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Automatic guidance of farm tractors would improve productivity of many field operations by reducing operator fatigue and by improving machine performance. A self-tuning steering controller, which can be used for noncontact positioning systems, was designed for tractor guidance. A simple two degrees-of-freedom model was chosen with which to develop a prediction model used in recursive least-squares parameter estimation. A variable forgetting factor was implemented and its algorithm modified to cope with time-varying nonlinear systems. The self-tuning steering controller based upon minimum variance control was tested and verified with a tractor dynamic simulator. Circular, lane change, and sinusoidal paths were used. A model tractor was also used to verify controller performance for staight-line and sinusoidal paths.

This paper reviews literature on yield response of crops to soil compaction. Because soil compaction interacts with several other factors it is difficult to clearly define its effect on yield. In general, increasing soil bulk density is detrimental to crop growth. However, some compaction frequently improves crop production. Usually this occurs in dry conditions and often results from better stand establishment or nutrient uptake. In many situations compaction has little effect on crop yield. This is likely when factors other than those affected by soil density are limiting crop growth.