Influence of Biochar on Nitrogen Fractions in a Coastal Plain Soil

Authors: Schomberg, Harry; GASKIN, JULIA - University Of Georgia; HARRIS, K - University Of Georgia; DAS, K - University Of Georgia; Novak, Jeffrey; Busscher, Warren; Watts, Donald - Don; Woodroof, Robin; Lima, Isabel; AHMEDNA, MOHAMED - North Carolina Agricultural And Technical State University; REHRAH, DJAAFAR - North Carolina Agricultural And Technical State University; XING, BAOSHAN - University Of Massachusetts

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/8/2011
Publication Date: 7/12/2012
Citation: Schomberg, H.H., Gaskin, J.W., Harris, K., Das, K.C., Novak, J.M., Busscher, W.J., Watts, D.W., Woodroof, R.H., Lima, I.M., Ahmedna, M., Rehrah, D., Xing, B. 2012. Influence of Biochar on Nitrogen Fractions in a Coastal Plain Soil. Journal of Environmental Quality. 41(4):1087-1095.

Interpretive Summary: Biochar is the residual material created from the pyrolysis or heating of plant biomass to produce synthetic gasses for biofuels. Biochar has a high carbon (C) content and could be used for long-term storage of C in soils as a tool for reducing green house gas emissions. In addition, application of biochar to soils may improve soil properties like aggregation and water holding capacity that influence crop production. Limited information is available on how biochar might influence different N pools in the soil and N availability to crops. Scientists from the Agricultural Research Service locations at Watkinsville, GA, Florence, SC, New Orleans, LA, along with scientists from the University of Georgia, North Carolina Agricultural & Technological State University, and the University of Massachusetts evaluated several biochars for their effects on N pools in a Norfolk loamy sand. The biochars included ones made from peanut hull, pecan shell, poultry litter, and switchgrass at high and low temperatures and a commercially available hardwood biochar (CQuest™) We added nitrogen to the soil biochar mixtures for half of the treatments as ammonium nitrate. At the start of the experiment we observed a large loss of N from soils with the pecan shell, peanut hull, and poultry litter biochars. This was due to an increase of pH caused by the biochars. The losses were due to ammonium volatilization which we confirmed in a short term experiment. In the longer term experiment, after 127 d, little evidence of increased inorganic N retention was found for any of the biochar treatments. There was no increase in the mineralizable N fraction, indicating the microbial population did not increase with biochar additions. Some losses in the resistant N fraction were found but were primarily in the biochars that had high pH and high ash contents. The range of responses to the different biochars illustrates the need to carefully manage land application of biochar. Chemical and physical characterization of the biochar is needed to aid in matching it to the best soil type as well as appropriate land use.

Technical Abstract: Interest in use of biochar from pyrolysis of biomass to sequester C and improve soil productivity has increased; however, research has shown biochar has a high variability in physical and chemical characteristics. Greater understanding is needed about the effects of biochar on soil N dynamics in agricultural systems. We evaluated effects of peanut (Arachis hypogaea L.) hull, pecan (Carya illinoinensis Wangenh. K. Koch) shell, poultry litter, and switchgrass (Panicum virgatum L.) biochars made at high (=500 oC) and low (=400 oC) temperatures (HT and LT) and hardwood (CQuest™) biochar on N dynamics in a Norfolk loamy sand with and without NH4NO3. Changes in inorganic, mineralizable, resistant, and fixed N fractions were determined following 127-d incubation with four leaching events. A large loss of N was observed initially with the HT pecan shell, HT peanut hull, and HT and LT poultry litter biochars which had high pH and ash contents. Volatilization of N as NH3 in the presence of these biochars was confirmed in a short term experiment. After 127 d, little evidence of increased inorganic N retention was found for any of the biochar treatments. There was no increase in the mineralizable N fraction, indicating microbial biomass was not stimulated with biochar addition. Decreases in the resistant N fraction were associated with the high pH/ high ash biochars. The range of responses to the different biochars illustrate the need to manage land application of biochar by characterizing the biochar and matching it to soil type as well as land use.