Search

Abstract: Production of biogas from energy crops of agricultural origin is regarded as a promising alternative to decrease dependence on non-renewable energy sources. A model was built to evaluate the handling system comprising harvest, transport and ensiling of forage intended for production of CH4-enriched biogas for vehicle fuel. The model was applied to a full-scale plant in Sweden producing biogas from organic household waste and forage. Timeliness, capacity and harvesting costs were studied by varying transport system design, transport distance, field size and dry matter (DM) yield. Matching harvest and transport capacity is essential in minimising the time required for harvesting and the resultant costs. However, this study showed that keeping the harvest and transport capacity sufficiently high to avoid idle time did not necessarily result in the lowest costs. By adapting the transport system, it was possible to reduce costs by 30% when the average transport distance was decreased from 17 to 8.5km. The study showed that with forage for biogas production, it was optimal to harvest later than the normal dates for harvesting forage for milk production, since the lower biogas production per kg DM was compensated for by higher DM yield. As long as the harvest started on the days calculated as being optimal with respect to the value of the harvest, timeliness costs made up less than 4% of total costs depending on the transport system chosen. When the start of harvest deviated from the optimal, timeliness costs increased substantially. Delayed harvest had even larger impact on the total harvest costs. [Copyright &y& Elsevier]

Abstract: Water hyacinths are becoming a problem in lakes, ponds and waterways in many parts of the world. This paper contains a literature study of different ways to use water hyacinths, mainly in agricultural or alternative energy systems. The literature review indicated that water hyacinths can be rich in nitrogen, up to 3.2% of DM and have a C/N ratio around 15. The water hyacinth can be used as a substrate for compost or biogas production. The sludge from the biogas process contains almost all of the nutrients of the substrate and can be used as a fertiliser. The use of water hyacinth compost on different crops has resulted in improved yields. The high protein content makes the water hyacinth possible to use as fodder for cows, goats, sheep and chickens. Water hyacinth, due to its abundant growth and high concentrations of nutrients, has a great potential as fertiliser for the nutrient deficient soils of Africa and as feed for livestock. Applying the water hyacinths directly without any other processing than sun drying, seems to be the best alternative in small-scale use due to the relatively small losses of nutrients and workload required. To meet the ever-growing energy demand, biogas production could be one option but it requires investments and technological skills that would impose great problems in developing countries where the water hyacinth is often found. Composting as an alternative treatment has the advantage of a product that is easy to work into the soil compared with dried water hyacinths, because of the decomposed structure. Harvesting and transport of water hyacinths can be conducted manually on a small scale and does not require a new harvesting technique to be introduced. Transporting of fresh water hyacinths means, if used as fertiliser in amounts large enough to enhance or effect crop growth, an unreasonably large labour requirement. Based on the labour need and the limited access to technology, using dried water hyacinths, as green manure is a feasible alternative in many developing countries. [Copyright &y& Elsevier]

Optimal crop and machinery systems are essential if organic farming is to be economically competitive. The aim of this study was to examine how the capacity of an optimal field machinery system is affected with respect to economy when a farm converts to organic production. An important part of the work was to calculate timeliness factors valid for organic farming. A case study was made for a typical arable farm in the south-central part of Sweden. To keep the scope manageable, the focus was on two of the most important machines used; the seed drill and the combine harvester. Machinery costs consist of three parts: direct machine costs, labour costs and timeliness costs. For optimisation of farm machinery systems, a method based on linear programming was used. The optimal size of the seed drill and combine harvester increased when the arable farm in this study converted to organic production. The total machine costs were 7% higher in conventional production but calculated per kg grain produced the machine costs were 58% higher in organic production. The main differences in timeliness costs between organic and conventional farming can be attributed to two counteracting facts: the lower yields and the higher product prices in organic farming. Timeliness cost per kg cereal produced was higher in organic production. [Copyright &y& Elsevier]