|Soils, Crops and Fertilizer Use: A Field Manual for Development Workers (Peace Corps, 1986, 338 p.)|
|Chapter 4: Seedbed preparation|
Seedbed "fineness" refers to the degree to which clods are broken down and the soil smoothed over. The need for this depends mainly on seed type, seed size, and whether hand planting or mechanical Planting will be used.
Seed type: Monocot plants like the cereals (maize, sorghum, etc.) have one cotyledon (seed leaf) and break through the ground in the shape of a spike which helps them handle some cloddiness. Dicot plants (pulses like beans, cowpeas, peanuts, and virtually all vegetables) have 2 cotyledons and emerge from the soil in a much more blunt form, actually dragging the 2 seed leaves (formed from the 2 halves of the seed) with them. They have less clod-handling ability than most monocots, although seed size also makes a difference.
Seed size: As a rough rule, the larger the seed, the less the need for a fine seedbed. Large seeds have more energy and can also emerge from greater depths. A seed like maize is not only large but is a monocot too, so it has especially good clod-handling ability. Peanuts, beans, and most other pulses are large seeded, but this advantage is partly offset because they are dicots. The small seeds of millet and sorghum lack some power, but being monocots is a help. Note that smaller seeds (i.e. lettuce, cabbage, onions, amaranth, require shallower planting than larger seeds (i.e. pulses, okra, maize, squash, etc.) and that a cloddy seedbed makes it difficult to be precise with planting depth.
· Hand vs. mechanical planting: Farmers who hand plant can usually get by with rougher seedbeds for several reasons. It's easier to control planting depth when hand seeding and large clods can be pushed aside. Also, it's common under hand planting to plant several seeds per hole, which provides more power for breaking through the soil.