Increased Crop System Diversity: an Alternative to Prolific Pesticide Use

While doing the research for the GMO series I stumbled across a fascinating, long-term study closer to the scale of Rural System. The authors hypothesized that diverse, 3 and 4-year crop rotation systems would provide ecosystem services, “that would supplement, and eventually displace, synthetic external inputs used to maintain crop productivity.” Upon examining their results, I would say that not only does this seem to be the case, but such systems would likely create jobs as well. Diverse crop rotations, if effective at suppressing weed populations, would be an attractive alternative to GM crops designed to withstand intensive herbicide application. The results of this study would also be particularly interesting to organic farmers, who are already limited in their selection of pest control methods.

crop rotation diversity

Aerial view of Marsden Farm study, Boone IA. Crop abbreviations: m = maize, sb = soybean, g = small grain, a = alfalfa.
Provided thanks to a Creative Commons CC0 public domain dedication.

The study took place between 2003 and 2011 in Iowa with three plots close in proximity and in soil quality. The experiment covered a total of 9 hectares. On the year preceding the study, the entire experimental area was planted with oat. The plots were 18m x 85m, “using a randomized complete block design with each crop phase of each rotation system present every year in four replicate blocks.”

  • One treatment was a conventional 2-year rotation of corn and soybean crops, receiving agrichemical rates comparable to those used in surrounding farms of the region.
  • One treatment was a 3-year rotation of corn, soybean, a small grain (alfalfa or oats) with red clover green manure.
  • The remaining treatment was a 4-year rotation of corn, soybean, a small grain, and alfalfa hay managed with reduce N fertilizer and herbicide inputs.

Remarkably, all three treatments performed similarly on yield, profit, and weed suppression.

“Two lines of evidence indicate that weeds were managed effectively in all three cropping systems in both the ‘startup’ and ‘established’ phases, in spite of reducing herbicide use by 88% in the 3-yr and 4-yr rotations compared to the 2-yr rotation. First, weed seedbanks declined at an equal rate in all study systems…. The second line of evidence concerns weed biomass, which was very low in all three cropping systems for the duration of the study, never exceeding 0.3% of harvested crop mass.” –Davis et al.

The conventional 2-year rotation approach required much higher inputs of synthetic fertilizer and insecticide, with greater freshwater toxicity and energy use. The 3 and 4-year rotation approaches reduced all of these, but required more labor input.

Performance of Diverse Crop Rotation Systems

Here you can see the performance of three crop rotation treatments in yield, profit, synthetic inputs, etc.
Provided thanks to a Creative Commons CC0 public domain dedication.

It is also encouraging and interesting that the 3 and 4-year rotation systems had less variance in profits over time, supporting Rural System’s notion that diverse systems make for stable, sustained profits.

Lastly, the results of this study indicate that the 3 and 4-year systems with reduced agrichemical applications decrease overall toxicity to neighboring ecosystems.

“Environmental toxicity, in relation to ecotoxicological profiles for herbicides used in this study (Fig. 2c), showed a strong effect of system (F2,14 = 1673, P<0.0001), with lower toxicity potential in the 3-yr and 4-yr rotations compared to the 2-yr rotation (type: F1,17 = 2691, P<0.0001). Ecotoxicity in the diversified and conventional systems diverged as the systems matured over time [type x phase: F1,16 = 7.4, P = 0.015], transitioning from a two-fold difference during 2003 to 2005 to a two hundred-fold difference in toxicity from 2006 to 2011 (Fig. 2c).”

Rural System continues to assert that an increase in system diversity allows for a decrease in synthetic inputs, and a corresponding increase in land health. The study summarized above suggests that the current petrochemical-intensive and herbicide-intensive agricultural practices do not increase yield and profits above those of a more diverse, but labor-intensive approach. Modern agriculture has focused on labor-saving technology.

Should we be “saving labor” with thousands of people unemployed? Perhaps it is time to move to ecologically sound, diverse rotation systems combining crops with livestock to decrease inputs, increase profits, and create jobs.

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About Laurel Sindewald

Laurel is an alumna of Warren Wilson College with a BS in Conservation Biology and a BA in Philosophy. She is a writer for Rural System, Inc.

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