Title: Biochars impact on soil moisture storage in an Ultisol and two Aridisols Authors
|Amonette, James -|
|Gaskin, Julia -|
|Das, K -|
|Steiner, Christoph -|
|Ahmedna, Mohamed -|
|Rehrah, Djaafar -|
Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 23, 2012
Publication Date: May 10, 2012
Citation: Novak, J.M., Busscher, W.J., Watts, D.W., Amonette, J., Ippolito, J.A., Lima, I.M., Gaskin, J., Das, K.C., Steiner, C., Ahmedna, M., Rehrah, D., Schomberg, H.H. 2012. Biochars impact on soil moisture storage in an Ultisol and two Aridisols. Soil Science. 177(5):310-320. Interpretive Summary: Crop moisture stress occurs due to short-term droughts caused by erratic or low rainfall distribution that leads to loss of crop productivity. Crop stress could be lessened if a method were available to increase moisture storage by improving soil aggregation. We hypothesized that aggregation could be formed by amending soil with biochar, a charcoal-like substance produced as a byproduct from biofuel manufacture. Biochars were used a long time ago to amend infertile soils in South America and to improve their productivity. We evaluated nine biochars produced from four crop or wood-waste products and under high and low pyrolysis temperatures for their abilities to improve soil moisture storage and aggregation in a sandy soil from the southeastern Coastal Plain and two silt loam soils from the Pacific Northwest. The nine biochars were mixed into the three soils at a rate of about 20 tons/acre. Biochar-amended soils and a control without biochars were laboratory incubated for four months. Every month, treatments were leached with water to simulate multiple soil wettings by either rainfall or irrigation. At the end of the incubation period, soils were dried and passed through a nest of sieves to determine which size aggregates had formed. For all three soils, biochars produced from switchgrass and hardwoods increased soil moisture storage while others were benign. The high temperature pyrolyzed switchgrass caused the highest increase in soil moisture capacity. Some biochars formed aggregates while others had no effect. Since selected biochar amendments improved soil water storage, future research will focus on the reason why some biochars are effective and some are not and how the results can be ramped up to field scale.
Technical Abstract: Droughts associated with low or erratic rainfall distribution can cause detrimental crop moisture stress. This problem is exacerbated in the USA’s arid western and southeastern Coastal Plain due to poor rainfall distribution, poor soil water storage, or poorly-aggregated, subsurface hard layers that limit root penetration. We hypothesized that soil physical deficiencies may be improved by biochar applications. Research indicates a single biochar will not serve as a universal supplement to all soils; consequently, biochars may need to be designed with physico-chemical properties that can ameliorate specific soil physical deficiencies. We conducted a laboratory study that examined the effect of biochar on soil moisture retention and aggregate formation. Eight biochars were made from four feedstocks at two different pyrolysis temperature classes (<400 and >500°C; <752 and >932°C) and were characterized for their physical and chemical properties. In addition, we included a biochar made using fast pyrolysis of hardwood wastes. All biochars were mixed at 2% w/w with either a Norfolk loamy sand (Fine-loamy, kaolinitic, thermic Typic Kandiudults), a Declo silt loam (Coarse-loamy, mixed, superactive, mesic xeric Haplocalcids), or a Warden silt loam (Coarse-silty, mixed, superactive, mesic xeric Haplocambids). Amended soils were laboratory incubated in pots for up to 127 days. About every 30 days, bulk density was measured and then each pot was leached with 1.2 to 1.3 pore volumes of deionized water. Gravimetric and volumetric soil moisture contents were determined after free drainage had ceased and again 2 and 6 days after leaching. The Norfolk-treated soils were later dry-sieved, and the sum by weight of their 0.5- to 1.0-mm aggregates was determined. In general, the biochar surface area and surface tension increased when produced under higher pyrolytic temperatures (>500°C). After leaching, Norfolk soils treated with switchgrass biochars had the most significant increase in soil moisture capacities. Similar increases were found in the Declo and Warden soils. Formation of 0.5- to 1.0-mm aggregates in the Norfolk loamy sand varied with biochar. Biochars enhanced the moisture storage capacity of the Ultisol and Aridisols thereby potentially reducing the on-set of crop moisture stress; however, the effect varied considerably with biochar feedstock and pyrolysis temperature.