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Tractive performance comparisons among five different size tires were made on two different surface conditions, a wheat stubble field and a tilled wheat stubble field. Radial 18.4R46, 20.8R42 and 710/70R38 radial tires; and bias 750/65-38 and 850/55-42 tires were used. Instrumentation to evaluate tractive performance was installed on a two-wheel drive and a mechanical front wheel drive agricultural tractor. Axle torques, drawbar pull, travel speed, and engine rpm were recorded for a series of drawbar pulls on the two soil surfaces. Tractive performance evaluations among the tires were made by comparing the relationships of dynamic traction ratio to slip, tractive efficiency to slip, and tractive efficiency to dynamic traction ratio. In general, narrower tires exhibited performance advantages over wider tires.

Data obtained when harvesting with a combine equipped with a yield monitor were used to develop yield maps. A prototype yield monitor was developed that uses a combination of light emitters and receivers mounted in a rectangular frame. The monitor was mounted in the combine in the top of the clean grain elevator. As grain flows through the monitor, a voltage change proportional to light reduction was recorded. This voltage was then correlated to grain flow rate. At the same time, site-specific location was recorded using the global positioning satellites (GPS) system. The location data, yield monitor output, cutting width, and combine forward speed were stored in a spreadsheet format. The data were then used to prepare the yield maps.

Two peristaltic pumps were tested to determine their accuracies in metering three liquid herbicides for injection-type sprayers. To maintain acceptable chemical application accuracy from either pump, recalibration is necessary if the formulation or its temperature changes. An experimental thermal flowmeter was developed and evaluated along with turbine and piston flowmeters. The piston flowmeter had the best linearity and smallest time constant. A system to control the flow rate of the injected chemical is proposed and was simulated to determine its dynamic response. The proposed chemical metering system, coupled with plumbing systems of sprayers used by private and commercial applicators, were simulated to predict chemical application accuracies.

In order to evaluate tractor performance, axle torque and speed are required to calculate axle power. The ability to develop torque in drive axles of agricultural tractors is dependent on dynamic axle load, the tire-surface interface and surface conditions. The factor limiting tractive performance could be any one of the forementioned variables. In large four-wheel drive tractors, equal torques in the front and rear drive axles are desirable under normal tractor operations to insure favorable drive train life. Presented in this paper is a summary of axle torques observed during operation of front-wheel assist and four-wheel drive agricultural tractors during performance evaluations on several different soil surface conditions.

The distribution of ballast did not affect tractive performance of a tractor equipped with a mechanical front-wheel drive assist in tests conducted at the University of Nebraska-Lincoln. However, the torques developed in the front and rear drive trains were directly related to ballast distribution and the dynamic load on the drive wheels.