Basics of Renewable Energy Supply - Renewable Energy: Technology, Economics and Environment - page 87

Plant cultivation measures. Together with the factors set by the natural location
such as temperature of precipitation, an anthropogenic influence on plant growth
through plant cultivation measures is possible. These measures can be choosing
crops suitable for the individual conditions of the site, the cultivation of the soil,
the sowing method, fertilisation, plant husbandry, and harvesting measures. The
plant cultivation production technique should support the realisation of the respec-
tive yield potential of a plant in a particular location.
The main requirement is the selection of a plant type adapted to the ecological
and environmental conditions of the production site. This affects the demands
towards the condition of the soil as much as the amount of precipitation and its
distribution, the temperature and the temperature distribution curve within the
year. Soil cultivation is performed to loosen the soil, to mix remaining crop resi-
dues as well as mineral and organic fertilisers (i.e. animal manure) into the soil, to
fight weeds, to prepare the soil for sowing and to sow or to plant young plants.
Timing and technique of soil cultivation have to be adjusted to the soil condition
(e.g. wetness of the soil) and the requirements of the plants.
Crop rotation determines the timely sequence of crops in a field. It is limited by
biological factors, as the cultivation of the same or related crops in consecutive
years is limited by diseases. Consequently, some crops cannot be produced year
after year on the same field. Crop rotation has to be planned in a way that leaves
enough time for preparing the soil between harvesting one crop and sowing the
next. Therefore crops with early sowing times, such as winter rape and winter
barley, cannot be cultivated in the same field that was used to produce late-harvest
crops such as maize or sugar beets.
Fertilisation measures are aimed to directly improve the nutrient supply of the
plants (e.g. mineral nitrogen fertiliser) and the properties of the soil (e.g. lime
treatment or addition of organic substances). The level of fertilising depends on
the amount of nutrients withdrawn from the soil by the plants. The strongest influ-
ence on the yield is achieved with nitrogen fertilising, as the nitrogen supply in
the ground is mostly a limiting factor for yield, and nitrogen mainly supports mass
growth. Nitrogen is mainly added to soil in the form of mineral or organic fertil-
iser, by nitrogen fixation of leguminous plants (i.e. clover), or through rain from
the air (i.e. the nitrogen released from anthropogenic sources mainly as NO x is
deposited partly also on agricultural land and acts here as a nitrogen fertilizer).
Together with nitrogen, fertilising with phosphorus and potassium is normally
also carried out on a regular basis. In addition to its function as a plant nutrient,
potassium is also important for the fertility of the soil. It influences the pH-value
of the soil and thus its chemical reactions and the availability of various nutrients,
and stabilizes the structure of the soil with its bridging role. Apart from magne-
sium, which can often be found in potassium fertilisers, all further nutrients are in
most cases sufficiently available in the soil and are only applied in the event of an
obvious deficiency.
Crop protection measures during the vegetation period serve to prevent or fight
weeds, diseases and pests. Weeds compete with the crops for growth factors, thus