652 STATE BOARD OF AGRICULTURE. 



TABLE 18.— PLANTS GROWN IN WASHED AND UNWASHED GREENHOUSE SOIL. 



Inasmuch as the evaporation rate is rather high uiidev greenhouse 

 conditions, there is a tendency for the soluble constituents to accumulate 

 at the surface unless the soils are watered frequently. If the solulde 

 salt content is high this is certain to occur. It may be cited for example 

 that the surface Vi-inch layer of soil in the flat revealed a very high 

 concentration 24 hours after moistening, the freezing point depression 

 being 1.35°, the soil being saturated with water when the determination 

 was made. 



niSCUSSIOX OF RESULTS. 



Salt translocation in soils is due mainly to water movements. The 

 data obtained from experiments in which water movements were pre- 

 vented show that salts added to a soil move away from the point of high 

 concentration and the rate is largely dependent upon the mass of salt 

 present as well as the water content of the soil. Now in the field the 

 total soluble salt content is relatively low and hence diffusion accounts 

 for but local movements. Tlie results of our studies of the freezing 

 point lowerings of the surface layer of soils occupied by small grains 

 and grasses and adjacent bare soils is further lu-oof, yet it is probable 

 that it operates to some degree in close proximity to the root hairs and 

 aids in furnishing the plant with substances in solution. 



When water movement takes place some of the soluble salt present is 

 carried along with it. The results of the experiments where the soils 

 were treated with substances in solution sufficiently near the surface to 

 be within the zone of upward film movement, bear this out. Moreover 

 the freezing point lowerings of samples of muck soil taken at different 

 depths from the surface as well as the accumulation of nitrates and 

 other salts at the surface of uncropped soils in larger quantities than 

 in cropped soils show that such is the case. Of course under the 

 latter conditions the lack of accumulation is doubtless due in part to 

 the removal of the nitrates and other substances by the plants. More- 

 over, the condition is probably less ideal for the formation of such on 

 account of differences in temperature of the soil and also lower water 

 contents. At any rate the salts that appeared on the surface came from 

 relatively short distances below the surface. 



Do salts move upward from subsoils to supply the plant? It is 

 considered by some that the movement of salts from the subsoil plays 

 an! important role in soil fertility. Considering the results of Leather 

 (3) in India as well as those of Burr (4). Alway (5) and others, which 



(3) Leather, .T. W. 1008. Tile Loss of Water from Soil during Dry Weather. In Dep't. of 

 Agr. India. V. 1. No. 6, 116 p., 7 fig. 



(4) Burr, W. W. 1914. The Storage and Use of Soil Moisture. Nebr. Agr. Expt. Sta. Re- 

 search Bui. 5, 88 p. 



(5) Alway, F. J. and McDale, G. R. 1917. Relation of the Water Retaining Capacity of a 

 Sou to Its Hygroscopic Coefficient. In Journ. Agr. Research V. 9, No. 2, pp. 27-71. 



