New behemoth machinery is cutting wide, efficient swaths across US farms

Paul Bunyan, that super-performer of lumberjack tasks in the mythical forests of the West, would like what American farmers are doing. They are learning - with new Bunyanesque technology - to plant, grow, and harvest crops more efficiently, using almost bigger-than-life tractors, planters, sprayers, and harvesters.

Tractors of double and triple the horsepower of a few years ago are becoming common equipment on the farms. Larger models of 500 to 600 horsepower pulling heavy, complex rigs have proved highly efficient, since they use half as much fuel as several smaller units on a given acreage.

Oversize tractors have been found most suitable for wheat, corn, and soybean growers, for whom big equipment for planting and tillage means fewer runs across the land. Multirow planters, six times the size of those of 10 years ago, are in wide usage, according to the United States Department of Agriculture's (USDA) Economic Research Service studies. New 20-foot-wide drills have been developed which carry 25,000-pound payloads. And these have the ability to cut fuel usage from 61/2 gallons per acre to 11/2 gallons by the reduction of tractor trip runs.

Planter-cultivator systems are gaining favor, because they control soil erosion and conserve moisture better for growers than conventional methods that turn the soil.

Sprayer techniques are also changing. Some larger planter and field preparation machines apply chemicals simultaneously with other, normal farming processes. ''Knifing-in'' - cutting slit trenches to apply chemicals below the surface - is said to eliminate a good deal of waste which can occur with the surface broadcasting of chemicals.

Irrigation systems that require pumping and often gravity assistance are contributing to new US farm efficiency. New lateral-move units can cross a field using a single pump. Former methods required several pumps and thus more expensive energy backup. Some irrigation units are being controlled by computers and equipped with lasers for uniform alignment of the field, as well as with soil and water sensors to judge the need for added moisture.

Harvesting machines being manufactured are getting almost big enough for Bunyan himself. Some new combines can harvest 2,000 bushels an hour - five times the capacity of machines of 10 years ago.

Wheat farmers may soon be able to buy combines with 40-foot grain heads. A 40 -foot swather to cut and windrow hay is in the late design stage. A new 4-row cotton harvester has been introduced in the Southwest fields. It reduces harvesting costs (labor and fuel) by about 16 percent; and with new techniques, dumps the picked, raw cotton in compressed stacks for field pickup.

These innovations mean greater farm efficiency through higher productivity and fewer machines required.

Another newly applied hi-tech usage on certain US farms is the laser-leveling process. It works this way: fields using irrigation are first graded by conventional earth-moving equipment. Then a laser beam set at a specific grade level is transmitted by a rotating command post to receivers that activate tractor-mounted scrapers. This way, the land gets almost absolute uniform grading.

Land leveling is particularly important with irrigated crops. It can help standardize and conserve water, avoiding costly waste. Researchers have found that in cotton crops, for example, normal irrigation planning gives about 55 percent efficiency. Laser leveling, while costly at the present time, improves efficiency to 85 percent. Agricultural engineers report that under this new hi-tech method some crop yields could improve as much as 30 percent.