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Sesbania sesban was evaluated as green manure crop for lowland rice in the Dry Zone of Sri Lanka. The legume was grown during a fallow period before lowland rice (Oryza sativa) and ploughed under just before transplanting. Weight loss and nitrogen content in litterbags containing leaves, stems and roots of the legume were monitored. Comparisons were made between rice yields from 20m 2 plots after green manuring in combination with different nitrogen fertilizer levels (0, 2.4, 4.8 and 7.2gm z) and nitrogen fertilizer (9.6 g m 2) alone. Above-ground biomass of S. sesban was 440 g m 2 (dry wt) when ploughed under after 84 days growth. N-content in leaves, stems and roots was 3.760,0.41% and 0.73%, respectively. This gave a N-input from S. sesban of 9.2 g m 2 (8.3 g from above-ground parts and 0.9 g from roots). The corresponding K and P inputs were 7.3 and 0.6gm 2 respectively. The nitrogen rich leaves, which contained 88% of the nitrogen in the above-ground parts, decomposed and released its nitrogen much more rapidly than the stems and roots. After only four days the leaves had released 5.3 g N m -2 and after 14 days they had released 6.4 g N m 2. The highest rice yield (505 g m 2) was obtained using S. sesban and 4.8 g m 2 of N-fertilizer. The yields with only N-fertilizer or only S. sesban were 442 g m -2 and 396 g m -2, respectively. Due to the rapid decomposition of the nitrogen rich leaves, S. sesban did not behave as a slow release fertilizer. Thus, it is not necessary to apply nitrogen fertilizers as a basal dose.

Management and environmental constraints to rice yield in a paddy tract (lowland rice field) was studied within a village irrigation system in Sri Lanka. The relative importance of water coverage during the critical period and soil fertility variables on the yield variations were analysed. For the upper part of the paddy tract having adequate water supply, environmental and management factors seemed to explain the large variations in yield. For the middle and lower parts, with a shortage of water, water coverage was the only significant explanatory factor.For efficient use of a scarce water supply farmers allocated water first to the upper part, which resulted in water deficiency further down. An alternative strategy for water allocation, where the lower more fertile part of the paddy tract is favoured, would not avoid the risk of water scarcity for the individual farmer but there would be a potential for increase in the total production.

No abstract

In the municipality of Sund, located in a sensitive rural area in Åland, a demonstration project is now carried out with the overall objective to move the most concentrated fractions of wastewater from the coastal area to a treatment plant situated close to arable land. Blackwater and greywater septic sludge from about twenty households and two tourist camps are treated together with energy rich organic material from a nearby potato-chip factory. The collection concept is based on the use of extremely efficient water-saving toilets, with separate systems for the blackwater and greywater in the households. The collected materials are co-treated in a batchwise aerobic thermophilic treatment process (wet composting process), where the materials reach at least 55°C during a minimum of 10 hours. The dry matter content of the collected material was about 2%. After stabilisation and sanitation (by the temperature rise caused by microbial activity during the treatment process), the compost slurry is utilized as a liquid organic fertilizer on arable land.