40 BULLETIN 1256, U. S. DEPARTMENT OF AGRICULTURE. 



naturally contain sufficient magnesium for the plant's needs, or it 

 is supplied in the ordinary system of fertilization practiced. On 

 certain sandy soils low in natural fertility and supplied with artifi- 

 cial fertilizers containing little or no magnesium, the deficiency of 

 this element becomes evident in seasons of considerable rainfall 

 when the small supply of available magnesium may be leached away. 

 Control. — The use of so-called high-grade or relatively pure 

 mineral commercial fertilizers, especially the high-grade potash salts, 

 to the exclusion of low-grade forms or organic forms (originating 

 from vegetable or animal matter) favors the appearance of sand- 

 drown under the conditions described. The addition of sulphate or 

 chlorid of magnesium to the fertilizer salts in relatively small quan- 

 tities prevents the chlorosis. Dolomitic limestone (high in magne- 

 sium) and fertilizers of vegetable origin, as cottonseed meal, tobacco 

 stalks and stems, and barnyard manure, tend to prevent the disease. 

 A relatively small amount of magnesium is apparently sufficient to 

 remedy sand-drown, even in striking cases of deficiency, less than 50 

 pounds per acre usually being sufficient. 



POTASH STARVATION. 



The lack of sufficient potash in a soil is often characteristically indi- 

 cated by tobacco plants grown in such, soils, especially if other fer- 

 tilizing elements are not lacking. Aside from a general stunted ap- 

 pearance, the leaves become crinkled or rough and turn downward at 

 the margin. Yellowing usually starts at the leaf tips, becomes most 

 marked along the margin, but proceeds inward between the veins in 

 blotches, without sharp demarcation. A bronze or copper tinge over 

 parts of the lea£ surface is also commonly associated with the yel- 

 lowing. Smaller yellow spots may develop, which finally turn brown 

 or grayish white, and the whole leaf may finally dry up. Specking 

 or spotting may also be characteristically associated with these symp- 

 toms of potash hunger. Leaves deficient in potash are frequently 

 brittle both in the green and cured condition (PI. II, fig. 2). 



If symptoms of potash starvation are noted sufficiently early, some 

 benefit may come from a liberal application of a readily available 

 potash salt between the rows of the growing crop. The fertilizer 

 formula for the following year's crop should contain both some 

 readily available and some slowly available potash. 



OTHER MALNUTRITION SYMPTOMS. 



A deficiency of other elements in the soil is not so characteristically 

 indicated as in the case of potash and magnesium. The lack of nitro- 

 gen is indicated in most plants by a light-green to yellow color and 

 stunting. This condition is brought about as well, however, by a 

 number of other variable factors, such as deficiency or excess of wa- 

 ter, poor tilth, or shortage of light, so that not much reliance can be 

 placed upon it. Excess of nitrogen tends to produce a large dark- 

 green, heavy-bodied, coarse leaf usually undesirable except in dark 

 export types of tobacco. 



In case of phosphoric-acid deficiency the plants may remain nor- 

 mally green or even (urn darker given than ordinarily, particularly 

 in the case of young plants. In case of marked deficiency of this ele- 



