• Assessment And Prediction Of Potentially Mineralizable Organic Nitrogen For Subarctic Alaska Soils

      Zhao, Aiqin; Zhang, Mingchu (2011)
      The objective of this study was to identify a rapid laboratory technique to predict potentially mineralizable organic N for subarctic Alaska soils. Soil samples were taken from major agricultural area of subarctic Alaska. Laboratory incubation followed by kinetic model fit was first used to select a best model to estimate potential soil N mineralization. By correlating the model estimated organic N pool sizes and different chemical extracted organic N, I then found the best chemical method to estimate soil potentially mineralizable N. Spectroscopic properties of water extractable organic matter were also determined and correlated with model estimated organic N pool sizes in order to improve the estimation of soil mineralizable N pool. Finally, the best chemical method and spectroscopic property were used in the selected best kinetic model for the prediction of soil N mineralization in field incubation. Model comparisons showed that models with fixed rate constants were better than that the ones with rate constants estimated from simulation. Among models with fixed rate constants, fixed double exponential model was best. This model differentiated active mineralizable organic N pool with a fixed rate constant of 0.693 week-1 and slow mineralizable organic N pool with a fixed rate constant of 0.051 week-1. By correlating model estimated organic N pool size and chemical extracted organic N amount, I found that the potentially mineralizable organic N size was closely correlated with hot (80 �C) water extractable organic N or 1 M NaOH hydrolysable organic N. By correlating model estimated organic N size and spectroscopic characteristics of water extractable organic matter, I found that the active mineralizable organic N pool was correlated with humification index in cold (22 �C) water extraction (R 2=0.89, p<0.05), which indicates that characterizing extracted organic matter was a useful tool to improve the estimation of soil organic N pools. In summary, potential mineralizable organic N in soils from subarctic Alaska can be estimated by hot water extractable organic matter or 1 M NaOH hydrolysable organic N, which accounted for 70% and 63% of the variation in potentially mineralizable organic N, respectively. This approach will provide fundamental insight for farmers to manage N fertilizer application in agricultural land and also provide some basic information for ecologists on predicting N release from Alaska soil that can be used for assessing the N impact on ecosystem.
    • Effects Of Migratory Geese On Nitrogen Availability And Primary Productivity In Subarctic Barley Fields

      Pugin, Jennifer Adrienne; Sparrow, Stephen (1996)
      Agricultural areas are important for migratory geese, providing easy access to high energy foods. Geese affect agricultural production by removing biomass and by depositing fecal nutrients. This study used $\sp{15}$N as a tracer to examine the quantitative effects of fecal nitrogen contributions on agricultural production.<p> During winter 1994-95, 12-week lab incubations were conducted to determine net nitrogen and carbon mineralization potentials in soils amended with barley straw, grain, and goose feces. The greatest rates of nitrogen mineralization occurred in the soil amended with goose feces. Carbon mineralization occurred at the greatest rate in the soil amended with grain.<p> In comparison to barley grain and straw, goose feces provided the greatest amount of available nitrogen to the soil and to subsequent crops, and consequently higher barley yields (59 and 62% increase, respectively). However, supplementary fertilizer is still necessary for farmers to obtain maximum barley yields. <p>
    • Phenanthrene Adsorption And Desorption By Melanoidins And Marine Sediment Humic Acids

      Terschak, John Andrew; Henrichs, Susan M. (2002)
      Sediments are major reservoirs of persistent petroleum contamination in marine environments. Petroleum hydrocarbons associate with the sediment organic matter, of which humic acids are an important constituent. This study examined the role that humic acid and its structure plays in the kinetics and mechanisms of polycyclic aromatic hydrocarbon (PAH) interactions with sediments. Natural humic acids, with a wide range of properties, were isolated from Alaska coastal marine sediments. Melanoidins were synthesized and used as humic acid analogs. The humic acids were characterized by elemental and isotopic analyses, Fourier transform infrared spectroscopy, and cross-polarized magic angle spinning 13C nuclear magnetic resonance spectroscopy. The humic acids were coated onto a standard montmorillonite clay, and the adsorption and desorption of phenanthrene was measured using a radiotracer. Adsorption required about one week to reach steady state, indicative of slow diffusion of PAH within the humic acid. The composition of the humic acids had a greater effect on phenanthrene adsorption than their concentrations on the clay. Organic carbon normalized adsorption partition coefficients were closely correlated with the sum of amide and carboxylic carbons, a measure of the polarity of the humic acids, but were independent of initial phenanthrene concentration, indicating that the binding sites were unlimited and uniform in strength. This explains the fact that initial adsorbed concentration of phenanthrene had no effect on subsequent phenanthrene adsorption. Desorption of phenanthrene was not related to any of the humic acid structural characteristics measured. The initial desorption rate was linearly related to the initial adsorbed concentration, as expected for a diffusive process, and was negatively correlated with the carbon content of the humic acid coated clay. Under most conditions, desorption was complete after one to seven days; there was little evidence for irreversible adsorption. Because of the substantial variability of adsorption and desorption behavior with organic matter characteristics, interactions of aromatic hydrocarbons with marine sediments cannot be predicted based on total organic matter concentration alone. Information on aspects of organic matter composition is needed in order to make accurate predictions.
    • Soil Fertility And Corn And Soybean Yield And Quality In A Six-Year Nitrogen And Phosphorus Fertilization Experiment

      Anthony, Peter M.; Sparrow, Stephen; Malzer, Gary; David, Valentine,; Zhang, Mingcho (2012)
      Optimum management of nitrogen (N) and phosphorus (P) fertilizers for corn [Zea mays L.] and soybean [Glycine max (L.) Merr.] production requires quantitative understanding of multiple soil processes and crop responses, including supply and immobilization of N and P by soil, the response of yield and quality to nutrient availability, and the relationships and interactions between N and P cycling, crop response, and other soil physical and chemical variables. We conducted a six-year experiment on two 16-ha fields on glacial-till soils in south-central Minnesota. In each year of a corn--soybean rotation, we measured soil physical and chemical parameters and grain yield and quality at a 0.014-ha resolution within each field. These observations coincided with placement of a randomized complete block, split plot design of N and P fertilizer treatments. Spatial patterns of mineralizable N were consistent over time. Mineralizable N was highly correlated to soil nitrate at a well-drained site, but not at a poorly-drained site. Increases in available soil P per kg of net P addition were significantly related to soil pH. Within fields, spatial patterns of soybean yields were highly correlated across years, and we observed consistent relationships between yield and soil variables. Overall, soybean yield related positively to soil P and Zn and negatively to pH at all site-years. Quadratic-plateau regression models of soybean yield in relation to soil P and Zn indicate that in high pH soils at these sites, yield is optimized when soil P and Zn levels are higher than current recommendations. Corn yields responded significantly to N rate and N rate by P rate interaction in all site-years. Whole-field economic optimum N rate differed significantly by site-year and by P treatment at some site-years. Site-specific P fertilization should account for spatial variation in soil P buffering capacity. Nitrogen mineralization and NxP nutrient interactions should be accounted for in agronomic management decisions for corn production. The consistent influence of soil pH on nutrient cycling and crop response indicates the potential benefit to amelioration of high pH in calcareous glacial-till soils. Results highlight the significance of spatial variability in nutrient cycling to crop management.