The origins of strip farming can be traced to the enclosure movement of post medieval Great Britain. Landlords consolidated the small, fragmented strips of land farmed by tenant peasants into large block fields in an effort to increase agricultural production.
Peasant plots were typically 1 acre in size: 220 yards, or one furlong in length (the distance a team of oxen can plow before resting) and 22 yards in width (the amount one team of oxen can plow in one day).
After enclosure, fields were 100 or more acres in size. Larger fields were more productive but were also more exposed to wind and water erosion and nutritional exhaustion.
As agricultural production gradually shifted to new lands in the Americas and colonial Africa, farmers continued to use large-field farming techniques and developed large-field plantations. By the early twentieth century, all readily tilled lands had been opened by the plow and were suffering the effects of water and wind erosion.
Strip farming, also known as strip cropping, was developed as a soil conservation measure during the 1930’s. During the 1960’s strip farming became an important tool to prevent water and air pollution and improve wildlife habitat.
Wind erosion begins when wind velocity at 1 foot (0.3 meter) above soil level increases beyond 13miles (21 kilometers) per hour. Saltation and surface creep also allow soil to move. In saltation, small particles are lifted off the surface.
These articles travel ten to fifteen times the height to which they are lifted, then spin down ward with sufficient force to dislodge other soil particles and break earth clods into smaller particles. Surface creep occurs when particles too small to be lifted move along the surface in a rolling motion.
The wider the field, the greater the cumulative effect of saltation and surface creep. These factors can lead to an avalanche of soil particles across the widest fields even during moderate wind gusts.
Water erosion begins when raindrops or flowing water suspends soil particles above the surface and transports them down-slope by splash or runoff.
Ice crystals expand, then contract when melted, dislodging soil particles and making them available for both water and wind erosion. Water also leaches nutrients and chemicals from the soil, causing the soil to experience both nutrient loss and an increase in salts and acids.
The U.S. Department of Agriculture computes annual soil loss from agricultural and developed land using the formula A = RKLSCP.
In this formula, A equals annual soil loss, R equals the amount of rainfall on the plot, K equals the erosion factor for the type of soil on the plot, L equals the length of the slope on which the plot is located, S equals the angle of the slope, C equals the type of crop or soil cover on the plot, and P equals the presence of management conservation practices such as buffers, terraces, and strip farming. Soil loss tolerances are calculated for each plot. The tolerance is the amount of soil that can be lost without reducing productivity.
Loss tolerances range from1 to 5 tons per acre per year. Farmers and developers reduce soil losses to tolerance levels by reducing soil exposure to wind and rain and by utilizing conservation practices, such as strip farming.
Crops are arranged so that a strip of hay or sod (such as grass, clover, or alfalfa) or a strip of close-growing small grain (such as wheat or oats) is alternated with a strip of cultivated row crop (such as tobacco, cotton, or corn).
Rainwater runoff or blown dust from the row-crop strip is trapped in this way as it passes through the subsequent strip of hay or grain, thus reducing soil erosion and pollution of waterways. Contour or field strip cropping can reduce soil erosion by 65 to 75 percent on a 3 to 8 percent slope.
Cropping in each strip is usually rotated each year. In a typical four-strip field, each strip will be cultivated with a cover crop for one or two years, grain for one year, and row-crop planting for one year.
Each strip benefits from one or two years of nitrogen replenishment from nitrogen-fixing cover crops, such as alfalfa, and each strip benefits from one year of absorbing nutrient and fertilizer runoff from the adjacent row-crop strip.
Strip widths are determined by the slope of the land: the greater the slope, the narrower the strips. In areas of high wind, the greater the average wind velocity, the narrower the strips. The number of grass or small-grain strips must be equal to or greater than the number of row-cropped strips.
Terraces are often constructed to reduce the slope of agricultural land. At least one-half of the land between each terrace wall is cultivated with grass or a close-growing crop. Diversion ditches are often used to redirect water from its downhill course across agricultural land.
These ditches usually run through permanently grassed strips, through downhill grass waterways constructed across the width of the strips, and through grassed field borders surrounding each field.