Tomato yields in conventional, low-input and organic systems were not significantly different during the first 17 years. When data from 2009-2011 is analyzed separately, the legume-corn-tomato (LCT) system has higher tomato yields than the conventional or organic systems (the LCT system also receives the highest total nitrogen application rate). Conventional tomato yields were also more variable than organic tomato yields. Part of the reason for low conventional tomato yields in 1999 and 2003 is low soil infiltration. Corn yields, however, were significantly lower in low-input and organic systems. Corn in the conventional corn-tomato (CMT) system is planted earlier than in the organic corn-tomato (OMT) and legume-corn-tomato (LMT) systems, where winter legume cover crops must be incorporated and break down before planting is possible. Up until 2002, shorter season corn varieties were grown in these systems as well. In particular, grain yields have declined, but not biomass yields, which suggests the hypothesis is insufficient N available to corn crops during the grain-filling stage in these systems. To see the data for these yield trends, see the corn and tomato machine-harvested data reports.
Wheat yields were higher in the fertilized systems than unfertilized and legume rotations in both the irrigated and rainfed plots. The irrigated wheat/tomato (CWT) rotation had similar wheat yields to the irrigated wheat/fallow system (IWF). Year-to-year variation is quite high in the wheat system. Fertilized, legume-fertilized and unfertilized systems had similar yearly yield variations, although fertilized yields were higher than unfertilized systems. From 2001 to 2003, wheat yields declined, suggesting that none of the systems were sustainable.
Switching in 2004 to a single resistant variety in both rain-fed and irrigated plots resulted in a return to average or higher wheat yields for all systems. In 2006, California suffered a statewide wheat rust epidemic, which affected yields at Russell Ranch. To see the data for these yield trends, see the wheat machine-harvested data reports.