Investigating the importance of solid piggery sludge application in soil for signal grass (Urochloa decumbens) production in the humid lowland agroclimatic conditions in Papua New Guinea

The ruminant livestock industry in Papua New Guinea is yet to be fully developed because grazing is entirely on unimproved, native, and hardy pastures that are poor in nutrients and hardly palatable. A field trial was conducted with four rates of amendments (0, 2.5, 5.0, and 10 t.ha-1) as treatments by growing signal grass to investigate the potential use of solid piggery sludge to improve its productivity. The treatments were replicated five times (n = 5) and set up in a completely randomized block design. The plants were harvested after six months, and soil samples collected were used to assess the changes in soil chemistry. The amendments improved all the soil parameters, nutrients, overall productivity, and yield. At 5–10 t.ha-1, soil organic matter, soil organic carbon, cation exchange capacity, and electrical conductivity, for example, improved by 169–254%, 534–643%, 37–91%, and 10–27%. Similarly, N, P, K, and S were increased by 41–52%, 144–267%, 188–325%, and 750–1,250%. Among the potentially toxic metals, Cu, Pb, Cd, and Cr were higher than standard permissible limits. Overall, the highest dry matter yield (37-58%) was produced by 5.0 and 10.0 t.ha-1 rates, respectively. Although accumulation in soil and biomass of metals was evident, the soil parameter data did not support possible mobility. Therefore, 5.0 t.ha-1 was found to be crucial for signal grass production.