Marion LeRoy Jackson

Bio: Marion LeRoy Jackson is an academic researcher. The author has contributed to research in topics: Null (mathematics). The author has an hindex of 1, co-authored 1 publications receiving 13425 citations.

Soil Chemical Analysis

Abstract: Soil chemical analysis , Soil chemical analysis , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Iron Oxide Removal from Soils and Clays by a Dithionite-Citrate System Buffered with Sodium Bicarbonate

Abstract: The oxidation potential of dithionite (Na2S2O4) increases from 0.37 V to 0.73 V with increase in pH from 6 to 9, because hydroxyl is consumed during oxidation of dithionite. At the same time the amount of iron oxide dissolved in 15 minutes falls off (from 100 percent to less than 1 percent extracted) with increase in pH from 6 to 12 owing to solubility product relationships of iron oxides. An optimum pH for maximum reaction kinetics occurs at approximately pH 7.3. A buffer is needed to hold the pH at the optimum level because 4 moles of OH are used up in reaction with each mole of Na2S2O4 oxidized. Tests show that NaHCO3 effectively serves as a buffer in this application. Crystalline hematite dissolved in amounts of several hundred milligrams in 2 min. Crystalline goethite dissolved more slowly, but dissolved during the two or three 15 min treatments normally given for iron oxide removal from soils and clays. A series of methods for the extraction of iron oxides from soils and clays was tested with soils high in free iron oxides and with nontronite and other iron-bearing clays. It was found that the bicarbonate-buffered Na2S2O4-citrate system was the most effective in removal of free iron oxides from latosolic soils, and the least destructive of iron silicate clays as indicated by least loss in cation exchange capacity after the iron oxide removal treatment. With soils the decrease was very little but with the very susceptible Woody district nontronite, the decrease was about 17 percent as contrasted to 35–80 percent with other methods.

Determination of nitrogen in soil by the Kjeldahl method

Abstract: 1 The reliability of the Kjeldahl method for the determination of nitrogen in soils has been investigated using a range of soils containing from 0·03 to 2·7% nitrogen2 The same result was obtained when soil was analysed by a variety of Kjeldahl procedures which included methods known to recover various forms of nitrogen not determined by Kjeldahl procedures commonly employed for soil analysis From this and other evidence presented it is concluded that very little, if any, of the nitrogen in the soils examined was in the form of highly refractory nitrogen compounds or of compounds containing N—N or N—O linkages3 Results by the method of determining nitrogen in soils recommended by the Association of Official Agricultural Chemists were 10–37% lower than those obtained by other methods tested Satisfactory results were obtained by this method when the period of digestion recommended was increased4 Ammonium-N fixed by clay minerals is determined by the Kjeldahl method5 Selenium and mercury are considerably more effective than copper for catalysis of Kjeldahl digestion of soil Conditions leading to loss of nitrogen using selenium are defined, and difficulties encountered using mercury are discussed6 The most important factor in Kjeldahl analysis is the temperature of digestion with sulphuric acid, which is controlled largely by the amount of potassium (or sodium) sulphate used for digestion7 The period of digestion required for Kjeldahl analysis of soil depends on the concentration of potassium sulphate in the digest When the concentration is low (eg 0·3 g/ml sulphuric acid) it is necessary to digest for several hours; when it is high (eg 1·0 g/ml sulphuric acid) short periods of digestion are adequate Catalysts greatly affect the rate of digestion when the salt concentration is low, but have little effect when the salt concentration is high8 Nitrogen is lost during Kjeldahl analysis when the temperature of digestion exceeds about 400° C9 Determinations of the amounts of sulphuric acid consumed by various mineral and organic soils during Kjeldahl digestion showed that there is little risk of loss of nitrogen under the conditions usually employed for Kjeldahl digestion of soil Acid consumption values for various soil constituents are given, from which the amounts of sulphuric acid likely to be consumed during Kjeldahl digestion of different types of soil can be calculated10 Semi-micro Kjeldahl methods of determining soil nitrogen gave the same results as macro-Kjeldahl methods11 The use of the Hoskins apparatus for the determination of ammonium is described12 It is concluded that the Kjeldahl method is satisfactory for the determination of nitrogen in soils provided a few simple precautions are observed The merits and defects of different Kjeldahl procedures are discussed