Soil strain transducers were used to determine strain in an initially loose sandy loam soil in a soil bin beneath the centerline of an 18.4R38 radial-ply tractor drive tire operating at 10% travel reduction. The initial depth of the midpoints of the strain transducers beneath the undisturbed soil surface was 220 mm. Strain was determined in the vertical, longitudinal, and lateral directions. Initial lengths of strain transducers were approximately 118 mm for the longitudinal and lateral transducers and 136 mm for the vertical transducer. The tire dynamic load was 25 kN and the inflation pressure was 110 kPa, which was a recommended pressure corresponding to the load. In each of four replications, as the tire approached and passed over the strain transducers, the soil first compressed in the longitudinal direction, then elongated, and then compressed again. The soil was compressed in the vertical direction and elongated in the lateral direction. Mean natural strains of the soil following the tire pass were −0.200 in the vertical direction, +0.127 in the lateral direction, and −0.027 in the longitudinal direction. The mean final volumetric natural strain from the strain transducer data was −0.099, which was only 35% of the mean change in natural volumetric strain calculated from soil core samples, −0.286. This difference likely resulted from the greater length of the lateral strain transducer relative to the 69 mm lateral dimension of the soil cores. The strain transducer data indicated the occurrence of plastic flow in the soil during one of the four replications. These results indicate the complex nature of soil movement beneath a tire during traffic and emphasize a shortcoming of soil bulk density data because soil deformation can occur during plastic flow while soil bulk density remains constant.

Conservation farming systems are rapidly increasing in popularity. As these changestake place, there is an obvious need to maximize the efficiency and effectiveness of the morecommon conservation farming tools. Chisel-sweep systems have an advantage over manyconservation tillage tools because they maximize the residue left on the surface for erosioncontrol while providing the tillage necessary for weed control and seedbed preparation. Theaccumulation of residue within the confines of the tillage tool is a common problem. The properclearance vertically between the soil surface and the supporting framework for the tillage deviceis necessary for the passage of residue. A coulter directly ahead of the wingtips of each leadingsweep, operating at the same depth as the sweep, reduced draft of the sweep-coulter systemup to 45% as compared to the draft of a sweep plus coulter system with the coulter operatingdirectly ahead of the sweep center. Coulters directly ahead of the wingtips of sweeps permitpassage of the sweeps through heavy residue without problems of residue clogging, althoughthere is a tendency for more residue buildup on the sweep shanks when wingtip coulters areused.

A method to quantify the spatial stress distribution will be introduced and first results will be discussed. This method allows the detailed analysis of principal and shear stresses as well as the determination of the direction angle of principal stresses and the octahedral shear stress angle.The described Stress State Transducer (SST) is composed of six single strain gage sensors that enable the accurate and recording of stresses in six directions in a wide load range. Their data form the base for calculation of spatial stress distribution.Some first results show that in a luvisol derived from loess wheeling at a wheel load of 4.0 Mg induces high shear stresses in a depth of 30 cm. This probably causes plastic soil deformation.

Prescribed tillage to meet aronomic needs will be important to future goals of productivity, energy efficiency, and resource conservation. Control systems will be an important feature of the tillage systems that are developed to implement prescribed tillage. A control concept for tillage systems is described. 6 refs.

ABSTRACT A three-point hitch accessory was designed and constructed to measure draft, vertical force, and torque simultaneously and independently in a vertical longitudinal plane caused by an implement. Special features of the force dynamometer are dual-loading range and fast-hitching capability. The force dynamometer is designed for tractors in the 75- to 100 kW power range with maximum draft capacity of 66,700 N in the dynamometer's high-range and 36,000 N in the low-range.