174 
Journal of Agricultural Research 
Vol. XIV, No. 4 
SUMMARY 
The preceding pages present a comparative study of the salt require¬ 
ments for young and for mature buckwheat plants grown in nutrient 
solutions having the same initial total concentration value of 1.75 atmos¬ 
pheres, but differing in the proportions of the component salts. This 
series of solutions comprised 36 different sets of salt proportions of the 
three salts, potassium phosphate (KH 2 P 0 4 ), calcium nitrate[Ca(N 0 3 ) 2 ], 
and magnesium sulphate (MgS 0 4 ). 
The results obtained from a series of cultures grown in these solutions, 
from the flowering stage to the maturity of the plants, were compared 
with those obtained from a similar series previously carried out with the 
same solutions but conducted only to the flowering stage. The main 
results of this comparative study may be summarized briefly as follows: 
(1) The highest yield of buckwheat tops and of roots obtained in a 
period of four weeks directly following germination was produced by a 
solution characterized by the following salt proportions: Potassium 
phosphate, 0.0144 m; calcium nitrate, 0.0052 m; magnesiuiq sulphate, 
0.0200 m. The buckwheat plants grown during the second four-week 
period (including the period of seed production and ripening) in the same 
series of 3-salt solutions as were the plants harvested at the end of the 
first four-week period produced their highest yield of tops and of roots 
in a solution having the salt proportions of potassium phosphate, 
0.0108 m; calcium nitrate, 0.0130 m; magnesium sulphate, 0.0100 m. 
Thus, the maximum yield was produced during the later stage of devel¬ 
opment (series B) in a medium having a lower osmotic proportion of 
potassium phosphate, a much higher proportion of calcium nitrate, and 
a much lower one of magnesium sulphate than had the medium which 
produced the highest yield during the early growth period (series A). 
(2) The buckwheat plants respond just as readily to the variations in the 
osmotic proportions of the salts in the different solutions during the later 
period of development as they do during the early stage of growth, but this 
response is markedly different for the two different stages of development. 
(3) The values of the cation atomic ratios magnesium to calcium, 
magnesium to potassium, and calcium to potassium, characterizing the 
solutions which produced the highest yields, and also those which gave 
the lowest yields, differ markedly with the two different developmental 
stages of the plants. 
(4) The amounts of transpirational water loss during each of the two 
different periods of development, indicate, in a general way, the yields. 
High transpiration corresponds to high yields of tops, and low transpi¬ 
ration to low yields. 
(5) For each of the two developmental periods of growth considered, 
low water requirement is, in general, associated with high yields of tops 
and of roots, and high water requirement with low yields. 
(6) There is no definite correlation between the yields of tops and of 
seeds, such as there is between the yields of tops and of roots. 
