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USDA Research: Does No-Till Really Capture More Carbon?

Thursday, November 5, 2009

The Agriculture Research Service (ARS) of the US Department of Agriculture released a surprising bit of climate change-related research on Tuesday, work that suggests that getting big cuts in greenhouse gas emissions from simple changes in common farming practices may not be as easy as many hope.

The study was done by scientist Jane Johnson at the ARS North Central Soil Conservation Research Laboratory in Morris, Minn. She's working on a five-year USDA project called GRACEnet (for Greenhouse Gas Reduction through Agricultural Carbon Enhancement Network) in which researchers at more than 32 sites are looking for ways to shrink agriculture's climate change footprint. This is what USDA's press release said about her findings:

In a comprehensive study, she raised corn, soybean, wheat and alfalfa in rotation so that each crop grew in the same year, on plots treated with and without fertilizer. She also used a less-aggressive tillage system known as strip tillage, in which only narrow bands of soil are tilled instead of an entire field. For comparison, she replicated the cropping system adopted by many Minnesota farmers -- raising corn and soybeans in a two-year cycle on fertilized plots tilled with a chisel or moldboard plow.

She used a hydraulic soil probe to measure the organic carbon sequestered in the soil and closed-vented chambers to measure emissions of carbon dioxide, methane, and nitrous oxide. She found that when measured over the course of a year, greenhouse gas releases were largely the same under two-year and four-year rotation systems, and that applying nitrogen fertilizer had less overall impact than anticipated on nitrous oxide emissions. Nitrous oxide emissions peaked during spring thaws when the sun warmed the soil, regardless of which tillage or rotation system was used.

Chisel and moldboard plowing increased carbon dioxide emissions for a short time. But measured over the course of a year, carbon dioxide emissions were no different from plots with intensive tillage than plots without it (EWG emphasis). She also found no consistent patterns to methane releases.

EWG Midwest vice-president Craig Cox had this reaction after reading the report of Johnson's initial findings:

This study underscores the need for independent scientific oversight of any agricultural offset program that is part of a cap-and trade-system to slow climate change. Independent scientists need to have the final say about what farming practices should qualify for generating carbon credits.

Read about it all here at the ARS news site.


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