Effect of Digested Effluent of Manure on Soil Nutrient Content and Production of Dwarf Napier Grass in Southern Kyushu, Japan

The objective of this study was to determine the nutrient content of soils and digested effluent of manure (DEM) and to investigate the production of dwarf Napier grass under repeated defoliation employing three treatments comprising three rates of DEM application and a control using chemical fertilizer. The most abundant cations in the DEM solution were ammonium, followed by potassium, sodium and calcium, with the calcium concentration approximately one-fifth that of ammonium. The pH of the soil solution ranged between 6.6-8.0 and tended to increase with increasing DEM application rate which in turn generally reflected the change in electric conductivity of the soil solution. The most abundant cations in the soil solution were calcium which accounted for 62% of cations across all treatments and seasons, followed by magnesium and sodium. Crop growth rate was positively and linearly correlated with leaf area index, suggesting that the increase in plant production due to application of DEM or chemical fertilizer is similarly mediated by leaf area development.