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]
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