To many people, no-till farming appears to be a tremendous step forward for agriculture. At a time when fertile topsoil is being worn away by wind and water at rates that are figured in tons per acre per year, a drastic new soil-conservation measure is certainly in order. And as you're about to see, no-till does preserve topsoil, but this advantage doesn't come without certain trade-offs. As it's currently practiced in the U.S., no-till farming might more appropriately be called no-till/chemical agriculture.
In conventional tillage, the earth is turned to a depth of 8 to 12 inches with a plow, most commonly one of the moldboard variety. Subsequently, the plot is disked at least twice more to prepare the seedbed before planting takes place. In no-till, however, the first three steps in conventional cultivation are dispensed with. Planting is done right through the residues of previous plantings and weeds with a device (usually a coulter) that cuts a slot a few inches wide, followed by equipment that places the seeds and closes the trench. There's much more of a difference between these two agricultural techniques than three passes over the field, though, so let's look into the rationale of each method.
Benefits of No-Till Farming
In the first paragraph of the landmark 1943 book Plowman's Folly, Edward H. Faulkner said, "The truth is that no one has ever advanced a scientific reason for plowing." Nonetheless, 40 years after that publication cracked the foundations of agricultural science, most farmers still plow.
The most obvious (or at least the most frequently claimed) reason that soil is tilled is to loosen it so oxygen and water can reach the area where roots will grow. It seems logical that friable, loose earth would allow roots to spread evenly and to proliferate, and this is indeed the case. But using a moldboard plow doesn't necessarily produce such soil. Plowing and disking a field results in a soil with broken structure lying atop a heavily compressed plow pan (the undisturbed layer that the plow doesn't reach). This broken-up soil is very prone to being compacted by rainfall. In addition, many passes must be made over the field with very heavy equipment, the wheels of which further compress the soil. Untilled ground starts off being less compacted than a heavily machine-worked field, and it stays that way. What's more, earth that has become compressed by tillage or machinery will return to a less compacted state after a few years of no-till planting.
Plowing, it is claimed, incorporates fertilizers and crop residues into the soil, making nutrients readily available to the roots of the plants. Turning organic matter under also has the benefit of preventing planters from becoming fouled with surface trash. In no-till farming, crop residues are left on the surface, where the nutrients that result from their decay can leach into the soil. This leaching process is far more thorough than you might imagine. Fertilizers—including anhydrous ammonia, phosphorus, and potassium—are at least as effective on the no-till fields where they've been dispersed as on the plowed plots. And with the right equipment, these ingredients can be placed directly into the planting trench (where they're most needed) during seeding. As for the potential problem of the planter fouling with residues, specially designed no-till planters have a device that cuts a slot through surface trash. Besides, studies have shown that the accumulation of this surface material levels off after a few seasons of no-till practice.
Of course, conventional plowing does prepare a seedbed. No-till farming also does this . . . but in a much more restrained way. In normal tillage, the entire field is turned into a seedbed that may be mounded for planting. With no-till, one simply prepares a narrow trench of the appropriate depth. Studies have shown that plant roots develop at least as well in a no-till field as in a plowed one and that the lack of mounding exposes less of the soil to air and evaporation.
Conventional plowing is also done across the contours of the land to prevent soil erosion. But once again, this rationale doesn't hold up when you look at the results possible with no-till. The crop residues on a no-till field prevent runoff to an amazing extent: On slopes that are steeper than can normally be planted, no-till fields have consistently shown next to no topsoil loss after downpours of several inches per hour. That same vegetative cover also makes the no-till field less susceptible to the effects of wind erosion. This type of agriculture truly offers a solution to the problem of topsoil loss.
A fringe (but certainly not insignificant) benefit of the retention of runoff is that no-till soils stay more moist than those in tilled fields. The surface residues trap water and protect the earth below from the evaporative effect of the wind. In the West, where adequate spring moisture depends largely on snowmelt, the vegetative cover helps keep the snow from blowing away.
The list of environmental benefits that no-till farming boasts over conventional practices goes on and on. But beyond its ability to create a more natural soil that retains nutrients and water, prevents soil erosion, and compacts less, the no-till technique offers a number of immediate financial advantages to the farmer. Not only are the number of trips over the field cut by at least three (thereby saving fuel and wear and tear on tractors), but fewer pieces of equipment are needed. Plows, cultivators, and disk harrows become obsolete. And because the no-till planter can be pulled by a smaller tractor than is required to drag a disk or plow, money can be saved on the size of this piece of equipment, as well.
Yields are generally at least as good with no-till agriculture as they are with plow techniques. Though the soil does stay cooler until a little later in the spring because of the insulating layer of residue, the day/night soil temperature fluctuations are smaller. A no-till field rapidly makes up its deficit in growth rate as the weather turns warm. And if the summer should be really hot and dry, no-till yields will nearly always exceed those of plowed ground. Since soil moisture levels can be more than 10% higher in late July in an unplowed piece of ground, it's not surprising that plants are happier in a field covered with mulch.
In short, the more one looks into the justifications for conventional agricultural practices, the more one realizes that there really isn't much sound defense for tillage.