Yield differences and trends, organic matter accumulation, and the loss of nutrients to deeper soil horizons are discussed using data from organic and conventional maize/tomato cropping systems from the Long Term Research on Agricultural Systems Project (LTRAS) at the University of California, Davis. Compared to the conventional system, higher and increasing yields of tomatoes were observed in organic systems, but lower yields of maize. Fruit quality, measured as soluble solids, was not significantly different. Soil organic matter increased in the organic system, but remained stable in the conventional one. More irrigation water was used in the organic system than in the conventional one due to higher rates of infiltration, but less winter runoff occurred during the rainy season for the same reason. There was no measurable loss of inorganic N (NO3, NH4) in soil to 3 m depth in either the conventional or organic system after ten years of farming
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