Major Data: Soil left fallow, or unplanted, is not only a missed opportunity to plant carbon-fixing biomass but management that constantly exposes soil to harsh natural elements. Wind, rain, heat, and other extreme environmental conditions lead to: erosion, topsoil loss, surface sealing, nutrient loss, poor SOM, low cation exchange capacity, and poor microorganism populations. Together, these processes can destroy soil aggregates, releasing soil organic carbon into the atmosphere (Rodale Institute, n.d.).
Ultimate Driver: Leaving soil fallow began as a practice 2,000 years ago in the Roman Empire. Roman farmers used a system called "food, feed and fallow"; one third of farmland was used for a food grain, one third for livestock feed, and one third lay fallow. The intention was for the section in fallow to "rest" and have enough time to naturally replenish SOM and nutrient stores. This practice influenced American farmers when it was popularized in part by George Washington Carver in the form of crop rotation (Hanson and Duncan, 2014).
Proximate Driver: In the 1950s and 60s, herbicides were rapidly adopted by farmers. This radically reduced the use of hand weeding and cultivation which reduced labor costs and time while increasing yield (Gianessi and Reigner, 2007). As a result, it became more economically viable to keep fallow fields bare with the use of herbicides instead of letting weeds grow and investing the time and money to remove them when taking the field out of fallow.
Current Solution: Cover crops are an effective tool for establishing soil cover while crowding out weed species (Pimentel et al., 1997).
Current Solution: Farmers practicing adaptive, multi-paddock grazing (AMP) or other forms of roational grazing utilitze livestock for weed and cover crop management (as opposed to herbicides). Livestock graze and trample the cover crops or weeds before they go to seed, preparing the land for seeding by creating a layer of mulch (Brown, 2018).
Proximate Driver: If weeds are left undisturbed on fallow soils they have the potential to go to seed and establish their weed seed bank in the soil. When weeds develop their seed bank farmers can kill a large majority of the seeds but the weed pressure will still be great because of how many seeds initially fell to the ground (Grubinger, 2010). This is a case for herbicide use to again reduce management and labor costs in bringing a field out of fallow.
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Proximate Driver: It is estimated that the overall cost to plant a cover crop such as cereal rye in between plantings of corn and soy costs $20.60 per acre. While this may not seem incredibly costly, a farmer may be deterred by the price if there is no market for the crops and no opportunity to break even. Additionally, if the growing season of the cover crop is too closely overlapped with that of the cash crop it may not be worth it to seed a cover (Schnitkey et al., 2016).
Potential Solution: One idea is to create a mainstream market for cover crops so that farmers can afford to take their fields out of rotation. Patagonia Provisions is beginning to popularize this idea by partnering with farmers who grow pacific northwest buckwheat, barley, kernza, and green lentils. These crops are grown between cash crops which aid in giving the farmers a source of income in the off-season, an incentive to not leave their fields in fallow, and a ecologically sound way to reduce weeds, decrease erosion, increase SOM & SOC, and increase water holding capacity (Patagonia, n.d.).
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Current Solution: The cultivation of perennials can reduce erosion by nearly 50% (Pimentel et al., 1997).