7 i8 
Vol. XXVII, No. jo 
Journal of Agricultural Research 
survey of the literature concludes that injury to growing sorghum plants 
by frost or drought increases the prussic-acid content, but that stunted 
growth from lack of plant food in the soil diminishes it. 
In view of these divergent conclusions as to the effect of available 
nitrogen upon the hydrocyanic-acid content, and hence as to the possi¬ 
bility of using sorghum as an indicator in studies of the availability of 
nitrogen, the writer decided to try the effect of varying amounts of nitrate* 
upon plants otherwise subjected to the same conditions. 
EXPERIMENTAL DATA 
SOILS USED 
The plants analyzed were grown in the greenhouse in stoneware jars 
8.3 inches in diameter and 8.5 inches deep. Each of the three Minnesota 
soils selected for use in the experiment were treated alike except in the 
amount of fertilizers applied. The soils were all low in nitrogen, so that 
it was to. be expected that the addition of nitrogen would produce a 
marked visible effect on the plants. They were: 
Thurston loam (subsoil), from the farm of the Minnesota Agricultural 
Experiment Station (nitrogen 0.039 per cent). 
Merrimac loamy sand, from Coon Creek Sand Experimental Fields 
(nitrogen 0.068 per cent). 
Coloma sand, from Nickerson, in Carlton County (nitrogen 0.068 per 
cent). 
TREATMENT OE SOILS 
Before the Thurston loam was placed in the jars, muriate of potash 
(52 per cent K 2 0) and superphosphate (45 percent P 2 0 5 ) were mixed into 
the soil, each at the rate of 2 pounds per ton (o. 1 per cent). 
This was equivalent to an application of 1 ton per acre of each of the 
fertilizers, an amount that should remove any question of a lack of either 
potash or phosphate. Half the jars received no nitrate, while of the 
other half each jar received 0.25 gm. at each application, this being given 
in solution at recorded intervals. The plants were very pale in color and 
made very little growth where liberal amounts of only potash and phos¬ 
phoric fertilizers were added, but where sodium nitrate in addition was 
applied the color was dark green and the growth was excellent. 
The Merrimac loamy sand is low in nitrogen, but it had just previously 
been used in the greenhouse for growing alfalfa, and its available nitrogen 
had thereby been increased. As this soil had been found not to respond 
to either potash or phosphate with farm crops, neither of these was added. 
With this soil, in the early stages of growth there was no difference in 
appearance between the plants that had received nitrate and those that 
had not, growth and color being good in both, but later, when some of the 
nitrogen furnished by the alfalfa roots had been used up, a difference 
appeared. 
On the Coloma sand, to which neither potash nor phosphate was sup¬ 
plied, the growth of the sorghum was very poor even where nitrate was 
added. 
SORGHUM EROM EIRST PLANTING 
All the jars of the three soils were planted with seed from the same lot 
on December 5, 1922. The growth from this planting was slow, due to 
the short period of sunshine daily in the winter. The plants grown from 
