Raelani Kesler SOIL 501: Winter term 2020

A false or stale seed bed is a cultural practice used in agriculture to control annual weed pressure. A succession of weeds from the soil seed bank is germinated and terminated before a crop is planted. This is achieved by clearing the ground, normally by tillage or occultation, and then allowing weeds to germinate. Weeds are let grow until only a couple inches tall, when they are eliminated by means of tillage, occultation, flame weeding, or solarization. Stale seed bedding is especially effective because most weeds germinate from the tops 2.5 inches of soil^[1] , thus this technique reduces the number of weeds set to germinate after a crop has been planted. Weed emergence depends on the weed species, soil type, soil characteristics, and prior land management practices^[1] .

This technique is popular amongst growers for its capacity to improve farm efficiency during harvest and cultivation events^[2] . It can be utilized as a part of a farm scale zero weed tolerance system in which no annual weeds are allowed to set seed. This method has proven to drastically reduced weed pressure over three to four years^{[3] [2]} . Stale seed bedding is a cultural practice especially useful in the spring when fields or gardens are being returned to food production from a winter fallow or cover crop. However, there remain many uses for stale seed bedding throughout the growing season when managing succession plantings. Temperature, light hours, and moisture all directly affect germination of seeds, often the duration of a stale seed bed cycle is related to such climatic factors. Weeds are most easily managed when they are at or before thread stage, when plants are approximately less than two inches and have undeveloped and shallow root systems. Generally, weeds should be terminated before developing any true leaves during its cotyledon phase. When annual weeds are terminated before setting seed, subsequent weed flushes will be lessened. Stale seed bedding is used in a wide range of agricultural systems and with a variety of different crops. The methodology employed depends on the size of the seed bed, soil, climate, and crop type amongst other variables.

Adapted from UC Davis^[4]

1. Clear ground.
2. Irrigate or allow rain to germinate weed seeds.
3. 7-10 days after being watered, terminate weeds.
4. Repeat steps 2 and 3 as needed and time permits.

Tillage may be used to both initially prepare a seedbed and to terminate germinating weeds. Tillage kills weeds by burying them, cutting up biomass, and exposing roots to air. Initial tillage to return a field into production after the winter first plant biomass that accumulated over the winter, including weeds. This tillage also introduces air and light to surface soils, creating an environment favorable for the emergence of spring weeds^[2] . The time between initial tillage and the termination of the sprouted weeds depends most directly on soil moisture and temperature. Care should be taken when using tillage to terminate emergent weeds, the mixing and churning effect of implements such as a rototiller or disk may bring seeds from deeper soil layers to the surface, increasing weed presence^[3] . Decreasing the depth of tillage is the primary alleviation of this risk. This requires careful timing, in order for shallow tillage to effectively terminate weeds they must be small and shallowly rooted. Tillage depth at the time of weed termination should be shallower than the time of ground clearing to avoid bringing new weed seeds to the surface^[2] . Depth of tillage may be lessened by using tillage Implements that spin along a horizontal plane, such as the rotary harrow. Utilizing lightweight or hand-scale tillage implements may also reduce depth of tillage, options range from walk behind tractors to hoes. The use of tillage to create a stale seed bed in the spring is dependent on soil moisture. Depending on the soil type and climate, some soils may become saturated in the spring, inhibiting the use of a tractor. When soil is worked at a high soil moisture content, the tillage deteriorates the soil structure and causes subsurface compaction, both negatively impacting soil health.

Occultation and solarization are related techniques that may be used to create a stale seed bed. Occultation is the process of killing weeds by inhibiting photosynthesis, commonly a black or opaque tarp is used to deprive plants of sunlight^[5] . Dark, impermeable tarps warm soil and hold moisture. In this environment more seeds germinate and perish under the tarp deprived of sunlight, killing both existing weeds and further depleting the surface soil seed bank. Under tarp conditions may also promote decomposition of organic matter by simulating soil biota.

