Do organic systems produce sufficient yield?

Organically grown crops do not reach the crop yield level of conventional systems that are minerally fertilized and protected by synthetic chemicals. An average crop yield reduction of 20 percent has to be accepted.

Considering that the input of fertilizers was almost 50 percent lower in the organic systems, the average yield reduction of 20 percent appears to be reasonable. Moreover, organic systems avoid the use of synthetic fertilizers and pesticides that are produced with fossil energy and at high environmental costs. Crop yield in the organic plots was in fact higher than expected. Nutrients in the soil appear to be utilised to a higher extent as supported by root symbioses with rhizobia and mycorrhizae.

Potato tuber yield reduction was most severe compared to the conventional system and may be explained by a high plant demand for nutrients in a relatively short vegetation period, in addition to the high susceptibility of this crop to pests and diseases.

Due to the appropriate choice of crop rotation and mechanical control, weeds never competed significantly with the crop plant. The possibility for direct plant disease and pest control, as well as application of soluble fertilizers, resulted in the conventional systems in a slightly enhanced crop yield stability.

The following years will show if the organic systems will be able to compensate for the lower soil nutrient loads by an enhanced soil fertility.

Winter wheat, grain yield

Winter wheat yield was 11 to 14 percent lower under organic conditions than in the conventional systems. In the first crop rotation period the yield appeared to be comparable. Thereafter, improved management and better varieties led to higher crop yield in all systems.

Potato tuber yield

Potato yield in the organic systems was 34 to 42 percent lower than with conventional treatments. This was observed already in the first years after conversion. In addition to lower tuber yield, a greater proportion of small tuber classes reduce the marketable yield, as did the increased damage due to wireworms.

Grass clover yield in the first two ley years

The differences in the yield of the first two years of the grass clover ley were comparably low, with 11–13 percent less. During the third crop rotation period the yield difference increased, possibly due to the changed grass-clover mixture and the slightly lowered manure rates. The slight difference between the two organic systems in the third crop rotation period may be caused by the increased potassium fertilization in the bio-dynamic system.