Rapid evaluation and screening of Arachis pintoi contributions to soil nitrate and select soil quality characteristics as a living mulch system

Mitschele, Rebecca S.
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Nitrogen (N) is an essential plant nutrient, which is often limiting in soil. In order to maximize plant growth and yield, many farmers use synthetic fertilizers to address nitrogen deficiencies. Both economic and environmental factors have lead to a focus on more sustainable methods, including using legume living mulch systems. However, sampling and monitoring N concentrations can be expensive, time consuming, and often beyond the scope of on-farm management. Therefore, the validity of rapid test methodologies should be explored. The overall goals of this project were (1) to determine the value of a rapid soil nitrate testing procedure in making informed decisions with regard to nitrogen management in sustainable agricultural systems and (2) determine the effectiveness of perennial peanut as a living mulch. In accordance with these goals, the project had the following objectives: 1) evaluate the effectiveness of a rapid commercial ion selective electrode (Horbia Spectrum Technologies, Japan), for soil solution nitrate-nitrogen analysis under a perennial peanut living mulch system, 2) examine the effects of a perennial peanut living mulch system on selected soil properties, i.e. electrical conductivity, soil nitrate-N, extractable nutrients, bulk density, gravimetric soil moisture, pH, and organic matter, 3) determine the effects of propagule type, soil type, and inoculation on perennial peanut growth and its application to a living mulch system. The Cardy meter was chosen as the rapid methodology due to wide commercial availability and favorable past research documenting sap nitrate-N applications. Field and laboratory studies were conducted to evaluate this rapid nitrate test for soil solution analysis and to determine soil type influences on the accuracy of readings. The Cardy meter measurements were compared to a standard colorimetric method that is commonly used in soil laboratories. A strong correlation (r2=O.92) between the Cardy meter and the standard laboratory colorimetric method was demonstrated across different soil types. The quick method proved to be effective as a rapid nitrate tool for both field soil solution and soil leachate samples recovered from soil columns. Using the Cardy meter, the soil nitrogen dynamics under a perennial peanut living mulch were monitored during November 2006 to May 2007. Affects of perennial peanut density on soil quality in terms of select physical and chemical properties was examined by measuring extractable nutrients (p, K, Ca, Mg, Mn. Fe, Cu, Zn), organic matter, pH and soil physical properties (bulk density and gravimetric soil moisture). Treatment levels (Low, Medium, and High) were assigned to perennial peanut biomass densities and used for analysis of variances. Results of this study demonstrate significant differences among the perennial peanut treatments for bulk density, gravimetric soil moisture, soil pH, K, Ca, Mg, Mn. Fe, and Zn. Average conductivity of soil solution under perennial peanut was positively related to soil nitrate-N, although the strength of the correlation was dependent on perennial peanut biomass and individual samples were weakly correlated (r2=O.27). Increases in soil nitrate under the perennial peanut living mulch are a result of biological fixation of atmospheric nitrogen. Therefore, perennial peanut nodulation and growth response to propagule type, inoculation, and soil type was examined in a greenhouse experiment. Perennial peanut propagule types included commercial seed obtained from Bolivia (CIAT -17434) and perennial peanut cuttings from an organic orchard in Poamoho, Oahu. Results showed that soil type had a significant affect on shoot biomass, total biomass, and plant growth. However, root biomass and nodulation did not differ between soil types. Propagule type was significant in plant growth for all plant biomass measurements and for nodulation. Nodule size was not statistically different for the main treatments. The interaction between soil type and inoculation was significant at the 90% confidence level. Inoculation did not increase biomass or nodulation for either propagule type. Therefore, inoculation is not necessary in these tested tropical soils, but propagule type should be considered when selecting perennial peanut as a cover crop.
Thesis (M.S.)--University of Hawaii at Manoa, 2007.
Includes bibliographical references (leaves 102-106).
xiii, 110 leaves, bound 29 cm
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