18 EXPERIMENT STATION RECOED. [Tol. 38 



ment in nitrogen and ptiosphorus. The gain of assimilable nitrc^en is ascribed 

 to bacterial fixation of atmospheric nitrogen and to the decomposition of or- 

 ganic matter, that of the phosphorus to the action of soil organisms in liberating 

 acids which attacked the phosphates, and in converting unavailaole organic 

 phosphorus into an assimilable state. 



"The bacteria in the sterilized samples (e) were derived from the air, and 

 the enhanced fertility was chiefly due to the increase in available phosphoric 

 acid, which amounted to from 47 to 76.5 per cent in the lower layer and 88 

 to 121 per cent in the arable strata, and which is ascribed to the decomposi- 

 tion of nucleins containing 5.7 per cent of phosphorus which liberate free phos- 

 phoric acid when heated to 150° C. The nitrogen contents of the sterilized and 

 unsterilized soils were the same, and as the good effects of steril'zation could 

 not be entirely due to the increase in soluble phosphoric acid they must also be 

 accounted for by assuming that assimilable nitrogen is liberated from organic 

 matter during sterilization. The increase of available nitrogen in series (e) 

 was clearly indicated by the rich green color of the leaves of the young plants." 



Formation of " black alkali " (sodium carbonate) in calcareous soils, 

 J. F. Bkeazeale (U. S. Dept. Agr., Jour. Agr. Research, 10 (1917), No. 11, pp. 

 541-590, pi. 1, figs. 26). — Studies on the formation of sodium carbonate in cal- 

 careous soils are reported from which the following conclusions were drawn : 



" In the reaction between sodium nitrate (or sodium chlorid or sodium sul- 

 phate) and calcium carbonate, resulting in the formation of sodium carbonate, 

 the presence of relatively small amounts of calcium nitrate or calcium chlorid 

 in the reaction impedes and may prevent the formation of sodium carbonate. 

 The presence of a saturated solution of calcium sulphate in this reaction does 

 not entirely stop the formation of sodium carbonate. 



" Sodium nitrate, sodium chlorid, and sodium sulphate in the presence of 

 carbon dioxid react with calcium carbonate with the formation of sodium 

 bicarbonate. The presence of relatively small amounts of calcium nitrate or 

 calcium chlorid in this reaction impedes and finally prevents the formation of 

 sodium bicarbonate. The presence of calcium sulphate has no effect in pre- 

 venting the formation of sodium bicarbonate when sodium sulphate or a mix- 

 ture containing sodium sulphate reacts with calcium carbonate. A field appli- 

 cation of gypsum will probably have no effect in overcoming black alkali if 

 the soil already contains soluble sulphates in appreciable amounts, or the 

 irrigation water contains these salts. 



" Sodium nitrate, sodium chlorid, and sodium sulphate increase the solubility 

 of calcium carbonate in the soil. Sodium nitrate, sodium chlorid, and sodium 

 sulphate react with calcium carbonate in the soil with the formation of sodium 

 carbonate (black alkali). Sodium carbonate, formed by the above reaction 

 decomposes the organic matter of the soil. Calcium carbonate has a slightly 

 destructive action upon the organic matter of the soil. Sodium carbonate is 

 much more destructive upon organic matter than sodium bicarbonate. 



" The alkali crusts that accumulate upon the soil in some irrigated regions 

 are due in part to the action of sodium salts upon calcium carbonate with the 

 formation of sodium carbonate. Barren, or ' slick,' spots are often due to 

 the action of sodium nitrate, sodium chlorid, or sodium sulphate upon calcium 

 carbonate with the formation of sodium carbonate. Sodium chlorid and sodium 

 sulphate have a protective action upon organic matter in the presence of 

 sodium carbonate. A calcareous hardpan often produces black alkali." 



The soil survey of Iowa, W. H. Stevenson, P. E. Bbown, and F. B. Howe 

 (Iowa Sta. Soil Survey Rpt. 1, Ahs. {1911), pp. S-16, fig. 1). — This is an ab- 

 stract of Soil Survey Report 1 of the station (E. S. R., 37, p. 211). 



