Role of Agriculture in Creating Zero Net Carbon

 In no other area of our local economy is the correlation of carbon generation and carbon sequestering more direct than in agriculture.  In Sonoma County, vineyards and dairies account for most agricultural activity, both for land used and for revenues generated.

 While the production of both wine and milk has processes that emit GHGs, rangeland and vineyards sequester carbon.  Much of the CO2 that is released during the production process is “new” carbon, i.e., recently “fixed”, as opposed to ancient carbon in petroleum..

 Both the dairy and wine communities still view manure, pomace, lees and vineyard canes as “waste” that has to be disposed of in the most cost-effective manner.  The options for the disposal of manure, wastewater, and vineyard canes include land applications for manure and wastewater, and burning of the canes.  None of these options is sustainable. All of them use a linear process of disposal to get rid of a waste. Ideally they would instead “close the loop” by considering each of these “wastes” as a resource to recapture and utilize. This recapture and reuse can generate additional revenue.

 Diesel Use

 Diesel use in tractors, irrigation pumps and other farm equipment is a primary source of CO2, PM10 and other GHGs.  Most of the emissions are associated with supply trucks, and to some extent, tour buses.  Recent changes in air quality regulations, especially in the San Joaquin Valley, have forced both dairies and grape growers use alternative fuels such as biodiesel in order to comply.

 Biodiesel, while an attractive alternative, has some disadvantages for the farm community.  The most problematic is the current low level of availability.  For example, one large vineyard operation in Sonoma County uses 80,000 gallons per year.  No information is available for the total amount of diesel used by the agricultural community in Sonoma County.  Some equipment manufacturers discourage biodiesel use because they will not honor warranties on equipment if biodeisel is used.  A final obstacle to biodiesel is the use of above ground diesel storage tanks (AGT).  These are rented from the diesel fuel supplier.   One company has refused to allow biodeisel to be stored in their AGTs.  Since this company does not deliver biodiesel, the vineyard is forced to decide whether they will get new AGTs for biodiesel or simply modify existing diesel engines to become cleaner burning.

One way that growers can decrease their fuel use in their irrigation operations is to participate in pump efficiency programs.  The Agricultural Pumping Efficiency Program (APEP or the "Program") is an educational and incentive rebate program developed to improve overall pumping plant efficiency and encourage energy conservation.

All owners or users of an electric or natural gas utility account that is used for production agriculture or large turf irrigation who are paying the Public Goods Charge may be eligible.

For more information on this program visit http://www.pumpefficiency.org/.

Methane

Methane is 21 times more powerful as a greenhouse gas than carbon dioxide and is a major contributor to global warming. According to the U.S. Department of Energy, methane is responsible for about 15 percent of the greenhouse gas buildup in the atmosphere. 

 The wastewater storage ponds at dairies and wineries emit most of the methane.  These ponds contain the waste from dairy cows and from the wine making process.  Since the waste is centralized in the pond, it becomes feasible to capture the methane for energy generation.

 The Straus dairy in Marin County demonstrates the effectiveness of this approach. Their digester system captures naturally occurring gas from manure and converts it into electricity. With this new system, Straus is expected to generate up to 600,000 kWh per year, saving about $6,000 in monthly energy costs.

Clos du Bois winery is a model for efficiency and alternative energy use.  They have installed a methane digester to harvest the methane from wastewater before it is discharged into the wastewater ponds.  Clos du Bois rerouted their existing wastewater system to run through the digester.  They are now able to replace over 75% of their natural gas use with the methane they capture and burn.

Burning Agricultural Waste

Most vineyard waste comes from pruning the canes in the fall.  In the apple orchards remaining in Sonoma County, the pruning operations occur during the same season.  The most common practice for disposing of the prunings is burning.  Regulations require that any burning in Sonoma County needs to have a permit, be supervised and can only contain organic material. 

 In addition to contributing CO₂, PM10 and PM2.5, burning agricultural material may also involve the illegal disposal of other material. This may include end-posts treated with chromated copper arsenate (CCA). These may not be burned or chipped. Chemically treated wood must be extracted prior to waste piling and disposed of at a Class II landfill.  

In the Central Valley, rapidly degrading air quality level has lead to the development of biofuel facilities where prunings from the vineyards and orchards are burned to generate electricity. The regulatory pressure in the Valley has changed the economics of agricultural waste disposal.  These same pressures are moving into Sonoma County and the same waste streams can be collected to generate energy for our own community.

Carbon Sequestration

Carbon sequestration can be defined as the retention of carbon to prevent or delay its release to the atmosphere as CO₂.  Plants are considered a “sink” for CO₂ because they uptake this gas during photosynthesis.  Because plants assimilate carbon, enhancing their populations helps limit atmospheric concentrations of carbon dioxide.  Perennial plants are particularly efficient at carbon sequestration because carbon is stored in permanent structures.  Grapevines in California, for example, were estimated to assimilate 251,084 tons of CO₂ into permanent structures in 1992. [i]

 Carbon sequestration can be increased by maximizing and diversifying vegetation in and around the vineyard. For example, utilizing cover crops (especially permanent covers), maintaining or planting hedgerows, seeding unpaved roadways and other areas, and planting trees and shrubs.  Additionally, the rate of carbon return as atmospheric CO₂ from decomposing plant tissues decreases (i.e., is better sequestered) with decreased tillage.  The proliferation of plants and minimization of tillage also improves air quality by mitigating airborne dusts and PM10s.

 For dairies, the increase in stream setbacks and restoration of riparian habitats can be permanent contribution to carbon sequestering.  Programs are available to encourage and assist land owners to rehabilitate the riparian corridors.  Many of these programs are associated with salmon and steelhead recovery projects. 

 Another alternative for the agricultural community is to get tax incentives by placing land in conservation easements.  These easements allow for dairies, vineyards, wineries, ranchlands and other agricultural operations to set land aside for preservation.  These lands can be restored to earlier ecosystems. Shrubs and trees could be grown that would remove more carbon from the atmosphere and sequester carbon for long term storage.

Growing Fuel

The ability to grow a fuel source here in the County does not seem economically feasible at this time.  While ethanol and biodiesel are the primary alternative fuels they are made from corn and soy, neither of which can be commercially grown in Sonoma County. 

 There are some feasibility studies underway to tap into grape seeds and mustard seed as a potential feedstock for the nascent biodiesel industry in the North Bay.  While these sources will never be enough to offset the amount of petroleum-based diesel used in the County, their collection could contribute to the economic viability of small scale biodeisel production.  It may also stimulate more growers to consider mustard as a cover crop for their vineyards.   

Alternative Fuel Sources

The current agricultural “waste” in the County has the potential to be collected, centralized and converted to renewable energy .  Orchard and vineyard prunings, pomace, lees and manure are all viable sources of feedstock for renewable energy production.  While there is some composting occurring, especially with pomace and lees from the wine community, this is always done away from where methane and other GHGs are released.

The potential exists for collecting this material as part of a secondary resource network to capture the methane in a biogas process.  This process will allow for the recovery of local waste material to be used as a fuel while protecting the atmosphere from releases of methane, PM10s, PM2.5s and other GHGs.  In addition, the by-product of the biogas process is compost.  This material can be returned to the vineyard for soil amendments.

Other Resources

Climate Friendly Farming