38 
Journal of Agricultural Research 
Vol. XXIII, No. t 
vorable action of the sulphate. Results fully as remarkable as the forego¬ 
ing have been obtained by Mr. E. H. Mathewson, of this office, in similar 
cooperative tests at Reidsville, N. C.; and the experiments elsewhere indi¬ 
cate that the data will apply to the tobacco crop more or less generally. 
Muriate of potash tends to impair the combustibility of tobacco and in 
some cases gives less desirable colors. It seems desirable, therefore, to 
use the sulphate of potash in combination with sulphate of magnesia. 
Tests have shown that low-grade potash salts carrying more or less mag¬ 
nesia, such as Kainit and double manure salts, eliminate sand drown and 
produce much better growth than high-grade sulphate. It has been 
found, in fact, that both muriate and sulphate of potash in relatively pure 
form but still containing very small percentages of magnesium salts, such 
as some of the “high-grade” imported potash salts, are less likely to cause 
sand drown than muriate and sulphate of exceptional purity. It seems 
clear that very pure forms of potash salts should not be used as fertilizer 
for tobacco, and possibly not for other crops, unless supplemented with 
magnesia salts or materials containing magnesia. In the absence of more 
exact data double manure salts, which are essentially mixtures of sul¬ 
phate of potash and sulphate of magnesia, would seem to be a desirable 
source of potash for tobacco. Wood ashes, cottonseed-hull ashes, and 
other forms of potash of vegetable origin also should be satisfactory so far 
as concerns magnesia. 
It is to be noted that in actual fertilizer practice high-grade sulphate 
of potash has not been used very extensively in this country, and even 
when employed it is nearly always in combination with other fertilizer 
materials which contain magnesia. It is believed that the favorable 
action of cottonseed meal, tobacco stems and stalks, and bam manure 
in preventing sand drown, which has been previously discussed, is due 
to the magnesia supplied by these materials. Cottonseed meal contains 
about i per cent magnesia, and this offers a possible explanation of the 
marked preference for this fertilizer material shown by tobacco growers 
of the Connecticut Valley where color of the cured leaf is of so much 
importance. It may be that vegetable material of this character through 
gradual decay in the soil furnishes a more or less continuous source of 
magnesia in suitable quantities through the growing season. Thus, it 
seems likely that one of the functions of bam manure is to furnish mag¬ 
nesia in suitable quantity and form for plant growth. The action of 
common salt in preventing sand drown, which has been referred to, 
probably is due in part to the small percentage of magnesia which it 
usually contains, but it is also likely that salt liberates magnesia when 
applied to the soil. 
LIME IN RELATION TO SAND DROWN 
While limestones vary widely in their content of magnesium, it rarely 
happens in practice that limestone or burnt lime available for agricul¬ 
tural uses is entirely free from this element. The available evidence 
all goes to show that the quantity of magnesium required to prevent the 
sand-drown type of chlorosis is small, possibly less than 20 pounds 
per acre. In general, therefore, it is to be expected that liming the soil 
even with fairly pure limestone or its products would prevent sand drown, 
keeping in mind, of course, that the magnesia thus supplied would be 
less soluble than that furnished by most of the impure potash salts. 
The data given in Table V plainly show that liming is decidedly 
beneficial in overcoming the tendency of sulphate of potash to cause 
