Synthetic nitrogen-based fertilizers were made possible because of the Haber-Bosch process, which converts stable, inert nitrogen gas unavailable to plants into the reactive ammonia molecule readily available for plant uptake. Once the process was commercialized, synthetic fertilizer use skyrocketed, as farmers were no longer dependent only on their soil organic matter, compost, cover crops, and livestock manure for nitrogen. Fertilizer use in the United States increased from about 7.5 million tons in 1960 to 21 million tons in 2010. In 2007, California farmers applied 740,00 tons of nitrogen in fertilizers to 6.7 million acres of irrigated farmland. With cheap sources of nitrogen and water available, our current agricultural system is based on the liberal application of synthetic fertilizers and irrigation water to ensure high yields, often at the expense of environmental and public health. California’s Central Valley is home to some of the most heavily fertilized cropland and some of the most polluted water in the United States. Communities there are particularly vulnerable to public health effects of nitrate contamination because groundwater provides drinking water for the majority of residents. Additionally, rural communities in the valley are generally poor and populated by immigrants and minorities least able to afford treatment costs and most vulnerable to discriminatory decision-making. Tulare County, the second most productive agricultural county in California, includes many of these communities. Though it generates nearly $5 billion in revenue from agriculture each year, it has the highest poverty rate in California and is populated mainly by minorities , most of whomare Latino. The average per capita income in the county is $18,021. Here, indoor cannabis growing one in five small public water systems and two in five private domestic wells surpass the maximum contaminant level for nitrates.

As a result, residents of towns like Seville, East Orosi, and Tooleville are paying $60 per month for nitrate-contaminated water they can’t safely use, and must spend an additional $60 to purchase bottled water for drinking and bathing. In contrast, San Francisco water customers pay $26 per month for pristine water from the Hetch Hetchy water system in Yosemite. The economic cost of nitrate contamination in drinking water is not the only cost to these communities. Farm workers make up a significant segment of the population of small towns throughout the Central Valley and are both directly exposed to the hazards of heavy fertilizer use in the fields and in the air, and through excess nitrogen leached into groundwater drinking supplies. Scientists estimate that 50–80% of nitrogen applied in fertilizer is unused by plants. Of that, about 25% volatilizes into the atmosphere . As a result, approximately 30–50% of nitrogen applied in fertilizer—about 80 pounds per acre in California—leaches into groundwater beneath irrigated lands and into public and private water supplies.13 High nitrate levels in water can cause a number of health problems, including skin rashes, eye irritation, and hair loss. More severe is “Blue Baby Syndrome” , a potentially fatal blood disorder in infants caused by consumption of nitrate-contaminated water. Direct ingestion, intake through juices from concentrate, and bottle-fed infant formula are all potential threats to children. Nitrate contamination has also been linked to thyroid cancer in women. Widespread contamination of groundwater through leached fertilizer has rendered drinking water in rural communities across the country not only unusable, but dangerously so. While nitrate contamination is an acute problem in California, it exists across the country. The EPA estimates that over half of all community and domestic water wells have detectable levels of nitrates. Rural communities that rely on private wells , or lack access to adequate water treatment facilities, have the most insecure water supplies. In the short term, municipalities must devise a plan to reduce the disproportionately high cost of water to these communities.

One potential solution is a fee attached to the purchase of fertilizer used to subsidize water costs for communities with contaminated water. Communities with contaminated water could also be added to a nearby water district with access to clean water. In the longer term, the obvious solution is to substantially reduce synthetic fertilizer and water use in agriculture. Treatment, while effective on a small scale, cannot keep up with the vast quantities of nitrates continually entering groundwater supplies through fertilizer application. Similarly, reduced irrigation on farms, drawn mostly from uncontaminated sources, frees up new sources of drinking water for nearby communities. Lastly, to reach a truly sustainable and equitable system of water distribution, residents of rural communities must be included in the planning and decision-making process as members of local water boards, irrigation districts, and planning commissions to establish and safeguard their right to uncontaminated water.Currently, there is mounting evidence that suggests sustainable agriculture practices, exemplified by those used in agroecological systems, provide an opportunity to achieve the dual goals of feeding a growing population and shrinking agriculture’s carbon footprint, in addition to the social benefits of increased food security and stronger rural economies. This is in contrast with industrial-scale conventional systems that rely on fossil fuel-based fertilizers, pesticides, and heavy tillage and look to genetic engineering to help plants cope with climate change, e.g. by developing drought-resistant crop varieties, which themselves require high inputs of fertilizers and pesticides to produce optimally. Agroecological systems, on the other hand, can mitigate climate change by reducing fossil fuel use, and employing farming techniques that reduce GHG emissions by sequestering carbon in the soil. Of the range of practices in an agroecological system that address issues related to climate change, cover cropping is perhaps the most effective. As climate change continues to affect weather patterns and cause more frequent and severe weather events, protecting against soil erosion will become increasingly important. Cover crops provide an effective mitigation strategy by protecting soil against wateror wind-driven erosion. Cover cropping also provides other climaterelated benefits, including: an on-farm source of fertility, less dependence on fossil fuels and their derived products, and adaptability and resilience. Most of all, while the specific species, timing, and primary purpose of a cover crop vary geographically, the principles behind their cultivation are universally applicable and their benefits universally available. The use of a leguminous cover crop to fix nitrogen in the soil over the wet season for the next season’s crop is widely recognized as an effective fertility management tool. According to an FAO report on agriculture in developing countries, using cover crops in a maize/pigeon pea rotation led to increased yields and required less labor for weeding than continuous maize cropping systems with conventional fertilizer use.3 Nitrogen-fixing cover crops also greatly reduce, and in some cases eliminate, reliance on off-farm sources of fertility, thus reducing the overall carbon footprint of the farm while maintaining high fertility levels in the soil. Note that even organic fertilizers have a high embedded energy cost as they are mostly derived from manure from animals raised in confined feedlots, so the ability to grow one’s fertility needs on farm is important across different agricultural systems. Cover crops are not only a mitigation strategy for climate change, but also a cost-saving measure. Synthetic fertilizer costs have steadily increased over the last half-century, cannabis growing supplies causing hardship for farmers in developing countries especially where fertilizer prices are already two to three times the world price. Organic farmers are less vulnerable to price shifts in fertilizer, but can equally benefit from the reduced need for compost as a result of cover cropping. By saving seeds from their cover crops, farmers can close the loop in their cover crop management, save on annually purchased seed, and develop strains well-adapted to local conditions.

