15n Techniques and Analytical Procedures

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Excerpt from 15n Techniques and Analytical Procedures: Indo/U. S. Science and Technology InitiativeThe quantitative evaluation of pool sizes, metabolite pathways, chemical reactions, equilibrium products, or N-fractions at some sampling time in each system studied is based upon classical isotope dilution (gest et al. 1947 and Inghram For example, when 15nh4 fertilizer is mixed with soil, the 15nh4 will equilibrate with the indigenous soil nh4. This mixture will then take part in chemical and biological processes, and eventually the 1sn will be found in plant and soil biomass, organic matter, and inorganic N compounds. Once 15n is detected in any tissues or compound we know qualitatively that the transformation has oc curred, but quantitative estimates of the magnitude of the transformation are determined by dilution equa tions. Probably the main advantage of 15n dilution is its usefulness to determine qualitative differences in treatments, i.e., types of cultivars, types of fertilizers, the timing and placement of fertilizer applications, and various forms of management, including irrigation, tillage, residue, herbicides, and pesticides. Using isn dilution calculations to make N balances for an entire cropping system or cropping sequence has many problems. These problems arise from errors associated with sampling (temporal and spatial variability), with measuring the soil bulk densities and soil weights for various soil profile depths, with measuring crop yields, and with determining the total N and the 15n abun dance of each component of the system.When planning a study, the researcher should make some rough estimates of the amount of unlabeled N in the various N pools that will be measured and thereby estimate the amount of dilution that will occur to his isn amendment. The isn enrichment of the added compound should be of sufficient magnitude that the 15n can be easily detected after dilution. Many investi gators (gest et al. 1947, Jansson 1958, Huser 1966, Hauck and Bremner 1976, Fiedler 1984) have provided mathematical expressions that can be used to make dilution calculations. Hauck and Bremner (1976) discussed in detail numerous dilution equations, including the following.About the PublisherForgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.comThis book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully, any imperfections that remain are intentionally left to preserve the state of such historical works.