I worked with litter decomposition in Sandbanks and in forests. What do you need? I have this publication "Matter turnover in the oligotrophic restinga ecosystem and the importance of the key species Clusia hilariana". If do you have more questions, please send me message.
You could look at the manuals of forest monitoring schemes that include decomposition. ICP Integrated Monitoring for example has a description of the method under Optional subprogramme MB: Microbial decomposition. The manual is available here: