Frequently Asked Questions about climate change and agriculture: Part 3

August 14, 2012
By Chad Kruger

To get you up to speed, here are the first two questions:

1.The EPA says agriculture only accounts for 6% of US greenhouse gas emissions. Shouldn’t we focus our efforts on bigger problems such as coal fired power plants and automobile emissions instead?

2. Do “food miles” – the distance that food travels from producer to consumer – really matter to the climate?

Today’s FAQ is

Is organic farming “climate-friendly”?

While there are many general principles and concepts that are broadly considered part of the culture of organic agriculture, modern “organic farming” is actually now legislatively defined as a specific set of agriculture and food production standards regulated by a diversity of national and international bodies. The USDA National Organic Program defines Certified Organic as:

“…a labeling term that indicates that the food or other agricultural product has been produced through approved methods that integrate cultural, biological, and mechanical practices that foster cycling of resources, promote ecological balance, and conserve biodiversity. Synthetic fertilizers, sewage sludge, irradiation, and genetic engineering may not be used.” (Source: USDA NOP Website)

The fact that there is a substantial diversity of management principles, practices and production systems utilized by organic farmers to achieve a balanced set of environmental outcomes makes it impossible to provide a scientifically definitive answer to the question of whether organic farming is “climate friendly”. Therefore, the best approach to addressing this question is to evaluate a set of organic management principles and indicate whether they have generally “positive” or “negative” impacts on global carbon, greenhouse gas, and energy balances.

Carbon

Carbon sequestration is the ability of the soil to capture carbon and prevent its release to the atmosphere as carbon dioxide. The more carbon the soil can sequester, the greater the benefit. Three factors affect the ability of soils to sequester carbon: initial organic matter level, input of organic matter, and disturbance of the soil. Initial organic matter level is extremely dependent on location and prior soil management and has a definitive impact on whether any production system will increase or decrease soil carbon levels. The lower the level of initial organic matter, the easier it is to increase carbon sequestration – even without utilizing the most progressive management practices.

  • Because organic farms cannot used synthetic nutrients they are generally dependent on the use of organic amendments (i.e. manure, composts) or cover crops (i.e. nitrogen-fixing plants grown and “sacrificed” to the soil) to provide the necessary fertility to grow food plants. A side benefit of using organic nutrient management strategies is that these generally increase the overall organic matter input to the soil. An area of general uncertainty and concern, though, is that many organic amendments are sources of methane (CH4) – a potent greenhouse gas – when they are stored or processed. Generally positive, with some uncertainty due to potential methane emissions.
  • Because organic farms cannot use synthetic herbicides they are generally dependent on mechanical cultivation (i.e. tillage) as a weed management strategy. Tillage works for controlling weeds because it creates soil disturbance. Organic farmers use a range of tillage implements and strategies that vary greatly in both intensity and frequency of tillage. Negative and a problem that really needs to be solved for organic farmers.

Nitrogen

The supply of nitrogen is essential for producing any crop whether it is organic or not. The problems with nitrogen are it is both energetically expensive to produce and it creates significant, direct greenhouse gas emissions when it is used.

  • As discussed above, organic farmers cannot use synthetic forms of nitrogen and are therefore dependent on either organic amendments or nitrogen-fixing plants. These sources of nutrients, therefore, are not credited with the substantial energy-related emissions caused by the production of anhydrous ammonia for synthetic fertilizers. However, depending on the source and type of organic amendment, there may be significant energy used and emissions generated in transportation and application of organic amendments, very little of which has been quantified in the scientific literature. Positive if the source of organic nutrients is close in proximity to the field where they are used, negative if there is a lot of distance or energy required to produce and apply the amendment.
  • All sources of nitrogen used (synthetic, organic amendments, nitrogen fixed by plants) lead to emissions of nitrous oxide (N20) – a very potent greenhouse gas. The specific environmental conditions that lead to emissions of N2O are the combination of excess nitrate (the plant-available form of nitrogen), excess moisture and warm temperatures – and while N2O emissions are generally reported as an average percentage of the amount of nitrogen applied, the combination of the above conditions can lead to significant additional emissions of N2O above the predicted average. Many organic farms tend to be nitrogen constrained – meaning that nitrogen is often the limiting factor of production – and nitrate that becomes available from organic amendments is usually readily taken up by the crop. However, it’s also important to realize that it is much more challenging to manage the total supply of nitrogen from organic amendments and therefore the susceptibility to negative N2O emission events could be higher if not managed well. Positive or negative depending on the quality of management and weather events.

Energy

Energy use may actually be the most challenging factor to consider in understanding the carbon footprint of organic farming. In principle, organic production is intended to better utilize cycling solar energy to produce food (i.e. cover crops, soil-building practices, etc.), but in practice the dependence on tillage and the use of processed and transported organic amendments can have a significant negative impact on energy use. The incredible density of energy content of fossil fuels makes it very challenging in practice to overcome our dependence on fossil energy sources for traction power in farming.

  • Tillage was discussed above as a generally negative management practice for soil carbon, but it also has generally negative implications for energy use. The heavier the tillage implement needed and the more frequent tillage is used, the more energy required for tillage. One of the most significant positive results from the implementation of “no-till” farming is the significant reduction in fossil fuel energy required for producing crops (ranging from 50-85% energy reductions). Most no-till farms use a chemical herbicide strategy for weed control not available to organic farmers, which indicates that the goal of reducing synthetic chemical use and soil disturbance might not be compatible. Negative.
  • As discussed above, the supply of nitrogen and other nutrients can be an energy-intensive strategy regardless of whether a farm is organic or not. The old adage that “manure should only be transported to fields that you can see from the barnyard” is a good indicator of the energetics of processing and transporting organic amendments. Positive if the nutrient sources are produced/managed on-farm, negative if nutrients are transported from distant locations.

More detailed discussion and presentation of these issues is available in a webinar developed by three colleagues working on evaluating the climate impacts of organic farming, Lynne Carpenter-Boggs, Dave Huggins and David Granatstein:

http://www.extension.org/pages/30835/greenhouse-gases-and-agriculture:-where-does-organic-farming-fit-webinar

In addition to the OFOOT (Organic Farming Footprints) Project described in the webinar above, WSU scientists are working on a number of other cutting edge research projects to improve our understanding of and the “climate-friendly” performance of organic farming systems. These include:

  • A study evaluating the climate impacts of transitioning a farm to organic production
  • Several studies focused on reducing/eliminating tillage-based soil disturbance in organic farming systems, including organic vegetable production systems, tree fruit understory management, and dryland wheat production systems
  • Several studies focused on the recovery and densification of nutrients from organic wastes as energy-efficient organic soil amendments following methane recovery

Up next: Part 4 – Are cows really worse for the climate than cars?

One comment on “Frequently Asked Questions about climate change and agriculture: Part 3”

  1. Paleo Diet said on November 30, 2012:

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