Cultural Measures, Crop Protection and Economics in Cereal Monocultures in Bavaria1
Authors: Diercks R. 
Published: April 2008

Experience and long‐term experiments in Bavaria demonstrate that the question of cereal monoculture should be considered from 3 different points of view: that of plant protection, plant cultivation and economics. Thus, continuous cultivation of spring barley is possible without increasing the risk of crop failure, but must be rejected on economical grounds when spring barley is the only marketable product, because of low returns. Continuous cultivation of economically more interesting crops like wheat is limited by pathogens which, however, fluctuate greatly according to location, year and virulence. A decrease in yield of up to 20% may be expected in the most unfavourable circumstances. Various developments in the field of production technology allow to prevent losses to a certain extent or to compensate for them by increasing the yield accordingly. However, even so the yield obtained in extensively used crop rotations is seldom matched by production techniques in monocultures. Since the benefit resulting from the rationalization does not compensate for the loss of income, it is not practicable at this stage to think in terms of wheat as a monoculture in the absence of other marketable commodities on the farm.

The percentage of cereals on arable land can be increased up to about 75%, even when limited to wheat and barley, and without jeopardizing the yield and accordingly the returns. If the farm organization completely excludes the labour‐demanding root crops, i.e. sugar‐beet and potatoes, these can be replaced by the so‐called combine harvest crop rotations, including mainly grain maize and rape seed. Combine harvest crop rotations offer an extended choice of crops and are labour‐saving; they secure high returns without endangering the soil equilibrium.

The problem whether traditional crop rotation should be replaced by cereal monocultures on the grounds of economic incentives encouraged studies along these lines since 1968. At this stage an interim report on the results can be summarized as follows:

1) The cultivation of winter wheat, as a monoculture or alternating with spring barley, is limited by pathogens which can cause yield depletion according to location, soil and other factors; under unfavourable circumstances the losses can thus reach 20%. These losses can be compensated to some extent either by cultural or plant protection measures or indirectly by increasing the capability of the plant to recover. However, the yield obtained in extensively used crop rotations is seldom reached by monocultures. Since the profit from rationalization does not compensate for the loss of income, it is not yet practicable to think in terms of wheat as a monoculture. This is true even if wheat is the only marketable product of the farm (main income farms are especially considered here), also because farms in Bavaria are mostly smaller than 50 ha. It is also important to note that the losses did not increase over the years but that a stabilization occurred with the time.

2) A monoculture of spring barley would be possible without jeopardizing the yield, but must be rejected on economic grounds because the price of this commodity is too low to secure an adequate income if this is the only marketable crop.

3) The percentage of cereal crops can be increased up to 75% without endangering the yield and without reducing the farm income, even when the crop is limited to wheat and barley. If the farm organization is to be extended according to a work program which completely excludes the labour‐demanding root crops (sugar‐beet, potatoes), they can be replaced by the combine harvest crop rotations including grain maize, rape seed, field beans, and grass seed production. Combine harvest crop rotations offer a pallet of many species, are labour‐saving, economic and are considered as sound crop rotations in the classical sense.

4) Generalizations on the impact of green manuring in the field of plant protection are impossible since there are too many parameters involved. A multidisciplinary assessment of the joint effect of crop rotation, methods of production, soil, ecological data and weather conditions could lead the way. When monoculturing winter wheat, a bad harvest might be attributed to a lack of moisture during a dry autumn and to the inadequate consistency of the soil rather than to insufficient crop protection.

5) In spring barley monoculture, growing resistant varieties is beneficial in the presence of the cereal cyst eelworm H. avenue; heavy losses can thus be prevented.