A bush chopper for mulch production in fallow-based agriculture and
resource conservation
Manfred Denich', Andreas Block2, Wolfgang Lücke2 and Paul L.G. Vlekl
'Institute of Agriculture in the Tropics, 2Institute for Agricultural Engineering
University of Gõttingen, Germany
Shifting cultivation is still the most important small farmer land-use system in the Northeast
of Pará state, Brazil. Traditionally, this system consists of a 2-year cropping period followed
by a fallow period of several years. Land preparation prior to the cropping is done by burning
the slashed fallow vegetation. Intensification of land-use, but keeping the traditional
agricultural practices leads to a decrease of the systems productivity. A key factor of that
degradation are the nutrient losses due to slash burning. These losses are one of the main
causes for the negative nutrient balances (inputs of nutrients are lower than outputs) of the
land-use cycle, e.g. for a 2-year cropping and a 7-year fallow period without fertilization the
balances are: N -180 kg ha-I, P -7, S -12, K -86, Ca -126 and Mg -12). Furthermore, during the
burn 13,000 kg ha-I of carbon or 98% of the above-ground C stocks are released to the
atmosphere, the respective biomass of which could contribute substantially to the management
of the soil organic matter to improve the physical, chemical and biological soil properties.
Therefore, cropping experiments with fire-free land preparation have been carried out by
chopping the biomass of the fallow vegetation and spreading it as mulch over the field. For
the adoption of that technology by the farmers practical methods for the conversion of woody
bush fallow in mulch material are of fundamental importance and the application of
machinery is absolutely necessary. The following demands were made on the implement: (1)
cutting the woody vegetation near the ground (to make weeding easier) without destroying the
root system of the vegetation (to assure the regrowth of a woody fallow vegetation), (2)
chopping the plant material, (3) spreading the chips homogeneously over the field. The
construction of the chopper should be simple and robust. Accordingly, the Institute for
Agricultural Engineering of the University of Gõttingen developed a tractor-propelled bush
chopper, which is mounted on the front power lift. Driving forward (1-3 km h-I) the
vegetation is cut in a width of 2m by two rotating circular saws (diameter 1m) and
subsequently chopped by two vertical steel helíces sitting on the saw-blades. Paddles between
the saw-blades and the hei ices throw out the chopped material towards the back and under the
tractors front wheels. The power demand for chopping a 3 to 4-year-old fallow vegetation is
at least 60 kW. The average rate of output is 10 t (8-17 t) chopped fresh plant material per //
hauro Accordingly, one hectare of 3 to 4-year-old fallow vegetatíon can be chopped within 4-5/'-hours (for further information see the abstract by Block, Lücke, Denich, Vlek). The feasibility
of the new technology will be shown, problems pointed out and modificatíons of the prototype
suggested.
Mailing address: IGrisebachstr. 6, 37077 Gõttingen; 2Gutenbergstr. 33, 37075 Gõttingen,
Germany; e-mail: [email protected]