Anammox Activity and Nitrogen Dynamics in Flooded Taro Soils of Hawaii

P.D.: Jonathan Deenik
Dept. Tropical Plant & Soil Sciences, University of Hawaii
Co.-P.D.: Greg Bruland
Dept. Natural Resources & Environmental Management
University of Hawaii
Co.-P.D.: Brian Popp
Dept Geology & Geophysics
University of Hawaii
Co.-P.D.: James Tiedje
Center for Microbial Ecology
Michigan State University

The discovery of anaerobic ammonium oxidation (anammox) activity in marine sediments in 2002 has reshaped the classic nitrification-denitrification view of nitrogen cycling (Thamdrup and Dalsgaard, 2002). Anammox involves the anaerobic autotrophic oxidation of ammonium coupled with nitrite reduction. This process may be responsible for up to 70% of total N2 production in marine sediments, representing a major global N sink. Recently, members of our team detected anammox by specific primers in a variety of sediments and soils, ranging from subtropical wetlands, eutrophic lakes, and deep sea sediments to northern fen and Siberian permafrost (Penton et al., 2006). Anammox has also been independently identified in a freshwater river (Zhang et al. 2007) and lake (Schubert et al., 2006). The presence of these bacteria in freshwater sediments and soils suggests that anammox may play an even larger role in the global N cycle than previously thought.

Anammox bacteria were recently detected in soil samples collected from flooded taro fields on Oahu and in river and pond sediments on Kauai. As a previously unknown mechanism of anaerobic nitrogen (N) loss in agriculture, we propose to determine the impact of anammox in a flooded agricultural system. The goal of the project is to acquire a better understanding of the fundamental mechanisms driving anaerobic N dynamics in flooded taro systems in Hawaii in order to improve N fertilizer management. The project has two objectives: 1) to determine the distribution of anammox in flooded taro soils of Hawaii and evaluate its contribution to N2 production, and 2) to determine the effects of different N fertilizer practices on anammox activity, N dynamics, and crop yield under flooded conditions. The project will test the following general hypothesis: anammox is ubiquitous in Hawaii taro soils and its activity is significantly affected by soil management practices and redox conditions. The results of this study will generally applicable to other flooded agricultural systems.

Exciting opportunity to conduct cutting edge research on anammox in tropical flooded agricultural systems in Hawaii, Position Opening ~ Graduate Research Assistant (0.50 FTE)

Characterizing Nitrogen Mineralization and Plant N Supply from Animal Manures in Hawaii’s and Agricultural Soils

In order to improve the management of animal waste materials as fertilizer materials in crop production systems we need to understand nitrogen (N) mineralization rates in relation to plant N requirements. If we can accurately predict the amount of plant available N (PAN) from manure for a particular crop we can adjust the application rates to produce good yields and minimize N losses to leaching. Accurate estimates of PAN also allow us to predict residual N from a single manure application and adjust subsequent manure application rates to account for residual N. Currently, there is insufficient field data to predict PAN form animal manures in Hawaii soils. Such information is essential to assist farmers manage animal manures as fertilizer materials in tropical cropping systems in ways that maintain good crop production and minimize negative impacts on the environment.

Nitrogen Mineralization Potential in Important Agricultural Soils of Hawai‘i

Soil organic matter management to improve soil and crop quality on intensive vegetable farms in Hawaii

The goal of the research component of this project is to develop sensitive, reliable and simple measures of soil biological and physical properties that can be used to monitor changes in soil quality due to organic matter inputs . Soil samples from some of Hawaii’s intensive vegetable farms show significant decreases in soil organic matter with negative impacts on soil and crop quality. The importance of soil organic matter in crop production and the maintenance of soil function and health is considered the single most important indicator of soil productivity. A number of vegetable farmers on Oahu, Maui, and Hawaii Island recognize that their conventional soil management practices have had negative impacts on their soils, but they are hesitant to adopt new management practices that involve organic matter additions. A recent on-farm trial with compost showed that compost additions had significant positive effects on both soil and crop quality. Given the preliminary findings, we hypothesize that improving overall soil health by using organic matter inputs will lead to improved crop yields and quality.

Understanding Charcoal's Role in Improving Soil Quality

Using charcoal as a soil amendment is currently being proposed as an effective means to not only significantly increase terrestrial C sequestration, but also increase soil fertility and food production in the acid, infertile soils of the humid tropics. Termed “Terra Preta nova”, this approach is modeled on the C-rich anthropogenic soils known as “Terra Preta do Indio” (Indian black earth) found in Amazonia and associated with habitation sites of pre-contact Amerindian populations dating as far back as 7,000 cal yr BP. These soils are remarkable because they have remained fertile and enriched in soil C compared with adjacent forest soils despite centuries of cultivation. There are many anecdotal claims indicating that adding charcoal to soils improves soil quality. The reported results are highly variable because outcomes of such trials depend on the nature of the soil and the type and amount of charcoal applied. Would the result be the same if more or less of a different type of charcoal of smaller or larger particle size were applied to a different type of soil? We are currently studying the effect of charcoal on soil properties and plant growth in the laboratory and in greenhouse experiments.

Effects of Flashed Carbonized© Macadamia Nutshell Charcoal on Plant Growth and Soil Chemical Properties

Determining the Impacts of Water Pumping and Alien Species Invasion Stream Flow for Sustainable Water Resource Management in Makaha Valley, Hawaii

In this project I am collaborating with Dr. Miura on evaluating the use of multi-spectral and hyper-spectral satellite imagery to map the vegetation in Makaha Valley. We are interested in seeing whether these satellite based sensors can be used to differentiate invasive from native plant species with the intention of developing vegetation maps characterizing the spatial distribution of invasive and native plant species within the watershed.

Remote Sensing of Invasive Species in Makaha Valley