April 22, 2012
Can California agriculture help increase carbon sequestration?
The carbon cycle is currently out of balance. Humans have introduced too much carbon dioxide to the atmosphere from burning fossil fuels, causing climate change and changing weather patterns. We have the technology to do work with nature to sequester more carbon. Agricultural land accounts for 455 million acres of the total land area in the US of 1.9 billion acres. Unfortunately, since the time that we have settled the land, the soil organic content has dropped to about less than one-fourth of what it once was.
Humans could sequester organic carbon into soil if we operated farms and ranches with practices that increase and maintain the organic material in the soil. For example, conventional farm practices that include improper tillage and overuse of chemical fertilizers result in about 20,000 pounds of carbon dioxide. We can help control the CO2 released by adding organic material to the soil. Practices in which soil is mulched and rarely tilled result in a dramatic decrease in the loss of carbon dioxide from the soil. Tilling the soil upsets soil life and exposes it to sunlight and oxidation, releasing large amounts of CO2. In the natural environment, the carbon-based roots and other soil life are rarely exposed or destroyed. Such oxidation naturally takes place, but the natural process is much slower, so plants can capture the CO2 and reprocess it instead of letting it into the atmosphere.
California is a huge venue for carbon storage potential, as much of California’s agriculture is perennial. Perennial crop residue is more readily decomposed than annual residues, and perennials store carbon within the woody biomass of trees and vines. Further, with the increase in agricultural yields, the biomass returned to the soils has increased, promoting sequestration. Rice farmers have also contributed to sequestration efforts. Instead of burning the fields after harvest, most of the crop residue is now returned to the soil. Through similar small efforts, California agriculture can greatly increase its agricultural carbon sequestration.
Although there has not been significant research into vineyards as carbon sequestration resources, they hold high potential. Permanent cover cropping has been shown to increase soil organic matter when used instead of bare fallow rotations. Growing cover crops, however, can be negatively impacted by one light tillage annually. Further research is needed to understand the ability of different cover crops to increase soil carbon in vineyards. Still, there have not been many studies of vineyards and carbon sequestration. Vineyard specific studies are needed to understand the effects of vineyard management practices on carbon storage.
California could almost double carbon sequestration by adapting conservation tillage practices and returning prunings to the soil. This assumes that area for perennial agriculture continues to expand, and that the biomass of crops continues to grow. As of 2002, California’s agriculture was not sequestering through conservation tillage although the practice is commonly cited as sequestering carbon by reducing soil respiration. Due to the low erosion potential of the land and the high intensity multicropping, California agriculture has not widely adopted conservation tillage. If further research were done on adapting conservation tillage to California agriculture, we could help restore balance to the carbon cycle.
Sources:
http://www.greenhq.net/carbon-cycle/
http://www.jstor.org.libproxy.usc.edu/stable/40061767
http://www.sustainablewinegrowing.org/docs/CSWA%20GHG%20Report_Final.pdf
Christopher Miranda is an undergraduate in the USC Dana and David Dornsife College of Letters, Arts and Sciences.
October 31, 2011
Where would California agriculture be without the carbon cycle?
The amount of global carbon outputs have increased with the industrial revolution and rising need for agriculture, brought about by a rapid population growth. Agriculture over the years has become a major contributor to the global carbon cycle, especially as it now accounts for approximately 14% of global land use. It tends to deplete soil carbon because land used for agriculture has a lower net primary productivity than land that is kept in it’s natural state with undisturbed soil and processes.
In order to better understand the ways in which we are emitting carbon and effecting the carbon cycle, one must better understand the cycle itself. Carbon is absorbed by plants during photosynthesis in the form of carbon dioxide, along with sunlight and water. Plants then produce glucose and oxygen. When plants decompose, the carbon is transferred to the soil, where it is stored along with mineral carbon. Additionally, when animals eat plants, the carbon is passed from one to the other. Therefore this carbon can be released into the atmosphere during the respiration of plants and animals, the burning of fossil fuels, or, in the case of farming, when soil is tilled (Soil Science and Management 5th Edition, Plaster).
California’s agriculture tends to differ from that in the rest of the US in that it grows a large amount of perennial crops and specialty crops such as vegetables, nuts and fruits. California’s climate makes it the ideal provider of specialized high value crops to the rest of America, and much of its economy has been built on this industry. Perennial orchards and vineyards account for roughly a third of agricultural land (Kroodsma and Field). Since California has long hot summers, irrigated soils go through distinctive wet and dry cycles between water applications, which impacts the amount of dissolved organic carbon in soils. For these reasons, it’s evident that the carbon cycle is particularly vital in California industries and agriculture (Kroodsma and Fields).
California has smaller levels of carbon sequestration, most likely largely due to warmer temperatures, irrigation, and a strong lack of conservation tillage. This practice disturbs the soil less, but is not practiced as much in California because there is less of a risk of erosion than in the rest of the US. However, carbon storage in California is improved by the growth of perennial agriculture. It agitates the soil less and decomposes faster than annual plants.
There are practices, both farming and industrial, that can be put into effect in California’s agriculture to reduce carbon emissions. Farmers can implement increased use of conservation tillage to leave soil undisturbed and reduce emissions. They can also return pruning of plants to the soil as mulch. It has been proven that if soil is mulched, rarely tilled and has plants growing, loss of CO2 is decreased. Waste wood from orchards and vineyards can be used in biomass power-plants, both to reduce waste and the burning of fossil fuels. California has already begun decreasing field burnings, as that releases CO2 (Kroodsma and Fields). These practices implemented together would reduce carbon emissions while simultaneously improving crop yields and productivity.
About the authors: Lily Phillips and Ariana Verdu are working towards their bachelor degrees in the USC Dornsife College of Letters, Arts and Sciences.