Carbon Footprints | Practical Winery & Vineyard Journal

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SEPTEMBER/OCTOBER 2009

GRAPEGROWING

GHG impact from Irrigation Strategy

Frequent, low-volume irrigation may produce less N2O than infrequent, high-volume irrigation
Drip irrigation likely causes less N2O emissions than flood or furrow irrigation at the vineyard level, but if nitrogen fertilizers are applied through the drip system, then this could offset this benefit somewhat by concentrating nitrogen in soil, which may increase N2O production under the drip emitter (this is an area of uncertainty)

GHG impacts of Cover Crops

Increase soil carbon storage (especially perennial cover crops)
Increase soil nitrogen levels (legumes) and may decrease need for synthetic fertilizers
Potential reduction in leaching of nitrogen through the soil
Potential decrease in indirect losses of N2O due to decreased leaching rates
May require tractor-mowing passes which are an additional source of fossil fuel GHG emissions
May compete with vines for water, possibly resulting in more irrigation and associated GHG emissions from pumping water
Potentially decreases losses of soil organic matter to erosion, particularly on hillsides

GHG impacts of Pruning/Thinning practices

Some vine material extracted during pruning and thinning may be incorporated into soil organic matter, increasing carbon sequestration
Fossil fuel used during mechanical canopy management can contribute substantial amounts of CO2
Removal of dead vines is a loss of carbon storage unless chipped and left in the vineyard

GHG impacts of Hedgerows and Native Vegetation

Native perennial vegetation is a significant source of carbon storage
Native oak systems store large amounts of carbon in soil and trees
Decreased potential for erosion and runoff
Decreased potential for nitrogen and/or pesticide contamination of surface and ground water

For example, in wine grapes where little fertilizer generally isused, it may be difficult to further decrease emissions of N2O.Use of organic fertilizers and cover crops instead of synthetic fertilizers tosupply necessary nitrogen may limit emissions but has not been proven.

Timing nitrogen applications to ensure maximum uptake by roots may decrease N2O emissions and nitrogen leaching,but more research is needed.

Irrigation

Vineyard water use can impact GHG emissions and carbon sequestration. The energy used during irrigation to pump water results in GHG emissions. Moreover, a correlation exists between increased irrigation and GHG emissions from soil. At high moisture content, soils have minimal oxygen content and microbes produce more N2O.

Anaerobic soils are optimal environments for microbial production of N2O(and CH4,though less important for vineyards). Wet soils, especially when warm, can also increase CO2 emissions through increased microbial activity and decomposition of organic matter.

In contrast, increasing irrigation can offset some GHG emissions by stimulating vines to grow and store carbon in permanent structures. This is a form of above ground carbon sequestration that is especially effective if vines live for many years and much of the removed vine biomass is incorporated into the soil to increase organic matter.

Various irrigation systems and patterns may differently impact GHG emissions from soils. Drip irrigation is thought to produce less N2O than flood or furrow irrigation at the vineyard level but more research is needed.

Tillage

The act of tilling soil consumes substantial quantities of fossil fuel. Estimates of fuel usage during tillage operations and potential savings from alternative management strategies can be determined using a general calculator at: http://ecat.sc.egov.usda.gov/. (Use the estimated acreage of a wheat cover crop.) The Wine Industry GHG calculator (http://www.wineinstitute.org/ghgprotocol) also performs this function.

By breaking up soil aggregates, tillage increases soil emissions of CO2 and possibly N2O by mobilizing carbon and nitrogen, thus allowing microbes to access and consume previously protected organic matter. Each

Table I: Vineyard Impacts on Atmospheric GHGs
Model Components	CO2 (X)	N2O (300X)	CH4 (25X)

Carbon Sequestration	– – –	+/–	+
Tillage	+++	+/–	+/–
Nitrogen Fertilizer	+/–	+++	–

Biomass
Vine Carbon Storage	– –	?	?
Vine Decomposition	+++	++	+
Soil Amendments
Compost	– –	++	+
Manure	– –	++	+
Lime	+/–	+/–	?
Cover Cropping	+/–	+/–	+
Irrigation Water	+/–	+++	+

Fuel Use
Vehicles	+++	++	+
Pumps	+++	++	+
Electrical Grid	+++	++	+

+ = Increase; – = Decrease; ? = Unknown; +/– = Site-Specific Number of symbols indicates relative magnitude of impact.

tillage pass causes some loss of soil sequestered carbon as CO2.

Decreased tillage not only limits CO2 emissions but minimizes losses of organic matter through erosion. While building up soil organic matter may lead to some additional CO2 and N2O production, the net balance will be greater soil carbon storage in the long term. Additional research is needed to clarify these impacts in California.

Cover Crop management

The use of cover crops can increase the storage of carbon in vineyard soils and decrease CO2 emissions. Perennial cover crops are most efficient at doing this because of their large root production. In addition to increasing soil carbon, leguminous cover crops supply nitrogen to the soil, and may be used to decrease applications of synthetic fertilizers.

Cover crops also decrease the offsite movement and loss of soil organic matter by erosion and nitrogen by leaching. The relationship between cover crops and GHG production and carbon storage is an area of ongoing research.

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