Cultural Measures, Crop Protection and Economics in Cereal Monocultures in Bavaria¹

Abstract

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. Summary 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 barle...

Cyst‐forming Nematodes on Cereals in Bulgaria1

“…Many authors have investigated the population dynamics of H. avenae in relation to cereal crop rotations or cereal monoculture, but the results obtained have been contradictory in many cases. Many cases are known when, after a prolonged monoculture of cereals, the nematode population increases or, on the contrary, decreases or is sustained at a comparatively low level below the damage threshold (Gair et al, 1969 ;Diercks, 1975). One cause of this last phenomenon has been shown to be the appearance of fungi on the females, eggs and larvae (Kerry & Crump,197?…”