Leonard L. Bashford

NORMALIZING CONE RESISTANCE VALUES BY CovARiANCE ANALYSIS

Measured cone index values were adjusted for soil water content and bulk density by normalizing their effects using a covariance analysis as described by Christensen et al. (1989). Cone indices adjusted by covariance analysis allowed the testing of tillage differences at a given depth and across depths. The procedure showed that double disking a Sharpsburg silty clay loam soil reduced the cone penetration resistance to 152 mm depth. The penetration resistance was similar in the deeper undisturbed zones. Unadjusted field measured cone indices showed differences in the deeper zones though no tillage was performed.

TRACTIVE PERFORMANCE COMPARISONS BETWEEN A RUBBER BELT TRACK AND A FOUR-WHEEL-DRIVE TRACTOR

ABSTRACT Field tests were conducted to evaluate and compare the tractive performance of a rubber belt track tractor and a four-wheel drive tractor. Data were obtained by drawbar tests on each tractor operating on four ground surface conditions: untilled oats stubble, disked oats stubble, plowed oats stubble, and com stubble. Tractive performance comparisons between the two test tractors were made by comparing the relationships of dynamic traction ratio and tractive efficiency to slip. In general, the rubber belt track tractor exhibited small tractive performance advantages over the four-wheel drive tractor on firm surfaces with more significant advantages on soft surface conditions.

Improvement of Tractor Performance

Improvement of agricultural tractor performance was analyzed using the data from 926 diesel tractors tested at the Nebraska Tractor Test Laboratory from 1959 through 2002. The performance analysis included the specific volumetric fuel consumption, power per unit weight, traction coefficient, maximum torque rise, and sound level. They were evaluated based on the PTO power level and chassis type of tractor. Some of the results are: (1) The average specific volumetric fuel consumptions for the maximum PTO and drawbar powers increased by 20.5% and 23.4% to 3.47 kW·h/L and 3.01 kW·h/L, respectively, from 1959 through 2002. (2) The average maximum PTO and drawbar powers per unit weight of ballasted tractors increased 72.1% and 66.2% to 1.48 and 1.28 kW/kN from 1959 through 2002. (3) The traction coefficient increased 24.4% for 4WD tractors and 27.4% for standard tractors from 1959 through 2002, resulting in 1.02 and 0.94 for 2001-2002 respectively. In the 2001-2002 period, the average torque rise of the tractors in a PTO power range of 37-75 kW was 27.7%, which was 18.4% increase from 1992 through 2002. The tractors with greater PTO power than 187 kW had an average torque rise of 50.8%, which was 30.9% increase over the same period. The maximum sound level within the cab in the early 1970’s ranged from 83.0 to 93.6 dBA and reduced to 73.5 to 88.5 dBA in the 2001-2002 period, which was about 9.3% to 21.5% reduction from 1972 through 2002.

DESIGN AND EVALUATION OF A PUNCH PLANTER FOR NO-TILL SYSTEMS

A punch planter for corn was designed, prototyped, and evaluated for no-till conditions using a commercial seed metering unit. The seed meter was evaluated for seed spacing performance at the vertical position with 2.5 kPa of vacuum, as specified by the manufacturer, and at a 22° incline with 4.0 kPa of vacuum. The prototype punch planter was evaluated at a 22° incline with 4.0 kPa of vacuum. Only small changes occurred in the seed meter performance when speed varied from 1 to 3 m/s. The precision of seed spacing decreased approximately 6.0% when compared with the seed meter results. Field tests were conducted with several residue covers for testing the residue effect at a speed of 2.0 m/s. No significant difference was observed in the planter performance. The multiples index (more than one seed in one space) increased up to 5.0% when compared to laboratory results. Emergence may have been affected by environmental conditions, but the precision during field tests was better than in the laboratory tests.

Comparison of Bulk Density Beneath a Belt Track and Tire

WHEEL traffic is considered a major cause of soil compaction in production agriculture. Soil compaction depends on initial conditions, load, contact area and tire type and shape at the soil surface. The use of tractors equipped with tracks instead of tires has the potential of reducing soil compaction because of reduced surface contact pressure and difference in load distribution over a relatively long-narrow track. The introduction of a new agricultural tractor equipped with a rubber belt track permits a crawler tractor to compete with a large four-wheel drive tractor in both speed and mobility. Soil bulk density was measured as an indication of compaction which results from trafficking with a rubber belt track tractor and a four-wheel drive tractor. The measurements were taken on three tillage treatments at three soil water contents. Most of the comparative differences in bulk density resulting from trafficking with the two tractors were non-significant at the 0.10 level. Bulk densities at the deeper depths were significantly higher for the tire than the rubber belt track for some tillage treatments. However, in all comparisons, bulk density resulting from the rubber belt track was numerically less than from the tire.

Tractive Performance of 18.4R46 and 18.4R42 Radial Tractor Tires

Tractive performance of 18.4R42 and 18.4R46 tractor tires mounted on two-wheel drive (2WD) and mechanical front-wheel drive (MFWD) agricultural tractors was evaluated on three different soil surfaces. Field data were collected and predictive equations were developed for gross traction ratio, dynamic traction ratio, and tractive efficiency for the 2WD. Predictive equations for the dynamic traction ratio were developed for the MFWD. Due to firm soil conditions and excessive inflation pressures, no apparent traction gain from the 18.4R46 tire was obvious.

Peristaltic Pump Accuracy in Metering Herbicides

Two peristaltic pumps metered three undiluted liquid herbicide formulations at two formulation temperatures, 5° C (41° F) and 43° C (109° F), and two pump outlet pressures, 7 kPa (1 psi) and 69 kPa (10 psi). The maximum error in the volumetric metering rate was 41% for the smaller pump and 111% for the larger pump. Herbicide formulation and temperature significantly affected the mass and volume of herbicide metered per pump revolution, but pressure had no significant effect. The pumps tested need to be calibrated for the particular formulation and temperature used, to avoid exceeding the recommended allowable error for chemical application.

Performance Comparisons Between Duals and Singles on the Rear Axle of a Front Wheel Assist Tractor

ABSTRACT DYNAMIC traction ratio and tractive efficiency of a tractor, equipped with dual or single tires on the rear drive axle, and a mechanical front-wheel drive assist, were evaluated on four different surfaces; con-crete, disked sandy soil, disked wheat stubble and plow-ed wheat stubble. When operating on concrete, a higher dynamic traction ratio was found for the duals than singles. However, when the tractor was operated in the field on the different soil surfaces, no discernible perfor-mance difference in the dynamic traction ratio or tractive efficiency could be detected between single or dual tires on the rear drive axle.

Bi-level Subsoiler Performance Using Tandem Shanks

A subsoiler was modified by mounting a shallow shank ahead of a conventional subsoil shank. Wings with a total effective width of 300 mm (12 in.) were attached to the foot of the shallow shank. The surface soil was lifted by the winged foot of the leading shallow shank before the soil below the shallow shank was fractured and lifted by the deeper shank. Power requirements and soil eruption were used to evaluate the effect of treatments of the bi-level subsoiler. Treatments consisted of the following shank combinations: 1) conventional shank at 457-m (18-in.) depth with variable shallow winged shank depths and 2) shallow winged shanks set at 229 mm (9 in.) above the conventional shank and deep shank depths of 356, 406, and 457 mm (14, 16, and 18 in.). Tandem shanks have the potential for increasing tillage efficiency.

Wide Tires, Narrow Tires

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.