Fertility management systems based on cover crops insulate conventional farmers from increasingly frequent spikes in fertilizer prices and provide organic farmers with a cheap and renewable source of fertility. Adaptation and resilience are also crucial to farmers’ long-term success in the face of unpredictable and disruptive effects from a changing climate because so much of agriculture depends on constantly changing climatic conditions. Added to climate change are increasing input prices and a growing demand for food that put pressure on farmers to maintain high yields while paring down on costs. Cover crops can provide farmers with the flexibility they need by protecting topsoil from wind and water erosion, storing a reliable supply of nutrients to the soil, and—if managed correctly— minimizing costly weeding requirements. For many resource poor farmers who maintain livestock, cover crops provide a path to financial independence and food security as they can be grown both for soil fertility and livestock feed. Cover crops as part of a climate mitigation strategy also make sense at every scale of agriculture. Large conventional farms require consistently high yields to stay profitable as they often operate on razor thin margins. To achieve this goal, these farms rely heavily on fossil fuel-based sources of energy and fertility. Whether used on conventional or organic farms, cover cropping not only reduces farm emissions, but also contributes to the biological health of the farm’s aggressively cultivated soils. Many organic farms at all scales already use cover crops as part of their fertility management program, contributing to the sustainability of the overall system. Subsistence and small-scale farmers in developing countries who do not already practice cover cropping can benefit greatly in production and climate-related sustainability from adopting locally relevant techniques. And finally, low-cost, locally available sources of fertility are vital to the viability and success of urban agriculture projects that rely on cost minimization and closed-loop systems since external resources are not as readily available or economical in cities.In areas of the Central Coast where winter rainfall typically exceeds 25 inches per year, and especially on sloped ground, cover cropping in annual vegetable cropping systems is highly advisable to protect non-cropped soil from both erosion and nutrient leaching. Based on numerous studies, the optimum time for planting winter cover crops on the Central Coast is mid October. In our mild winter climate we can plant cover crops as late as January, however the best results in terms of weed suppression, stand uniformity, and biomass production are from cover crops planted in mid to late October or early November. Depending on rainfall patterns it is often critical to get winter cover crops planted prior to the onset of heavy winter rainfall. Cover crop ground preparation and planting are best accomplished when soil is dry enough to work without the risk of compaction, which can result in poor drainage and clod formation. This is especially important on heavier soils. Because timing is critical, growers need accurate long-range weather forecasts to help determine when to prepare ground and plant fall cover crops. Timing these operations is directly related to soil type and rainfall amounts, so each farm will have a different set of criteria on which to base ground preparation and planting schedules: the heavier the soil and the greater the rainfall, the tighter the window for fall planted cover crops. There is often a very tight window between cover crop planting and harvest of fall crops which, coupled with the potential for significant rain events, can add considerably to the excitement.Selecting optimum cool season cover crop mixes is challenging since there are so many factors involved. The optimum mix provides early and uniform stand establishment, good weed competition, and minimal pest and disease pressure. It “catches” potentially leachable nutrients, does not lodge or fall over in high wind and heavy rainfall events, does not set viable seed prior to incorporation, fixes nitrogen, does not get too carbonaceous prior to incorporation, and is relatively easy to incorporate and quick to break down once incorporated. The ideal mix also improves overall soil health and helps form stable soil aggregates by providing adequate amounts of carbon as a food source for the soil microbial communities. A good standard mix that has proven successful at the Center for Agroecology & Sustainable Food Systems Farm on the UC Santa Cruz campus over the past 20 years is a 50/50 mix of bell beans and lana vetch with no more than 7% cayuse oats, planted at a rate of about 175 lbs per acre with a no-till drill.There are many options available for mid- and late summer cover crops in the Central Coast region. Water use and “land out of production” are the two biggest challenges with summer cover crops, but in a diverse system they can provide good weed suppression and nutrient cycling, and can significantly improve soil tilth and aggregation when planted in rotation with mixed vegetables.