| Soils, Crops and Fertilizer Use |
|Chapter 4: Seedbed preparation|
Tillage can either enhance or destroy good soil filth (workability). Sure, plowing and harrowing break up clods and loosen the topsoil, but the stirring and shearing action stimulate the microbial breakdown of beneficial soil organic matter and may also overpulverize the soil. Tractor wheels, animal hooves, (and even foot traffic) can cause soil compaction (especially on wet, clayey soils), which can seriously impair root growth and drainage. In mechanized farming, it's common for a traffic pan (compacted zone) to develop on many soils (even sandy ones) at a point right below tillage depth. Plowing clayey soils when they are overly dry can produce large, brick-hard clods that may first require rainfall or watering before they can be broken up. Tilling clayey soils when they are wet can seriously affect their their filth.
The two implements most likely to harm filth are the disk harrow and the rototiller. Many farmers overuse the disk harrow by making repeated passes to kill weeds or smooth the soil. Unfortunately, harrowing kills one stand of weeds but encourages another by bringing up more weed seeds closer to the surface where there is sufficient oxygen to trigger germination.
The Ideal Seedbed
The only portion of the seedbed that needs to be reasonably clod-free is the narrow row zone where the seeds are planted. In fact, you're actually better off keeping the spaces between the rows in a cloddy condition to discourage weed germination and help maintain filth. Since the 1960's, minimum tillage systems such as plowing and planting in one operation or using specially designed planters to plant directly through crop residues into unplowed ground have become increasingly popular for field crops like maize in the developed countries. These methods have definite potential for the Third World, too. For example, the International Institute for Tropical Agric. (IITA) in Nigeria has been adapting such reduced tillage methods to small farmer conditions (see address in Appendix G). They have developed hand-pushed planters that can successfully plant maize and cowpeas through vegetation that has been slashed down (or killed with a herbicide) and left on the soil surface as a beneficial mulch. No tillage is used with this method.