Draught requirement of trailing-foot and shallow injection equipment for applying slurry to grassland

Surface spreading of slurry leads to the inevitable emission of ammonia into the environment. Injection of slurry on grassland reduces these emissions. However, injection of slurry by deep working injector tines with goose foot chisels (wings) requires high draught forces. This type of injection has the risk of the crop dying back under dry soil conditions and is not possible on all soil types. In recent years, new slurry application techniques for grassland have been developed that achieve a large reduction in emissions of ammonia, but require less draught force. These techniques include cutting a shallow slit in the sward, into which slurry is applied, and application of the slurry in bands on the soil surface using a trailing foot implement. In a series of experiments on sandy loam, day and peat soils, the draught force requirement of single elements of five new slurry application techniques was investigated. The application techniques were a trailed sliding foot element and four shallow injection elements: angled-disc coulters (double-disc opener), thick-disc coulter, flat disc coulter followed by a vertical injection coulter and knife coulter followed by a vertical injection coulter. The application technique, working depth and soil conditions had a significant influence on the draught force. For a working depth of 5 cm, the required draught forces per shallow injector element, measured in this experiment, were in the range of 202-706 N for a double-disc opener, 284-991 N for a thick-disc coulter, 361-1260 N for a flat-disc coulter plus injector and 389-1358 N for a knife coulter plus injector. The lowest draught forces occurred on peat soil and the highest forces on dry clay. The trailing foot required an average draught force of 39 N. The draught force of the trailing foot did not relate to the soil conditions but an effect of the grass sward condition was suggested. (C) 1998 Silsoe Research Institute.