Abstract
The effect of placing sediments, deposited over a one-year period in a fish pond, onto intercropped maize and mungbean and monocropped maize was investigated. Two cultivation techniques were used: the first to hoe in the sediment before rice straw was placed on top of the soil; the second to place the sediments on top of the rice mulch. For both systems, planted in late 1982 and early 1983, three dosages were tested, equivalent to 19.5, 39 and 78 kg m-2 of sediment. Yields of maize showed no significant change when the sediment was hoed into the soil, but decreased steadily with increasing sediment doses when these were placed on top of the rice straw. A similar decrease, although less marked, was observed for mungbean. Soil analyses indicated that sediments from ponds stocked with bottom-feeding fish, e.g. common carp, may be poorer than those from ponds stocked with column feeders. Similarly, sediments may be more nutrient-rich where large amounts of organic matter continuously enter the pond. In such cases, where sediments are valuable, it would still be advisable to remove organic matter before placing the sediments onto the fields in order to avoid the negative effects reported here.
