Determination of nitrogen in soil and plant materials: Use of boric acid in the micro‐kjeldahl method

Abstract

The use of boric acid for trapping ammonia in the micro-Kjeldahl determination is examined. A suitable procedure, together with a modified type of micro-distillation apparatus. is described.The buffer capacity of boric acid solutions was examined in relation to the sensitivity in the titration of ammonia dissolved in them. Two grades of boric acid, ' pure ' (technical) and AnalaR, were compared ; the former showed appreciable buffering on the acid side.The p H values of solutions of both grades de.creased with increasing concentration. The sensitivity of the three indicators examined for the titration of ammonia diminished with increasing concentration of boric acid as a result of the increased buffering. With concentrated boric acid, all three indicators showed wide transitional periods at the endpoint, but in solutions of concentration up to 1.0% of AnalaR grade the end-points shown by all three indicators were sharp. The methylene blue-methyl red indicator, however, was generally preferable.The ammonia-fixing capacity of boric acid was studied-in air-bubbling tests and by recoveryof a known amount of ammonia by distillation. A volume of 10 ml. of I.O?& boric acid fixed 5 mg. of nitrogen as ammonia sufficiently firmly to afford accurate analyses. For macro-determinations, IOO ml. of 2.0% boric acid held firmly up to go mg. of nitrogen.

Optimum Leaf Removal Increases Nitrogen Accumulation in Kernels of Maize Grown at High Density

“…Nitrogen concentration (g kg −1 ) in each sample was determined using the semi-micro Kjedahl method3738. Meanwhile, N accumulation (g plant −1 ) was calculated as the product of dry matter (g) and N concentration (g kg −1 ) in each plant organ.…”

The critical relationship between soil moisture content in the region of wilting point and the mineralization of natural soil nitrogen

“…Ammonia nitrogen was extracted from a 30 g. sample with potassium chloride by Richardson's (1938) modification of Olsen's method. The ammonia nitrogen was distilled off from an aliquot in a Markham apparatus after Yuen & Pollard (1953), except that the mixed indicator preferred in this laboratory is methyl red-bromo-cresol green. Nitrate nitrogen was extracted from a 25 g. sample with the dilute calcium sulphate reagent of Roller & McKaig (1939), and determined colorimetrically using a solution of 5 % brucine in chloroform and a ratio of soil extract to concentrated sulphuric acid The period of incubation was 32 days, and samples •were •withdrawn at regular intervals during this time in each of the experiments.…”

Managing the seeding rate to improve nitrogen-use efficiency of winter wheat

“…The NO 3 -N concentrations were determined by colourimetric cadmium reduction (Wagner, 1974) and those of NH 4 -N were determined with a spectrophotometric method by which a coloured complex of NH 4 -N and sodium salicylate was formed in the presence of prussic acid and chloride (Benesch and Mangelsdorf, 1972). The dried soil samples were analysed for organic matter content (Walkley and Black method;Walkley and Black, 1934), total N (semi-micro Kjeldahl method; Kjeltec TM 8200 Auto Distillation Unit, Foss, Hillerød, Denmark; Bremner, 1960;Yuen and Pollard, 1953), available phosphorus (Olsen method; Zandstra, 1968) and available potassium (Dirks-Sheffer method; Melich, 1953).…”

“…Then, the ears were divided into grains and glumes and ear rachis (weighed by the difference between dry ear dry matter and grain dry matter). The oven-dried samples were milled and analysed for N concentration (semi-micro Kjeldahl method; Kjeltec 8200 Auto Distillation Unit; Foss, Hillerød, Denmark; Bremner, 1960;Yuen and Pollard, 1953), and N accumulation was calculated by multiplying the element concentration by dry weight.…”