Composting Rice Straw in Semi-Arid Conditions

Five experiments were conducted, three with 10-kg lots (in cement cylinders/digesters) and two in heaps with 500-kg lots of rice straw. Results from three—one with cement cylinders and two with heaps—are reported here. All were conducted at Patancheru from 1998 to 2000 in the hot summer period (April–May). The use of 0.76% N (as urea) with or without added micro-organisms more quickly decomposed the rice straw (by a subjective visual rating scale and C:N ratio) by about 1 week than otherwise. Also, the compost of N-applied treatments had at least 40% more N than that from the non-applied control. But N loss, indicated by the odour of ammonia, was noticed only from the N-applied treatments. All the treatments, except the control, received 25% rock phosphate (RP), when composting was done in cement digesters. For heap composting, RP was reduced to 6% so that its concentration would not be excessive when the compost is applied to crops at high rates. Composting was accomplished within 45 days whether in the digesters or in heaps, even with a reduced use of N (0.36% in 1999 and 0.1% in the year 2000). Treatment effects due to N that were apparent in the final product, disappeared when N-application was reduced to 0.3% or 0.1%. It was only through the visual rating that amendment with N and micro-organisms was perceived to shorting composting time. The resultant compost, however, did not indicate differences in chemical characteristics (N, P, K, OC%) across treatments in heap composting. One apparent biological difference across treatments was the presence of fruiting bodies of Sclerotium rolfsii (causes root rots in many crops) in control treatments. This fungus was not seen in treatments receiving microbial inoculation. In the experiment in 1999, we composted over 6 t of rice straw in a single session, in multiple heaps of 500 kg. The composting protocol is proposed for a small-scale village-level enterprise and is not intended for individual farmer