Ways to Till the Soil

by F. L. DULEY and O. R. MATHEWS

FOR CENTURIES the plow has been the basic tool and symbol of farming. Men in all ages have worked hard to develop it and ways of using it to kill weeds and prepare the ground for planting. The ancients used a crooked stick and primitive peoples in some parts of the world still use a wooden implement, which does considerable breaking and loosening of the soil without burying deeply the organic material on the surface. In more recent times the modern steel moldboard plow has been evolved, and now there is a sharp questioning of the value of plowing too well—perhaps the ancients had a point, after all.

For centuries people have observed that clean-tilled land, free of vegetation, loses more soil by erosion than stubble land or land covered by growing vegetation. But the wisdom of using the moldboard plow and other implements that leave the land bare went almost unchallenged until the second decade of this century. Experiments at the Missouri Agricultural Experiment Station then showed that more runoff takes place and much greater erosion occurs on bare cultivated land than oil land protected by a growing crop, particularly grass.

Various tillage methods have been used in an attempt to reduce water erosion on clean-tilled land by reducing runoff. Plowing, especially listing, and seeding on the contour, have been of some help. Constructing -small dams in lister furrows by means of a damming attachment was tried as a means of holding more of the water on the land and avoiding the necessity for contour cultivation. The method has not been widely accepted because the dams may not hold unless the work is done on an approximate contour. If done on the contour it has little advantage over ordinary listing and is more expensive.

Another way to impound water on the soil is to use various types of pitting implements that leave shallow holes or pockets on the surface; the pockets reduce runoff, but when they are filled with water or washed-in soil, their effectiveness is destroyed. The difficulty of obtaining weed control while maintaining pockets on the surface is another reason why the practice has not been more widely adopted.

Clean tillage is a major cause of wind erosion. This is especially so in the Great Plains, where the highest average wind velocities occur in the late winter and early spring when the soil is most likely to move. Tillage that brings clods to the surface or that roughens the surface can protect the soil for a temporary—but only a temporary--period. In dry-land areas soil must be cultivated when no crop is growing in order to destroy weeds and conserve moisture for the following crop.

Effect of Residue on Runoff and Erosion

Research in Nebraska has shown that tilled land that has the dead residue from the previous crop remaining on the surface has a higher rate of infiltration and retains it longer than bare tilled soil or soil where the residue has been partly buried by disking or one-waying. When raindrops strike bare soil, the structure particles are broken and the surface is sealed over; this compact layer, often less than an eighth of an inch thick, may become slick on the surface. It then reduces the rate of infiltration and increases runoff. Residue over the surface prevents the raindrops from striking the bare soil and allows the water to trickle down gently through the mulch. The surface structure remains intact and a high rate of infiltration is maintained. The stability of the soil structure may affect the time during which water may seep down through it before the infiltration rate is greatly lowered. If the soil becomes fully saturated and has heavy layers in the subsoil, the rate of infiltration may be limited by soil conditions below the surface, and then the intake is not so greatly affected by surface residue.

Along with the reduction of runoff there is a consequent reduction of water erosion. In fact, a stubble mulch is relatively more effective in reducing erosion than in reducing runoff. A considerable quantity of water can run over a mulched surface without carrying much soil.

Leaving crop residue on the surface also has had a marked effect in reducing wind erosion. Undecayed straw or other residue that is well distributed over the surface will reduce the wind velocity at the surface, so that particles of soil are less likely to start to move. If they do start to move, the residue provides places where the particles may lodge. Moving particles may also strike residue material and have no abrasive effect.

The effect of crop residues on soil blowing has long been recognized. As early as 1915 the Department, in a bulletin discussing tillage in eastern Colorado, directed attention to the fact that a smooth, well-harrowed surface was subject to soil blowing and that stubble left on the field might help to catch snow and prevent the soil from blowing.

The adoption of fallowing as a farm practice in the Great Plains was greatly hampered by the wind-erosion hazard that it created. Efforts to control wind erosion by tillage that kept the surface in a cloddy or roughened condition were reasonably successful on some soils, but not on others. Plowless fallow experiments, where the land was cultivated with implements like the duckfoot or field cultivator that left much of the residue on the surface, were started in the early 1920's. They demonstrated that residues were valuable in preventing or reducing wind erosion, and that the expensive operation of plowing was not essential in fallowing operations. That plowing was not needed regularly in the production of small grains in that area had already been demonstrated. In the Columbia River Basin, where fallowing has been an established practice for many years, soil blowing on the lighter soils led to the adoption of such implements as the plow without a moldboard for controlling erosion. This implement stirs the ground deeply without completely turning it.

Tillage implements differ in the depth to which they stir the soil, their effectiveness in killing weeds, the position in which they leave the crop residue, and in their cost of operation. The advantage of one tillage method over another may not be so much the depth or extent to which it stirs the soil as the position in which it leaves the crop residue.

So far, four methods have been used in the disposition of crop residues: Removed from field or burned, completely turned under by plowing, partly buried by disking or some similar operation, and left entirely on the surface by some method of subsurface cultivation. The first three are well known to most farmers; the fourth is newer.