Solarization is the use of a clear tarp to increase temperatures to inhospitable levels for the germinated weeds and is only effective again small annual weeds^[5] . Opaque tarps can be used to both clear ground and to eliminate weed flushes before planting while transparent tarps are only used to terminate weeds. It is also possible to combine either technique with tillage; the ground may be initially cleared by tillage, weeds germinate with the aid of precipitation or irrigation, and then tarped until the weeds have died.

The length of time necessary for the ground to be covered depends on the weeds present. In the case of occultation, small annual weeds will perish quickly while perennial or rhizomatous weeds will take longer to expend their energy reserves or may be able to survive this method. The timescale of stale seed bedding does not lend well to the eradication of perennial weeds, separate weed management strategies are necessary. However, occultation methods have been used to reduce reliance on mechanical tillage which can lead to the decreased occurrence of some perennial weed species^[5] . In no-till vegetable systems occultation can be used to terminate overwintering cover crop in the spring, the tarps removed and then reapplied when weeds have germinated, coupling the eradication of a spring weed flush with the decomposition of cover crop biomass. Bulk density and compaction should be monitored in such systems.

Flame weeding use heat to kill young weeds. The heat from the flame expands the liquid in plant cells until the pressure is enough to break the cell walls ^[3] . Flame weeders are often powered by propane, most basically a flame weeder consists of a fuel tank connected to hose with a torch wand. Tractor mounted models are available, as well as hoods for hand held flamers to concentrate the heat. Flame weeding is most effective on flat, sodless ground. Annual weeds less a few inches tall are easily terminated, however, flaming is ineffective against grasses and most perennial weeds. Pre-emergence flaming involves direct seeding crops into the field, allowing weeds to germinate, and flame weeding before the crop seeds have germinated. The timing for flaming varies from 3-14 days after seeding depending on the crop species. Flame weeding may also be utilized to create a stale seedbed when the ground is too wet to cultivate.

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A false or stale seed bed is a seedbed created some weeks before seed is due to be sown. The early seedbed is used a weed control technique. It is designed to germinate weed seeds that have been disturbed and brought to the soil surface during cultivation, so that the young weeds can then be eliminated. The tilled soil increases the chance of weed seed germination as the fine soil allows seeds to grow more rapidly than in compacted soil and dormant seeds are brought to the surface. The weeds must then be destroyed before they can create new seeds. By destroying them early, the farmer eliminates most of that season's annual weeds, and nominally increases soil nutrient content.

The technique can be utilized in early spring, when the weather is still too cold for proper seed germination. Several passes are made with a power harrow, such as an R2 Rinaldi, rototiller or plow, then weed seeds are allowed to germinate as weather permits. By tilling, the farmer increases the chance of weed seed germination by the same method as one would for favorable vegetable/crops: the fine soil allows weed seed to grow rapidly by allowing the seed to open and the roots to spread easier than in compacted soil. Deep tilling will also bring dormant seed to the surface for germination; some species of plant are known for seeds that can lay deeply buried in the soil for years before favorable conditions allow germination.

After weeds have sprouted, they are hoed off or eliminated with the other means (e.g., use of a flame weeder) before sowing of the actual crop. Timing is important; weed seeds must be destroyed before they themselves can create new seeds. By destroying them early, the farmer eliminates most of that season's annual weeds. Turning the dead weeds back into the soil also increases soil nutrient content, although this difference is slight.

In many cases, several tillings are done, perhaps every two weeks beginning in very early spring. This allows more and more weed seeds to germinate only to be killed off later. This eliminates more weeds, but care must be used to not delay planting of a desirable crop later than the crop needs for a successful season's growth. After several years, most, if not all, weeds can be eliminated from the seed bank in the soil. In some cases the effect can be noticed in the same year the process is first carried out.

A stale seed bed technique of weed control creating a seedbed some weeks before seed is due to be sown. The early seedbed is designed to germinate weed seeds that have been disturbed and brought to the soil surface during cultivation, so that the young weeds can then be eliminated before they can propagate.

If the weed patch is vigorous enough, the farmer may mow the patch first before tilling. This allows for easier/quicker decomposition in the soil when the plants are turned under. Some farmers may apply a light and inexpensive fertilizer mix to the soil to hoping to cause even more weed seeds to germinate and eliminate seeds earlier that otherwise would have sprouted in later years.