Published Sep 24, 2012

Webinar Review: “Keys to Agricultural Sustainability and Resilience: A Scientist’s Perspective”

By Margaret Chamas

September 19 2012


The Iowa Learning Farms holds a webinar on the third Wednesday of each month, and this time featured ISU professor of agronomy Matt Liebman.  The talk focused on potential environmental threats from some common agricultural practices, and some research work Liebman has been involved in to alleviate some of those issues.

Liebman started by addressing the definitions at hand: what exactly is implied by a sustainable or resilient practice?  Sustainable activities are those that conserve resources (physical/environmental, as well as fiscal) and prevent pollution or degradation of the environment.  Resilient practices are those that, when presented with shocks (like pests, volatile weather, or sudden price changes), are able to continue functioning without failing.  The two concepts are different, but both desirable, and both require diversity to be truly present.

Iowa’s current agricultural situation is one of “simplicity and homogenization.”  About 63% of the state’s surface area is covered by corn or soybeans; another approximately 20% is in some other variety of crops.  This leaves little ability to rebound from challenges to the production or marketing of these crops.  While the concentration of these products has benefited the crop growers and made it possible for other enterprises (livestock, ethanol) to function, it has also degraded environmental quality.  Many areas in Iowa contribute 1800-3000 kg of nitrogen per acre into runoff water.  While a cornfield might lose 45-50 lb N per year, an acre of alfalfa or grassland will only lose 1 or 2.

Herbicides are another environmental danger.  Some, including atrazine, have demonstrated negative effects on wildlife and potentially on humans.  Liebman cited information that over 90% of tested agricultural streams were positive for atrazine, and many were at levels that exceeded the MCL (maximum contaminant level).  As if this weren’t challenge enough, many weed types are becoming resistant to herbicides, notably glyphosate.  Scientists are now looking to add more resistance traits to field crops…which will increase use of these other chemicals, which could then also end up in runoff.  At the same time, the resistance issue is not likely to go away, and will probably become worse as those resistance traits get stacked not just in the crops, but through selection also become common in the weeds.

Liebman’s work has dealt with finding systems that diversify corn and soy-based rotations with small grains and forage crops.  He has looked at the economics of the rotations, as well as the effects on herbicide resistance and chemical dependency.

One trial tested three systems: a conventional two year rotation (corn/soy); a three year rotation (corn/soy/oats), and a four year rotation (corn/soy/oats/alfalfa).  The two-year rotation was managed similarly to many farms: Bt corn and roundup-ready soybeans were planted and 100 lb N was banded at planting; additional fertilizer and herbicides were applied later.  The three- and four-year rotations used non-transgenic crop varieties, and fertilizer was only applied according to soil test recommendations – though manure was applied when the fields were bare.  Weed control was done mainly by cultivation, harvesting the oats, some banded herbicides, and stubble clipping.  The results showed a reduction in use of N fertilizer and banded herbicides by at least 90%, when comparing the three- and four-year rotations to the two-year rotation.  The longer rotations also yielded more corn and soybeans per acre than did the conventional system.  They required more labor, but offered savings on fuel consumption per acre.  The revenue per year, averaged over the entire rotation (so taking into account the years of oats and/or hay production), were no different between systems.  Liebman and the other researchers concluded that diversification of rotations like this consumed less fossil fuel but required more labor, while maintaining equal profits.  He also reported somewhat greater weed biomass on the longer rotations.  Interestingly, the crops on the longer rotations also seemed stronger: despite bouts of sudden death syndrome in 2010, the longer rotation crops did not suffer yield decreases like the two-year rotation crops did.

The next piece of work Liebman discussed dealt with the amount of water and particulate matter running off of agricultural fields.  Some experts predict years of widely variable and very extreme weather and precipitation events, which could compound the loss of water and soil from fields already present.  For instance, the floods of 2008 caused an estimated loss of 20 tons of soil per acre on large areas of farmland.  Liebman’s team sought to stabilize soil and water systems through the use of buffer strips of restored prairie.  Prairies species, he noted, tend to remain upright even when faced with heavy rainfall – thus they trap more water than cool-season grass strips alone.  Sloped watersheds in the Neal Smith Wildlife Refuge were put into one of four treatments: no buffer strips, 10% of the area in buffer strips at the bottom of the slope, or 10 or 20% in two or three buffer strips both at the slope bottom and further uphill.  The amount of water and type and amount of contaminants were evaluated.  Buffer strips reduced the amount of sediment in the runoff by approximately 95%.  Even in years with extreme rainfall events (2008 and 2010), the reduction in particulate runoff remained the same.

In addition to demonstrating the potential to reduce chemical dependency and pollution through diverse crop systems and buffer strips, Liebman presented information about the implementation of these practices.  Does the public want legislation or management systems in place to ensure that these systems are enacted?  Would people be willing to pay taxes or fees so that farmers could be assisted in implementation?  A survey he cited found that improvement of water quality was one of the top ten concerns and priorities that people had for agriculture.  Overall, participants were willing to pay an average $33 per year towards programs to get these practices in place.  Across all of Iowa, that would mean $42 million – certainly enough to help conserve some soil.  A cost analysis Liebman mentioned also found that installing prairie strips is quite cost-competitive with other types of riparian buffers and terracing, while being more environmentally beneficial.

In the subsequent question and answer period, Liebman was asked how to actually get these changes in place.  He stressed the importance of livestock integration, particularly in longer-rotation systems like the first trial worked with.  Animals can make use of both the oat and alfalfa rotations, and in turn would provide the manure used to fertilize the fields.  In addition, adding a cost-share program to ease the loss of revenue in the non-corn/soy years would be good; development of a small-grains market or adding incentives were other possibilities.  A few questions focused on the long-term profitability of the longer rotations.  Liebman stated that he expected them to remain profitable, particularly if there was any federal assistance during the small-grains years.  He noted that the variability of yield in the long-rotation corn and soy years was low: they consistently produced more than the conventional.  Similarly, while he acknowledged that the high prices of corn and soy made the two-year rotation very tempting, the cost of inputs for those crops keeps rising as well.  The longer rotations offer a reduction in those costs.  At moderate corn and soy sale and input prices, the three-year rotation becomes quite attractive.

Iowa agriculture faces environmental, political, and financial challenges.  According to Iowa State’s Matt Liebman, a good solution is diversifying crop rotations and implementing conservation practices, to make systems more sustainable and resilient.  His research work demonstrates methods of adding fewer chemicals to the soil, diversifying rotations, and retaining soil and water – while also maintaining yields and profitability.  While some of the changes might seem a huge shift for agriculture, they seem small in comparison to the absolute desolation that could come with too many more years of floods or droughts.

The webinar, along with other previous sessions, can be accessed at