Two organic and a conventional (integrated) agricultural systems have been compared in a randomized plot experiment (DOC trial) at Therwil (Switzerland) since 1978. DOC stands for bio-Dynamic, bio-Organic and Conventional agriculture. These three systems are performed at two fertilization intensities. The systems differ mainly with respect to fertilization and plant protection strategy. One additional conventional system was unfertilized in the first crop rotation period but since then, it has been exclusively fertilized with mineral nutrients. One system remains unfertilized. Crop rotation (potatoes, winter wheat, beetroots, winter wheat and three years of grass-clover) and soil tillage are identical in all systems. Three different crops are grown in four replicates each year.
Nutrient input to the organic treatments was 40-60 percent lower than to the conventional system, with respect to nitrate, ammonia, phosphorus and potassium.
During the first years, yields of winter wheat did not differ between the systems. Differences between the systems increased in the second rotation period with a new variety and enhanced pesticide management in the conventional systems. Between 1985 and 1995 winter wheat yields in the conventional system were higher than in the two organic systems. In the years 1996 and 1997 winter wheat yields were almost identical in all three systems.
On average, the yield from all crops in both organic systems was 20 percent lower than in the conventional systems, mainly as a result of the lower nutrient input. System effects on crop yield were most obvious with potatoes, mainly due to the high demand for nitrogen and potassium, which are not adequately available in the organic soils during the short vegetation period of potatoes. Differences in grass-clover yield were comparably low during the first two crop rotation periods. In the third crop rotation period, however, grass-clover yield in the organic systems was distinctly lower than in the conventional systems.
Even though yield for all crops was lower in the organic systems, energy use per unit crop yield was 18-33 percent lower than in the conventional system, except for potatoes. This difference was mainly due to indirect components of energy, i.e. the energy used for production of machinery, pesticides and Fertilizers.
Alföldi T., Mäder P., Besson J.-M. and U. Niggli (1995): "DOC-trial: Long-term effects of bio-dynamic, bio-organic and conventional farming systems on soil conditions, yield and product quality", ed. J. Raupp, Main effects of various organic and mineral fertilization on soil organic matter turnover and plant growth, Darmstadt, 3-15 pp.
Besson J.-M., Spiess E. and U. Niggli (1995): "N uptake in relation to N application during two crop rotations in DOC field trial", Biol. Agricult. Hortic. 11, 69-75 pp.
Mäder P., Alföldi T., Fließbach A., Pfiffner L. and U. Niggli (in press): "Agricultural and Ecological Performance of Cropping Systems Compared in a Long-term Field Trial". In: Nutrient Cycles and Nutrient Budgets in Global Agro-ecosystems, ed. E. Smaling, CAB, London.
Mäder P., Alföldi T., Niggli U., Besson J.-M. and D. Dubois (1997): Der Wert des DOK-Versuches unter den Aspekten moderner agrarwissenschaftlicher Forschung. Archiv für Acker-, Pflanzenbau und Bodenkunde 42: 279-301 pp.
Siegrist S., Schaub D., Pfiffner L. and P. Mäder (1998): "Does organic agriculture reduce soil erodibility? The results of a long-term field study on loess in Switzerland", Agric. Ecosys. Environ. 69: 253-264 pp.