Soil type and previous cropping pattern dictate the amount of tillage necessary to prepare the seedbed. A field with a large amount of residue from the previous crop, such as a crop produced on irrigated soil, requires deep plowing or deep tillage to help decompose the residue and to keep the surface soil free of debris. Soil should be plowed ordisked as deeply as possible to help break up compaction and reduce the risk of herbicide carryover. Deep plowing, or at least twodiskings, may be necessary.Disking and harrowing follow plowing orchiseling to complete seedbed preparation.Small Grain Production Manual
Soils should not be tilled when wet since this contributes to soil compaction, large clods, and other physical conditions unfavorable for growth of small grains.
The seedbed should be several inches deep, and the soil clods should be small enough so that they do not interfere with grain drilling, such as by getting caught between disc openers. Seedbeds with large clods and heavy crop residue that do not pass freely through the conventional 6- to 7-inch drill spacing of grain drills produce a weak stand with uneven germination. Conversely, an overprepared seedbed creates a powdery surface soil that is prone to crusting, which can delay or prevent emergence. Seedbed preparation for broadcast seeding is less critical because the broadcasting equipment does not drag clods and residue.
Summer fallowing preceded by deep plowing or deep tillage is one system used in rainfed production areas. With summer fallowing, seedbed preparation can be com- pleted well before the normal fall planting period, allowing seed to be planted before the onset of the rainy season. Seedbed preparation for summer fallowing begins with plowing or chiseling in spring followed by disking or harrowing. This process starts after volunteer cereals and weeds have made some growth but before weeds have pro- duced seed and while there is ample moisture available for tilling. Soil can then be disked in early fall to break up large clods and harrowed after the first rain to help control germinating weeds.
Annual cropping is also used in rainfed areas. Seedbed preparation for annual rainfed cropping begins with disking or chiseling dry soil in early summer. The seed- bed is prepared after fall rains begin and is completed with shallow disking or harrow- ing. There is more risk of crop failure with annual cropping than with summer fallow- ing because inadequate moisture conditions and increased weed and disease pressure are more likely under annual cropping.
minimum-Till and no-Till
Minimum-till and no-till seedbed preparation can be very beneficial inrainfed crop- ping systems because the crop residue that remains on the soil surface helps retain moisture and prevent soil erosion. In addition, reduced-tillage systems generally have lower input costs than conventional systems. Seedbed preparation usually consists of applying chemical weed control if weeds are present and drilling seed directly through the residue of the previous crop. The amount ofdisking and harrowing needed to bury surface crop debris, kill emerging weeds, and incorporate seed or fertilizer is limited. Straw and chaff must be thoroughly chopped and spread during harvest of the previous crop in order for sowing to be successful. Also, care must be taken in setting up sowing equipment so that the drill is able to cut through surface residue. “Hairpinning” occurs when residue is not cut but stuffed into the seed slot by the openers, preventing the soil-seed contact necessary for optimal germination.
Mulch may be used in irrigated production in the Southern California Desert Region or other regions where rain is not expected before stand establishment. Fields are pre- pared, leveled, fertilized, and irrigated approximately 2 to 4 weeks before sowing to allow enough time for the fields to dry sufficiently for mulching and seeding. A mulch layer of dry soil 2 to 3 inches (5 to 7.5 cm) thick is created and seed is drilled into
the moist soil beneath the mulch layer. This system of mulching can provide excellent weed control.