LTRAS

Long Term Research on Agricultural Systems

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Click on the image to enlarge, or download the pdf here.

The Century Experiment (LTRAS) is located on the main plots at the Russell Ranch Sustainable Agriculture Facility. LTRAS measures the long-term impacts of crop rotation, farming systems and inputs of water and nitrogen on agricultural sustainability. The cropping systems in the long-term experiment include rainfed and irrigated systems, organic and conventional systems, and different forms and quantity of nitrogen inputs. The LTRAS study began in 1993 with a uniform sudangrass crop to evaluate inherent soil differences and the original cropping systems were first planted in 1994.

Current experimental design

 

The cropping systems at the Century Experiment are designed to fall along a gradient of increasing irrigation and fertilization intensity. Currently, the Century Experiment contains ten systems that are two-year rotations and include corn/tomato, wheat/tomato, wheat/fallow and wheat/legume rotations. Additionally, a perennial native grass system and a 6-year alfalfa-corn-tomato rotation were initiated in 2012. There are six one-acre plots per system, three plots for each of the two phases. Each plot also contains 40 micro-plots which allow scientists to test hypotheses on a short-term basis. These micro-plots are outside of the yield measuring area, which is used for long-term data collection.

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Changes in cropping systems

 

The cropping systems of the long-term project are being evaluated to be more flexible and responsive to current trends, while maintaining the integrity of the long-term experiment. Long-term experiments are dynamic and need to respond to changing farming practices, as well as address evolving scientific priorities. Additional new projects being discussed include: integrated nutrient management systems, animal forage systems, woody perennials (orchards and vineyards), reduced tillage rotations and restoration ecology.

Original Experimental Design 

 
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 Changes in cropping systems since 1993:

  • In 1999, a new transitional system (indicated by **) was added which converted conventional plots to an organic corn/tomato rotation (see Elizabeth Martini's paper here)
  • In 2003, SAFS moved to the Century Experiment. The Legume-Corn-Tomato system was altered to receive cover crop each winter (instead of every other winter).
  • From 2003-2007, all one-acre plots of the tomato/corn systems were split in half and reduced tillage treatments were compared to standard tillage treatments (see tillage results here)
  • In 2007, Irrigated Wheat/Legume was discontinued (indicated by †)
  • Wheat replaced corn from 2010-2012 (indicated by a * in the current cropping system table)
  • In 2012, two systems, a six-year rotation (alfalfa-tomato-corn) and perennial native grasses, were added to the Century Experiment