Cup-plants are herbaceous perennials; they resprout every year and the number of their flower shoots is increasing continuously. The solid, perennial plants show 20 to 35 stems maximum per square meter. Cup-plant or Silphium-fields need to be planted only once. Afterwards they can be used for 20 years or longer. Thus many worksteps in the field – as compared to maize - can be omitted. Whereas the cultivation of annual crops has to be prepared (purchase of seeds, ploughing, grubbing, sowing etc.) and regularly treated with pesticides, cup-plant crops need these preparations only in the first year.
The only remaining field work is:
- fertilization in March before sprouting
- harvest in September with commercially available maize chopper
Since so far no pests are known for Silphium, there is no need of pest management after the first year. During the first year weeds have to be removed: either mechanically with hoeing machines or with herbicides (for this measure a special permit according to § 22 PflSchG is required).
Die Cup-plants grow up to 2,20 m high or higher. The yield varies with soil quality, water availability and fertilization. With fertilization of 130-150 kg N per ha, 120-200 dt/ha dry matter are gained. Since the plants do not have a spadix rich in starch like maize, their methane yield is about 10 % lower than that of silo maize.
The fine roots of cup-plants are permanently found in depths of 2 m. Thus they are able to use all applied fertilizer for growth. Heavy rainfall in spring and summer is not able to shift the fertilizer into depths that cannot be reached by the plant roots. Exploitation rates, therefore, are practically 100 %. As a consequence, cup-plant cultivation can also be recommended in catchment areas.
Cup-plant flowers develop by end of July until mid-September. They are visited by numerous insects and especially by honeybees for pollen and nectar. Since during that time period no honey yield can be found elsewhere, the flowers of cup plants provide an additional source for pollen and nectar for bee colonies, but also for many other insects.
The still ongoing increase of wild pig populations throughout Germany is caused – according to the unanimous opinion of experts – for the most part by the increasing cultivation of maize, which provides them with a nearly unlimited food source. Wild pigs are responsible for massive damages in maize and other agricultural crops. With increasing wild pig populations there is also a higher risk of swine fever. Additionally, a rising number of traffic accidents caused by wild pigs is reported by the police. Maize stems turned down by wild pigs have to be eliminated from the field before growing the following crop (which is an additional investment). If they were left on the field and ploughed in, the wild pigs would tear them out again later, causing more damage in the crop that follows. Cup-plants are not eaten by wild pigs. Installing more cup-plant fields instead of maize would, therefore, reduce the expansion of wild pigs.
- Improvement of soil quality by humus accumulation and regeneration of soil organisms (earthworms)
- No food source for wild pigs
- Reduced erosion and risk of floodwaters
- No soil compaction
- No production of poisonous silage saps
- No acid cleaning of seeds
- No pesticides after the first year
- No annual purchase of seeds
- No re-seeding fees
- Less use of soil treatment machines
- High resistance against drought (on deep soils) and severe winter frost
- After severe storms the fallen Silphium-stems may be left on the field. They do not obstruct the new shoots in spring and do not have to be removed like maize stems.
- Cup-plants tolerate light frost up to -3 oC. Thus they are less vulnerable to early or late frosts than maize.
- Cover for small game starting from april
- If cup-plant stands are harvested before mid-September, the root stock builds new rosette leaves before the first snowfall. These provide good cover for small game on the agricultural fields in fall (cover from wind, cold, rain, predators).
- The cultivation of cup-plants reduces risks in years of unfavourable weather conditions for maize (like wet and cold spring, summer drought). Additionally Silphium-crops may be harvested over a relatively long period, which attenuates work peaks.
- By the limitation of silo maize as digestate to 60 % of the used biomass through EEG (so-called „Maisdeckel“; since January 1, 2012) other raw materials gain importance for fermentation: by the biomass regulation in the EEG the fermentation of Silphium is promoted; the refund per supplied kilowatt hour is increased proportionately for electricity produced by materials of enclosure 3 (Einsatzstoffvergütungsklasse II; thus also for Silphium) by 2 cents/kWh. This means a surplus of ca. 250-300 Euros per hectare and year!
- An actual comparison of production cost of maize/cup-plant for the biogas production is available for download here: Comparison of costs of production Maize vs. Cup-plant
- Long use of etablished stands (high saving potentials)
- The stand is an adding value; thus there is a monetary gain in case of changing the status of lease of land.
- Possibility of immediate use of the stand in case of new lease of land (no investment costs, no waiting time, everything is prepared, only fertilization and harvest necessary).
Regarding the primary investment, cultivation of cup-plants is only profitable if the crop can be grown for more than five years. Cultivaton for 12-15 years or more is preferable . Because of the slow juvenile growth and high competition by weeds on arable fields, it is recommended to plant pre-cultivated seedlings. Direct sowing is a problem, since selective herbicides are not yet available in order to keep down weeds from the beginning. Cup-plants need deep soils with good water supplies. On sandy soils, harvests will be less extensive in dry years (dessication of leaves and shoot tips). In these years, the crop should be harvested earlier than September. In the year of planting the crop is not harvested but will wilt with the first frosts and build a herbaceous cover that prevents erosion.
Silphium as a wild species, which has not yet been exposed to breeding, shows - like most wild species - only a small rate of seed germination. Thus a certain fraction of non-germinated seeds persists in the soil, which will germinate later or even only in the following year. Without stimulation of seed germination the stand will appear jaggy. This could be avoided with a higher sowing density (but then singling might be necessary later). Germination rate is improved by frost events. It is recommended, therefore, to store the seeds in a refrigerator at 3-6 oC for some weeks before sowing. Storage at -20 oC (not soaked but dry!) for one week is also recommended for stimulation of seed germination. The seeds must not be moistened before sowing, because then the mechanical single grain dispersal will not work.