2.1.1. Type of tillage.

Tillage, particularly conventional plowing, may create a hardpan, or plow sole; that is, a compacted layer just below the zone disturbed by tillage. Such layers are more prevalent with increasing levels of mechanization; they reduce crop yields and must be shattered, allowing water to be stored in and below the shattered zone for later crops.

• Conventional or clean tillage - Up until about 20 years ago, the standard tillage practice for corn was use of the moldboard plow for primary tillage followed by several secondary tillages and mechanical cultivation after the crop was up. Today's farmers have turned away from moldboard tillage because moldboard plows tend to leave minimal crop residue on the soil surface after tillage and in turn, decreases valuable organic matter. By reducing moldboard plow use, and increasing organic matter in the soil, the soil becomes less erodible soil, looser, and holds more water. Today, a very low percentage of row crops are planted with the moldboard plow and mechanical cultivation is often limited to one, or no operations.

Primary tillage. Create a soil condition from which a seed beed can be prepared using secondary tillage implements. Soil disturbance is generally > 6” deep. Primary tillage is necessary when existing soil conditions prevent the effectiveness of secondary tools. Moldboard and disk plows invert the soil in a plow layer, resulting in the burial of most crop residues. Aggressive tine tools such as chisel plows, rippers and subsoilers fracture soil but do not invert soil and retain more residue cover. Aggressive rotary powered tools, such as spaders and rotary tillers, can be used for primary tillage. An acceptable seed bed can sometimes be prepared in only one pass.

Secondary tillage. To improve seedbed preparation – may involve increased soil pulverizing, leveling, and/or residue sizing and burial, to conserve moisture through destruction of weeds, and to cut up crop residues, is accomplished by use of various types of harrows, rollers, or pulverizers, and tools for mulching and fallowing. Soil preparation is traditionally full field but can be concentrated in row zones. Tillage tools used for seed bed preparation are generally referred to as “harrows”. Most harrows are draft implements with gangs of tines, disks, rolling baskets or combinations. Powered harrows (e.g. rotovators, rod weeder, reciprocating harrow) are also used for seed bed preparation and can accomplish more in one pass than draft tools. There are five principal types of harrows: the disk, the spike-tooth, the spring-tooth, the rotary cross-harrow, and the soil surgeon. Rollers, or pulverizers, with V-shaped wheels make a firm and continuous seedbed while crushing clods. These tools often are combined with each other. Used for stirring the soil at comparatively shallow depths, secondary-tillage equipment is generally employed after the deeper primary-tillage operations; some primary tillage tools, however, are usable for secondary tillage.

• Reduced tillage is usually done with a chisel plow and leaves 15% to 30% residue coverage on the soil. Reduced tillage refers to any system that requires less soil manipulation than a conventional systems used for comparison. The reduced tillage objective saves tractor fuel and time when unnecessary, unproductive tillage operations are eliminated. Combining operations into a once-over trip, strip tilling only the planned rows, and tilling only as deep as is productive are actions to reduce tillage energy and ultimately the cost of production. Chemical weed control may be required.

• Conservation tillage is a term introduced in the 1980’s and refers to a range of reduced tillage systems with no-till (or zero till) being the extreme. By definition, conservation tillage systems leaves at least 30% or more crop residue coverage on the soil surface after planting or at least 1,100 kg/ha of small grain residue on the surface during the critical soil erosion period. On highly erodible soils, conservation tillage procedures are necessary. The objectives include reduction of both wind and water erosion. Maintaining a soil cover with previous crop residues or producing a soil surface of dense clods meets this objective. Weed control is dependent on chemical herbicides. Conservation tillage objective are met by a broad range of tillage systems, including the below:

no-till (or zero till), where no tillage is done at all and seeds are placed directly into the previous season's crop residue. No-till involves minimal soil disturbance with the crop planted directly into stubble from the previous crop. The seeding machine crates a narrow, tilled strip for receiving the seed.

strip-till, in which only the narrow strip of land needed for the crop row is tilled; ridge till; and mulch till.

Herbicides might be used in all these methods to kill weeds. In no-till systems, the herbicide is applied directly on last season's crop residue. In the other methods, some soil preparation takes place before the herbicide is applied. A common myth is that more herbicide is used with conservation tillage methods, but in fact farmers rely on herbicides for weed control under all tillage systems, and the amount used is more or less independent of tillage method.