State Water Resources Research Institute Program


Project Id: 2010AZ389B
Title: Biochar soil amendments to increase the water holding capacity of sandy, arid soils
Project Type: Research
Start Date: 4/01/2010
End Date: 3/31/2011
Congressional District: 8
Focus Categories: Agriculture, Conservation, Water Use
Keywords: biochar, charcoal, water, water holding capacity
Principal Investigator: Artiola, Janick
Federal Funds: $ 10,000
Non-Federal Matching Funds: $ 21,449
Abstract: According the Arizona Department of Water Resources, the State's annual water budget is about 7 million acre-feet see Figure 2. About 40% of this water is imported from the Colorado River. Groundwater accounts for nearly 44% of the water budget and the remainder is provided by in-state rivers (14%) and reclaimed water (2.4%). Arizona is entering into the second decade of statewide drought. In response to present and future concerns about water resources, the Governor of Arizona in 2007 signed a Drought Declaration for the State, asking everyone to "increase water conservation efforts" (ADWR website).

Agriculture in Arizona accounts for about 70% of the total State's water use. In addition, flood and furrow irrigation, known to have poor (<50%) irrigation efficiencies, are the primary methods of water delivery to Arizona crops. Sandy soils, such as those present in Red Rock and the Yuma valley do not retain water efficiently and require more irrigations than loamy Arizona soils, to maintain adequate water supplies to crops during the growth season.

Agricultural soils in AZ usually contain less than 1% total organic carbon (TOC), but are usually rich in carbonate minerals. A study by Artiola and Pepper (1992) measured the TOC of an agricultural field that had received ten consecutive yearly applications of eight dry mT of biosolids. They found no significant change in the TOC content in the top 1.5 m of the soil. This is because the carbon mineralization rates are very high (>70% annually), precluding significant organic carbon accumulations in soils even from repeated biosolids applications.

Biochar, also known as charcoal or black carbon, is produced by pyrolysis (oxygen-limited combustion) of biofuels such as agricultural residues. Research has demonstrated that the highly porous nature of biochar materials allows then to act as sponges and modify the soil texture, thereby increasing soil water holding capacities. These effects (that need to be quantified and studied further) are likely to be maximized in light-textured sandy soils. The beneficial effects of biochar-amended soils may extend many years due to the refractory (chemically and biologically stable) nature of this carbon form with estimated half-lives in the soil environment ranging from 100-1000s of years. Therefore, these and other benefits (CO2 emissions reductions, carbon storage, and energy production) may make these materials ideal soil amendments. This project will focus on determining how the addition of biochars, derived from various Arizona biofuel residues (examples: sweet sorghum bagasse, pine wood residues) affects some physical properties of sandy semi-arid soils. The ability of soils to retain water is linked to their texture and organic matter content, we will look at changes in soil water holding capacities; with varying biochar loading rates and different biochar materials and biochar particle sizes, using laboratory and small field plot studies. In addition, to soil moisture, soil physical changes will be linked to soil energy balance by measuring surface albedo and soil profile temperatures over time.

This research will focus specifically on measuring the effects of biochar additions in Arizona related to water holding capacity. This can be accomplished using small field plots instrumented to collect soil moisture, temperature and albedo data over a six to 12-month period. During this period, additional biochar soil characterization data will be generated in the laboratory to supplement and support the findings of the field research.

Progress/Completion Report, 2010, PDF

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