International Soil Tillage Research Organization

RESULTS AND DISCUSSIONDRAWN SWILER Fig.5 shows a displacement and stress field analyzed byFEM for a subsoiler nevmnt with injected sewage sludge. If the slip lineinduced by mvemnt of the subsoiler standard is not hve the slip lineinduced by the injected sewage sludge, a larger draft reduction can be expectedbecause a larger volm of soil is broken down. Consequently thenozzle port should 22 separate from the subsoiler standard, i.e. the chiselshould be as long as strength pennits, and the nozzle port should be at thetip of the chisel.Fig.6 shows a Wle oscilloqram from an experimental test run. In thiscase, when sewage sludge was injected continuouslyat a rate of 320 g/s and the operatingspeed was 26 Ws, a pressure of 80 kPawas produced at the nozzle port. A basedraft of 750 daN was measured when no sludgewas injected. Draft was reduced to 450 daNby injection of sludge containing 93 % misture.The pressure produced at the nozzleport is h u t 0.1 MPa, which was not extrenelyhigh. The draft reduction was affectedby the operating speed, the flow rate of injectedsludge and the base draft as neasuredwhen no sludge was injected. Fig.7 showsthis relation for 26 4 s operatmg speed.When the flow rate of injected sludge waslow, such as 160 g/s, and the operatingspeed was extremly slow, such as 1.6 ads,the sludge had little disruptive effect onthe soil with mst of the sludge flowingout to the subsoiler path along the surfaceof subsoiler. In cases when a lubricatinseffect on the subsoiler by sludge occurred, Fig.4 Rotary subsoiler withlittle draft reduction was observed.pressurized sewageSchafer et al. (1975, 1977, 1979) reportedsludge injection usedthat the draft of plows could he reduced by in soil bin study.lubricatins the surface of plows.~ usince t in the case of the subsoiler,the surface area in wntact with thesoil is comparatively m11, thelubricating effect for the draft reductionis not significant. A stabledraft reduction could he observedwhen the operating speeds increasedfrom 6 to 26 my's. The mink flowrate of injected sludge required fora reduction of draft was approximately6 g/s for each centhter of mvementof the subsoiler. Fig.8 shows acrosssection of the subsoiler path. A V-shaped breakdain of the soil layercontaining the sludge was observed.There was also a great deal of sludgeon the chisel path at the center of V.A benefit of sludge injection in reducingthe total pmer required iswFig.5 Displacement and stress fieldafter 5 can subsoiler mvemetinjecting sewage sludge of320 g/s in soil having 15%misture.