Long-Term Research in Irrigated and Dry Land Agriculture: Crop Yields and Soil Properties.

The Century Experiment at Russell Ranch, a long-term experiment at UC Davis was established in 1993 to measure the sustainability of different cropping systems, including properties such as crop yields and crop quality, carbon sequestration, and resource use efficiency. The cropping systems in the Century Experiment include conventional, organic and a mixed (conventional with cover crop) tomato-corn rotations, a 6 year alfalfa-corn-tomato rotation, as well as wheat rotations varying from no fertilizer to full fertilizer and rainfed to supplemental irrigation. The cover-cropped conventional system had significantly higher tomato yields for the last 5 years, as compared to the organic system and the conventional system without cover crops. The conventional corn-tomato system had significantly higher corn yields, but not significantly different tomato yields, as compared to the organic corn-tomato system. The fertilized wheat yields have been significantly higher than the unfertilized treatments over the last 21 years, and the supplementally irrigated wheat has had significantly higher yields as compared to the rainfed wheat. The organic corn-tomato systems had increased soil carbon sequestration and soil microbial biomass as compared to the conventional and cover-cropped conventional systems, as well as increased sequestered soil potassium and phosphorus. From 1994 to 2004, the concentration of flavonoids, plant secondary metabolites and anti-oxidant compounds potentially related to reduction of cardiovascular diseases and obesity, were significantly higher in organic as compared to the conventional tomatoes.