Through the cultivation of fruitful and  extensive collaborations across the Hawaiian Islands, the continental U.S. and the Pacific Basin, I have been involved in cutting-edge research addressing challenges communities face in maintaining environmental quality (water, soil, and air), agricultural productivity, and human health. I obtained funding and led a USDA-NRI funded research project that discovered the presence of anammox bacteria in flooded taro fields and quantified the occurrence of rhizosphere-mediated nitrogen transformations leading to fertilizer N loss in the subsoil. My biochar work began with the characterization of volatile matter and ash content and their effects on soil fertility, and has moved to the use of biochar to remediate Mn toxicity in acid soils. My lab has also been involved in developing improved techniques to measure clay content in tropical soils known for their inherent resistance to dispersion. For the Children’s Healthy Living Project, I have led the design, development, and implementation of a prevalence survey of 4-6 year old children (N=1,000) to determine obesity prevalence and characterize family diet across  7 Micronesian islands (Majuro, Ailinglaplap, Kosrae, Pohnpei, Yap, Ulithi, and Palau). I supervise 6 locally hired staff and two Junior Researchers. Currently, I am leading the implementation of an agricultural census in Pohnpei and developing methodology including use of remote sensing technologies to quantify the extent and productivity of the agroforest system. These data will be used in conjunction with dietary and socio-economic data to better understand the factors that contribute to child and family health.


Taro Research

Deenik, J.L., G.L. Bruland, B. Popp, and J. Tiedje.  Anammox Activity and Nitrogen Dynamics in Flooded Taro Soils of Hawaii. USDA-NRI Soil Processes. (2008-2013)

Predicting N losses in flooded agricultural systems is complex due to the large number of potential N transformation pathways. The project consisted of two broad objectives: 1) to determine the N balance of flooded taro agricultural fields using conventional and isotope-based measurements, and 2) to characterize N transformations in an intensively managed flooded agroecosystem.


Penton, C.R., J.L. Deenik, B.N. Popp, G.L. Bruland, P. Engstrom, J. Mueller, A. Worden, and J. Tiedje. 2014. Assessing nitrogen transformations in a flooded agroecosystem using the isotope pairing technique and nitrogen functional gene abundances. Soil Science 179:2-10.

Penton, C.R., J.L. Deenik, B.N. Popp, G.L. Bruland, P. Engstrom, D. St Louis, G.A. Brown, and J. Tiedje. 2013. Importance of sub-surface rhizosphere-mediated coupled nitrification-denitrification in a flooded agroecosystem in Hawaii. Soil Biology and Biochemistry 57:362-373.

Deenik, J.L., C. R. Penton, and G.L. Bruland. 2013. Nitrogen cycling in flooded taro agriculture. Cooperative Extension Service Publication, CTAHR, SCM-31, pp. 8.

Deenik, J.L. and G.L. Bruland. (2010-2012). Alternative Nitrogen Fertilizer Management Strategies to Improve Water Quality and Fertilizer Recovery in Wetland Taro Production Systems. Supplemental HATCH Funding.

Current N fertilization practice on most commercial taro farms consists of monthly applications of urea directly into the surface water of the ponded fields, which may pose potential downstream N contamination of fragile freshwater and marine ecosystems. A controlled experiment with four treatments including a check plot (no fertilizer), fish bone meal organic fertilizer (FBM), Duration® (polymer coated urea) fertilizer, and a farmer  practice using conventional urea fertilizer was established at four commercial farms in Hanalei Valley. Fertilizer treatment effects on water and soil N concentration was assessed through water and soil sampling. Analysis of variance was used to evaluate treatment effects on taro yield, fertilizer N use efficiency, and economic return to the farmer.

Fertilizer treatment had no significant effect on mean taro yield. The polymer coated urea (PCU) controlled release fertilizer showed the highest average yield and lowest amount of variation. The fish bone meal (FBM) and PCU fertilizers provided a long term reservoir of plant available N in the root zone, and reduced N export to the river system in effluent water. The current farmer practice did not store applied N in the soil, but rather showed an increased export of N to the river system with potential to contaminate fragile downstream freshwater and marine ecosystems. Varying fertilizer did not improve N use efficiency. Results from a partial cost benefit analysis showed that the PCU fertilizer treatment showed the highest mean return with the lowest variability across the three farm sites.

Results from the experiment indicate that the Duration® PCU product from Agrium Technologies is an economically viable alternative to conventional urea with the added benefit that it will reduce potential N contamination of fragile downstream aquatic resources. Further on-farm tests are recommended to confirm that net returns are higher or similar to conventional fertilization over time.


Since explorer Herbert Smith’s discovery of the fertile Terra Preta soils of Amazonia in the late 19th century and Wim Soembroek’s work (1966) attributing Terra Preta fertility to human inputs of charcoal as long as 7,000 years ago, there has been an ever increasing amount of research devoted to the use of charcoal (now termed biochar) as a soil amendment to increase fertility, crop productivity and simultaneously increase carbon sequestration. Through collaborations with faculty in the Hawaii Natural Energy Institute (Dr. Michael Antal, Jr and Dr. Michael Cooney), the Department of Natural Resources and Environmental Management (Dr. Susan Crow) and Dr. Patma Vityakon at Khon Kaen University my lab has been engaged in evaluating the use of different biochars for soil improvement.

Biochar and Nitrogen Dynamics


Slide Presentations

Biochar and Soil Acidity



Butnan, S., J.L. Deenik, B. Toomsan, M.J. Antal Jr., and P. Vityakon. 2014. Biochar characteristics and application rates affecting corn growth and properties of soils contrasting in texture and Mineralogy. Geoderma (In Press)

Deenik, J. L., A. Diarra, G. Uehara, S. Campbell, Y. Sumiyoshi and M. J. Antal. 2011. Charcoal Ash and Volatile Matter Effects on Soil Properties and Plant Growth in an Acid Ultisol. Soil Science 176(7): 336-345.

Deenik, J.L., T. McClellan, G. Uehara, M.J. Antal, and S. Campbell. 2010. Charcoal volatile matter content influences plant growth and soil nitrogen transformations. Soil Sci. Soc. Am. J. 74:1259-1270

Improving Clay Measurement in Tropical Soils


Silva, J.H., J.L. Deenik, R.S. Yost, G.L. Bruland, and S.E. Crow. 2014. Improving clay content measurement in oxidic and volcanic ash soils of Hawai‘i by increasing dispersant concentration and ultrasonic energy levels. Geoderma (In Press)