SUMMARY
In tidal swamp land, fast growing and very fertile weeds can produce biomass of around 3.0-3.5 t ha-1 of dry matter on acid sulfate lands and 1.66-2.04 t ha-1 on peatlands (Simatupang et al. al., 2001). The weed biomass can be utilized and returned to the soil both in-situ and ex-situ which will be useful for increasing soil organic matter and increasing soil fertility. The results of the analysis of composted weed biomass can contribute significant nutrients N, P and K to plants if the compost is add to the soil. This research used water swamp weed Eichhornia crassipes (hyacinth), Pistia startiotes (apu wood), and Eleocharis dulcis (purun rat as raw materials for making compost which was added with manure and EM-4 as a decomposer. The composting process was carried out for 21 days with the observed parameters including color, odor, temperature, pH, levels of nutrients N, P, K, Ca, Mg and levels of C-Organic and C/N materials. The results of the analysis of the chemical quality of weed compost for the temperature during composting ranged from 35oC, while the chemical content such as pH, C-organic, N, P, K Total, Ca, Mg, and Fe met the standards of SNI 19-7030-2004. Meanwhile, the C/N of purun rat compost did not meet the SNI standard, which was 23.