Long-term effects of composted cattle manure on biomass production, nutritive value, and digestibility of dwarf late Napier grass

Composted cattle manure provides essential nutrients and organic matter that improve soil fertility and support forage production on marginal lands. Dwarf late (DL) Napier grass [ Cenchrus purpureus (Schumach) Morrone (syn. Pennisetum purpureum Schumach)] is a high-yielding tropical forage whose productivity and nutritive value depend heavily on appropriate nutrient management. This study evaluated the long-term effects of composted cattle manure application on the biomass production, nutritive value, fiber composition, and digestibility of DL Napier grass over two consecutive years under a tropical cut-and-carry system. A field experiment was conducted on marginal soils using a randomized complete block design with three replications. Four manure application rates were evaluated: 0.00, 1.38, 2.88, and 4.67 g nitrogen (N) m −2 per application. Over both experimental years, manure application linearly enhanced dry matter yield (DMY) and crude protein (CP), while decreasing structural fiber fractions. Annual DMY in the first year increased significantly (p<0.05) from 339.1 g m -2 in the control to 3375.5 g m -2 under the highest manure rate. Concurrently, mean CP content increased dose-dependently from 9.32 g 100 g −1 to 14.65 g 100 g −1 in Year 1, whereas neutral detergent fiber (NDF) and acid detergent lignin (ADL) decreased. Forage quality improved with increasing manure application; notably, stem in vitro dry matter digestibility (IVDMD) in the second year rose from 71.87 g 100 g −1 (control) to 77.93 g 100 g −1 at the highest dose during Cutting III. It is concluded that applying composted cattle manure at the highest rate of 4.67 g N -2 per application performed best, providing a sustainable strategy to maximize biomass yield and structural tissue quality under marginal tropical conditions.