May 16, 2011 | Jeremy Ogul

Most agricultural experiments last anywhere from a few months to a few years, but at Russell Ranch near Davis, CA, researchers are in the midst of a 100-year study measuring the sustainability of various farming systems.

The study, known as Long-Term Research on Agricultural Systems (LTRAS), is designed to measure the long-term impact of different cropping systems, irrigation practices, tillage methods and carbon and nitrogen inputs on agricultural sustainability. It was started with a grant from the Sustainable Agriculture Research and Education Program in 1990.

Emma Torbert, a post-graduate fellow at the Agricultural Sustainability Institute (ASI) at UC Davis, which manages LTRAS, said a 100-year study is the best way to determine the sustainability of different farming practices.

“Sustainability is a long-term question and you need long-term experiments to know if farming practices are sustainable,” Torbert said. She pointed to Rothamsted, a long-term agricultural experiment in England that began in 1843. It took 80 years before acidity buildup in the soil resulted in the growth of a fungus that decreased turnip yields.

But it takes more than time to determine what’s sustainable. You also need to have a clear sense of what sustainability means. “Sustainable ag must be profitable, environmentally sustainable, and produce healthy food under reasonable labor conditions for it to truly sustain everyone from the farmer to the laborer to the consumer to the neighbor downstream,” Torbert said.

LTRAS researchers use a variety of long-term metrics to measure whether different farming practices meet those sustainability criteria. LTRAS researchers monitor long-term trends in yield, soil carbon and nitrogen levels, microbial biodiversity in the soil, greenhouse gas emissions, water use, nutritional content of the food produced and weed populations. They also measure long-term trends in profitability by monitoring the cost and efficient use of inputs such as fuel, herbicides and pesticides, water and labor.

The Study Design

On 57 plots, arranged over 300 acres, ten different cropping systems on two-year rotations have been structured around a gradient of increasing fertilization and irrigation intensity. The systems, which utilize different combinations of organic, conventional, irrigated, rainfed and no-input farming practices, include corn/tomato, wheat/tomato, wheat/fallow and wheat/legume rotations. In addition to the larger long-term plots, there are micro-plots that allow scientists to test hypotheses on a short-term, smaller-scale basis.

Research Findings from LTRAS (1994 – 2008)

Even within a short window of 14 years, important findings have emerged. Here are some of the highlights:

• Higher carbon inputs – using compost and planting cover crops in the off-season – have led to higher soil carbon levels. Soil carbon matters because it’s linked to many beneficial soil properties, Torbert said. “It can improve water holding capacity for the soil, and it’s linked to improving soil structure. Better soil structure for plant roots can lead to decreased disease.”

• Cover cropping systems have increased water infiltration in the soil, which, in turn, has reduced runoff. Cover crops used in the study include oats and vetches, which are planted in November and are rain-fed through the winter months.

• Reduced soil tillage substantially reduced fuel use, but with a tradeoff: in soils with low levels of organic matter, reducing tillage led to sealing of pores in the soil, which increased water runoff.

• Food quality investigations have shown that flavanoid concentrations in organically grown tomatoes were significantly higher than in conventionally grown tomatoes. Flavanoids are secondary metabolites found in plants; there is some evidence that they may help prevent cardiovascular and other diseases in humans.

• Tomato yields were similar across conventional, low-input and organic systems.

• Corn yields were significantly lower in organic and hybrid systems than they were in the conventional systems.