Study was conducted on the role of nitrogen (N), applied either alone or in combination with phosphorus (P), in composting of kallar grass [Leptochloa fusca (L.) Kunth] with particular emphasis on carbon (C) and N conservation during composting. Nitrogen was added as ammonium sulphate and P as single superphosphate. Addition of N alone, though accelerated the composing rate, it did not conserve C and N during composting. However, application of P along with optimum level of N accelerated the composting rate, stimulated the substrate transformation into humic acid, and decreased the N loss. The results emphasized the need of phosphorus amendment along with nitrogen to conserve C and N during composting of kallar grass.