root zone of the organic plots could be used by the crops for growth. Therefore, the true “capture” of water was occurring in the organic plots, and loss was occurring in the CNV treatment. This is offered as additional evidence of the mechanism of drought resistance of the organic treatments – the retention of water in the root zone.

Given that we are entering an era of extreme climate fluctuations and global climate change, the research described here by the Rodale researchers is important. There is great need to develop food production systems that are adapted to climate conditions that are characterized by increased drought and flood. Organic and other crop management strategies that optimize soil organic matter, biological diversity, and crop robustness, should be our first line of defense.

Original research: Lotter, D.W., R. Seidel, and W. Liebhart. 2003. The performance of organic and conventional cropping systems in an extreme climate year. American Journal of Alternative Agriculture 18(3):146–154.